Wednesday, August 17, 2022

Attitudes toward public female toplessness appear to be driven more by individual opinions than by context (e.g., beach, park) or structural factors (e.g., region or state-legality)

Objectification and Reactions toward Public Female Toplessness in the United States: Looking Beyond Legal Approval. Colin R. Harbke & Dana F. Lindemann. Sexuality & Culture, Aug 17 2022.

Abstract: Multiple United States federal courts have recently drawn inferences regarding community sentiment as it pertains to public female toplessness. Despite citing common social factors in their rulings, the courts have rendered conflicting decisions to uphold (Ocean City, MD) or to overturn (Fort Collins, CO) female-specific bans. Regional differences in attitudes toward toplessness may in part explain these discrepant legal outcomes. Participants (n = 326) were asked to rate their general impressions of photos depicting topless women in three different public settings. Geographic region was unrelated to reactions toward toplessness, however, participants from states with prohibitive or ambiguous statutes rated the photos differently. Consistent with a body of theoretical and empirical work on cultural objectification of women, female participants, on average, were more critical of the photos of other topless women. Other demographic and attitudinal predictors showed a pattern that suggests moral objections as a likely source of unfavorable reactions. Ascribing morality with the practice of toplessness echoed some of the commentary that surrounded the above legal cases and further substantiates prior objectification research (i.e., Madonna-whore dichotomy). Overall, attitudes toward public female toplessness appear to be driven more by individual opinions than by context (e.g., beach, park) or structural factors (e.g., region or state-legality).

Bored and better: Finding a boring person results in people feeling not only superior to the boring individual, but also to others

Bored and better: Interpersonal boredom results in people feeling not only superior to the boring individual, but also to others. Jonathan Gallegos,Karen GasperORCID Icon &Nathaniel E. C. Schermerhorn. Self and Identity, Aug 16 2022.

Abstract: Four experiments tested the hypothesis that meeting someone new who is boring would result in people feeling superior to the boring individual, which would then result in people viewing themselves as better than others and increased confidence. Respondents reported greater feelings of superiority, meaninglessness, and difficulty paying attention when they wrote about meeting a new, boring individual than a new or manipulative individual. Feeling superior, but not meaninglessness and attention, mediated the effect of interpersonal boredom on viewing oneself as better than others, but not on confidence. These finding did not occur when people wrote about a boring task or a disliked, manipulative individual. The experiments elucidate how interpersonal boredom, albeit a negative experience, can enhance people’s sense of self.

Keywords: Interpersonal boredomsuperiorityself-enhancementmeaninglessness

Less than 50pct of Psychology research were successfully replicated by preregistered studies

Röseler, Lukas, Taisia Gendlina, Josefine Krapp, Noemi Labusch, and Astrid Schütz. 2022. “Successes and Failures of Replications: A Meta-analysis of Independent Replication Studies Based on the OSF Registries.” MetaArXiv. August 16. doi:10.31222/

Abstract: A considerable proportion of psychological research has not been replicable, and estimates range from 9% to 77% for nonreplicable results. The extent to which vast proportions of studies in the field are replicable is still unknown, as researchers lack incentives for publishing individual replication studies. When preregistering replication studies via the Open Science Foundation website (OSF,, researchers can publicly register their results without having to publish them and thus circumvent file-drawer effects. We analyzed data from 139 replication studies for which the results were publicly registered on the OSF and found that out of 62 reports that included the authors’ assessments, 23 were categorized as “informative failures to replicate” by the original authors. 24 studies allowed for comparisons between the original and replication effect sizes, and whereas 75% of the original effects were statistically significant, only 30% of the replication effects were. The replication effects were also significantly smaller than the original effects (approx. 38% the size). Replication closeness did not moderate the difference between the original and the replication effects. Our results provide a glimpse into estimating replicability for studies from a wide range of psychological fields chosen for replication by independent groups of researchers. We invite researchers to browse the Replication Database (ReD) ShinyApp, which we created to check for whether seminal studies from their respective fields have been replicated. Our data and code are available online:

Tuesday, August 16, 2022

From 2018... Against commonly held views, cynical individuals generally do worse on cognitive ability and academic competency tasks

 From 2018... The Cynical Genius Illusion: Exploring and Debunking Lay Beliefs About Cynicism and Competence. Olga Stavrova, Daniel Ehlebracht. Personality and Social Psychology Bulletin, July 11, 2018.

Abstract: Cynicism refers to a negative appraisal of human nature—a belief that self-interest is the ultimate motive guiding human behavior. We explored laypersons’ beliefs about cynicism and competence and to what extent these beliefs correspond to reality. Four studies showed that laypeople tend to believe in cynical individuals’ cognitive superiority. A further three studies based on the data of about 200,000 individuals from 30 countries debunked these lay beliefs as illusionary by revealing that cynical (vs. less cynical) individuals generally do worse on cognitive ability and academic competency tasks. Cross-cultural analyses showed that competent individuals held contingent attitudes and endorsed cynicism only if it was warranted in a given sociocultural environment. Less competent individuals embraced cynicism unconditionally, suggesting that—at low levels of competence—holding a cynical worldview might represent an adaptive default strategy to avoid the potential costs of falling prey to others’ cunning.

Keywords: cynicism, competence, lay theories, social perception

The academic literature has consistently painted a dim picture of cynicism, linking it to bad health outcomes, lower well-being, poor relationship quality, and decreased financial success (Chen et al., 2016; Haukkala, Konttinen, Laatikainen, Kawachi, & Uutela, 2010; Stavrova & Ehlebracht, 2016). In contrast, in popular culture, cynicism seems to have a better reputation. For example, in film and fiction, the most cynical characters (e.g., Sherlock Holmes or Dr. House), although lonely and unhappy, are frequently painted as the most intelligent, witty, experienced, and knowledgeable ones. In the present studies, we explored lay beliefs about the association between cynicism and competence and tested whether these beliefs reflect empirical associations between these traits. Our results revealed that laypeople tend to endorse the “cynical genius” belief—that is, believed that cynical individuals would do better on a variety of cognitive tasks and cognitive ability tests than their less cynical counterparts. An examination of empirical associations between cynicism and competence based on the data of about 200,000 individuals from 30 countries debunked the “cynical genius” belief as illusionary. Cynical individuals are likely to do worse (rather than better) on cognitive tasks, cognitive abilities, and competencies tests, and tend to be less educated than less cynical individuals.

What is the source of the discrepancy between lay beliefs and reality? Literature on the negativity bias (Baumeister, Bratslavsky, Finkenauer, & Vohs, 2001) and loss aversion (Kahneman & Tversky, 1979) might give a clue. Findings from these research fields suggest that pain associated with negative outcomes (e.g., betrayed trust) is stronger than pleasure associated with positive outcomes (e.g., rewarded trust). Consequently, individuals might be more aware of the negative consequences of other people’s gullibility than of the positive consequences that a trusting stance and positive view of human nature often convey.

In addition, according to insights from trust research (Fetchenhauer & Dunning, 2010), when people endorse a cynical stance concerning others and consequently forgo trust, they usually do not even get a chance to learn whether their untrustworthiness assumption was correct and being cynical thus spared them a “loss”—or whether it was incorrect and therefore denied them a “win.” In other words, cynicism often precludes the possibility of experiencing negative outcomes. As a result, it might be perceived as a smarter, more successful strategy and cynical individuals might be attributed higher levels of competence than their less cynical counterparts. After all, they are highly unlikely to be betrayed, deceived, and exploited, whereas it usually remains unknown whether their cynicism resulted in missed opportunities.

Finally, the abundance of smart and witty cynics in fiction might fuel the “cynical genius illusion” as well. As the primary goal of fiction is entertainment, fictional worlds are typically more dangerous, their villains are meaner, and the costs of mistakes are higher than in reality—or, as Barack Obama (2014) put it referring to the House of Cards series: “Life in Washington is a little more boring than displayed on the screen.” In these hostile and dangerous worlds created for our entertainment, cynicism is warranted and often turns out to be essential for survival, suggesting that those who endorse it are likely to be the smart ones. Our cross-cultural analyses indirectly support this idea, showing that the negative association between competence and cynicism gets weaker with increasing levels of environmental hostility, such that in the most corrupt countries in our sample, competent individuals are not necessarily less cynical than their less competent counterparts (see Table 4).

This observation inevitably leads to the conclusion that whether the “cynical genius” belief represents an illusion or not must depend on the sociocultural environment. While we explored the empirical association between cynicism and competence across 30 countries, our conclusions regarding the perceived association are restricted to three Western countries: United States, United Kingdom, and Germany. We acknowledge that it is highly important to explore lay beliefs in other cultural contexts as well. It is possible that cross-cultural differences in the perceived association between cynicism and competence are also explained in part by the degree to which cynicism is warranted in a particular sociocultural context, with a stronger “cynical genius” belief in more versus less corrupt countries. In this case, perceived and actual associations between cynicism and competence might covary at the country level suggesting that there might be some truth to the “cynical genius illusion” after all.

Although our reliance on large-scale publicly available datasets (Studies 4-6) facilitated a precise assessment of the empirical associations between cynicism and competence, it did not allow for a direct comparison between the actual empirical associations and lay beliefs about these associations within a given sample. As we took great care to ensure the conceptual equivalence between the measures of the former (e.g., perceived ability to solve math problems) and the latter (e.g., actual performance on numeracy tests), we are confident in the validity of our conclusions. It is also important to note that even though the “cynical genius belief” emerged consistently across the studies, its effect size showed substantial variation across the measures of cognitive competence, with the strongest effect obtained for items reflecting mathematical competence and the weakest effect obtained for items associated with verbal skills. It seems that people like to think that those who are good at scrutinizing numbers must also be good at scrutinizing other people’s intentions. Finally, besides a belief in cynics’ “cognitive competence,” our participants showed an even stronger belief in cynics’ “social incompetence.” This belief as well as the question of whether it corresponds to reality might be worth a separate, more thorough (e.g., using more diverse social tasks) investigation.

While we have shown cynicism to be positively associated with competence in lay beliefs, it is less clear what causal theory people use to explain this association. Do they think that cynicism makes people more competent or that higher levels of competence turn people into cynics? A similar question arises with respect to the causality of the empirical associations between competence and cynicism. However, higher levels of cognitive ability, academic competence, and education might protect from adverse life experiences, not only as they allow discovering potential fraud but also as they increase the chances of living in a safe and friendly environment, providing more evidence for a positive than for a negative view of human nature and consequently preventing cynicism development. Our findings showing that cognitive ability in adolescence contributes to decreased levels of cynicism in adulthood provide some preliminary support for a causal effect of competence. However, another causal direction is possible as well: As cynicism is closely related to distrust (Singelis, Hubbard, Her, & An, 2003), cynical (vs. less cynical) individuals might be more distrustful of the opinions and knowledge of others, a behavior that can eventually prevent them from expanding their knowledge and understanding. We hope that future studies will pick up here and explore the causal directions underlying both perceived (i.e., lay beliefs) and empirical association between competence and cynicism.

To conclude, the idea of cynical individuals being more competent, intelligent, and experienced than less cynical ones appears to be quite common and widespread, yet, as demonstrated by our estimates of the true empirical associations between cynicism and competence, largely illusory. As Stephan Colbert, an American comedian, writer, and television host, phrased it, “Cynicism masquerades as wisdom, but it is the furthest thing from it.”

Monday, August 15, 2022

Instead of the human larynx having increased complexity, it has actually simplified relative to other primates, allowing for clearer sound production with less aural chaos

Evolutionary loss of complexity in human vocal anatomy as an adaptation for speech. Takeshi Nishimura et al. Science, Aug 11 2022, Vol 377, Issue 6607, pp. 760-763. DOI: 10.1126/science.abm1574

When less is more in the evolution of language

Complexity from simplification

Human speech and language are highly complex, consisting of a large number of sounds. The human phonal apparatus, the larynx, has acquired the capability to create a wider array of sounds, even though previous work has revealed many similarities between our larynx and those in other primates. Looking across a large number of primates, Nishimura et al. used a combination of anatomical, phonal, and modeling approaches to characterize sound production in the larynx (see the Perspective by Gouzoules). They found that instead of the human larynx having increased complexity, it has actually simplified relative to other primates, allowing for clearer sound production with less aural chaos. —SNV

Abstract: Human speech production obeys the same acoustic principles as vocal production in other animals but has distinctive features: A stable vocal source is filtered by rapidly changing formant frequencies. To understand speech evolution, we examined a wide range of primates, combining observations of phonation with mathematical modeling. We found that source stability relies upon simplifications in laryngeal anatomy, specifically the loss of air sacs and vocal membranes. We conclude that the evolutionary loss of vocal membranes allows human speech to mostly avoid the spontaneous nonlinear phenomena and acoustic chaos common in other primate vocalizations. This loss allows our larynx to produce stable, harmonic-rich phonation, ideally highlighting formant changes that convey most phonetic information. Paradoxically, the increased complexity of human spoken language thus followed simplification of our laryngeal anatomy.

Why are males not doing these environmental behaviors?: exploring males’ psychological barriers to environmental action

Why are males not doing these environmental behaviors?: exploring males’ psychological barriers to environmental action. Jessica E. Desrochers & John M. Zelenski. Current Psychology, Aug 13 2022.

Abstract: Previous research has reported that females are more likely than males to do pro-environmental behaviors. This research focused on understanding this relationship by exploring individual difference characteristics that may explain the sex difference, specifically traits and psychological barriers to pro-environmental action. Two studies (N = 246 and N = 357) confirm that males were less likely to report doing pro-environmental behaviors; males also reported more of Gifford’s (2011) Dragons of Inaction Psychological Barriers (DIP-Barriers) to pro-environmental action than females. Broad traits predicted pro-environmental attitudes and behaviors similar to past research, but they did not account for the sex difference. In addition, we suggest a new psychological barrier for males: perceptions of femininity may dissuade males from some pro-environmental behaviors. Results provide preliminary support for this idea and complement previous suggestions that environmentalism is perceived as more feminine. We discuss ways that future research can build on these suggestions with the ultimate goal of more effectively promoting environmentalism to males.

Sunday, August 14, 2022

Do Funding Agencies Select and Enable Risky Research? In the European Research Council, applicants with a history of risky research are less likely to be selected for funding than those without such a history

Do Funding Agencies Select and Enable Risky Research: Evidence from ERC Using Novelty as a Proxy of Risk Taking. Reinhilde Veugelers, Jian Wang & Paula Stephan. NBER Working Paper, 30320. Aug 2022. DOI 10.3386/w30320

Abstract: Concern exists that public funding of science is increasingly risk averse. Funders have addressed this concern by soliciting the submission of high-risk research to either regular or specially designed programs. Little evidence, however, has been gathered to examine the extent to which such programs and initiatives accomplish their stated goal. This paper sets out to study this using data from the European Research Council (ERC), a program within the EC, established in 2007 to support high-risk/high-gain research. We examine whether the ERC selected researchers with a track record of conducting risky research. We proxy high-risk by a measure of novelty in the publication records of applicants both before and after the application, recognizing that it is but one dimension of risk. We control and interact the risk measure with high-gain by tracking whether the applicant has one or more top 1% highly cited papers in their field. We find that applicants with a history of risky research are less likely to be selected for funding than those without such a history, especially early career applicants. This selection penalty for high-risk also holds among those applicants with a history of high-gain publications. To test whether receiving a long and generous prestigious ERC grant promotes risk taking, we employ a diff-in-diff approach. We find no evidence of a significant positive risk treatment effect for advanced grantees. Only for early career grantees do we find that recipients are more likely to engage in risky research, but only compared to applicants who are unsuccessful at the second stage. This positive treatment effect is in part due to unsuccessful applicants cutting back on risky research. We cautiously interpret this as a “lesson learned” that risk is not rewarded.

Naive Stoic Ideology, a misinterpretation of stoic philosophy: There is a negative association between stoic ideology and well-being

Misunderstood Stoicism: The negative Association Between Stoic Ideology and well-Being. Johannes Alfons Karl, Paul Verhaeghen, Shelley N. Aikman, Stian Solem, Espen R. Lassen & Ronald Fischer. Journal of Happiness Studies, Aug 12 2022.

Abstract: Ancient philosophy proposed a wide range of possible approaches to life which may enhance well-being. Stoic philosophy has influenced various therapeutic traditions. Individuals today may adopt an approach to life representing a naive Stoic Ideology, which nevertheless reflects a misinterpretation of stoic philosophy. How do these interpretations affect well-being and meaning in life? We examine the differential effects of Stoic Ideology on eudaimonic versus hedonic well-being across three cultural contexts. In this pre-registered study, across samples in New Zealand (N = 636), Norway (N = 290), and the US (N = 381) we found that a) Stoic Ideology can be measured across all three contexts and b) Converging evidence that Stoic Ideology was negatively related to both hedonic well-being and eudaimonic well-being. Focusing on specific relationships, we found especially pronounced effects for Taciturnity (the desire to not express emotions) and Serenity (the desire to feel less emotions). Despite being a misinterpretation of stoic philosophy, these findings highlight the important role of individuals’ orientations to emotional processing for well-being.


Across three cultures we investigated how a naïve stoic ideology, which captures a laypersons’ misunderstood Stoicism (as expressed in stoic ideology), might be associated with approaches to, and actual levels of, well-being. We initially predicted that stoic ideology would show a more negative association with hedonic compared to eudaimonic aspects of well-being. This was overall not confirmed. While we found that stoic ideology was more negatively associated with hedonic well-being in New Zealand, this was the only relationship in the predicted direction. Our findings, using the stoic ideology scale, are consistent with previous studies using similar measures of hedonic well-being (Bei et al., 2013; Murray et al., 2008). Importantly, on a facet level this effect was mostly driven by Taciturnity and Serenity for Eudaimonia and Hedonia. The exception was hedonic orientation to happiness which was only associated with Serenity. This pattern implies that the tendency and desire to suppress one’s problems, both experience and expression, is related to lower well-being, both hedonic and eudaimonic. Across the three countries the pattern of relationships was largely identical for higher order stoic ideology with the potential exception of the association between stoic ideology and hedonic orientation in Norway. The traditional stereotype of Nordic cultures also features a rather stoic outlook on life, which emphasizes emotional control, doing ‘your own thing’ without complaining or expressing strong emotional reactions (Saville-Troike & Tannen, 1985; Stivers et al., 2009; Tsai & Chentsova-Dutton, 2003), stoic ideology might therefore be less related to orientations to well-being. Due to the cross-sectional nature of our study, we cannot untangle whether stoic ideology only influences responding, or, as some studies have indicated, has conceptually causal relationships to well-being, theoretically driven by reduced help-seeking for example (Kaukiainen & Kõlves, 2020; Rughani et al., 2011).

It is important to highlight that our hypotheses were based on a measure which captures stoic ideology as a naïve belief system, which does not represent the philosophical ethical system underpinning Stoicism. Current psychological measures of naive stoic ideology do not capture the richness of the wider stoic belief system within classic philosophical discussions. We encourage researchers to make it explicitly clear when they are referring to Stoicism (the philosophical belief system) or stoic ideology (as captured in the Pathak-Wieten Stoic ideology scale) as an expression of a lay stoic ideological system. Future research should clarify the relationship between Stoicism and stoicism, to explore overlaps and divergences. Investigations into this area appear important, especially given the positive well-being effects of the aforementioned therapeutic approaches that are conceptually based in Stoicism (Beck, 1979; Ellis, 1962; Robertson, 2019), and the presumed malleability of stoic ideology (Pathak et al., 2017).

In future research, it would be essential to compare the relationship of the Pathak-Wieten scale empirically with measures incorporating a wider range of stoic attitudes and behaviors (centering around issues of controllability of the environment, and teleology of the universe). This is not to indicate that the Pathak-Wieten scale is not a useful tool to measure stoic ideology (but possibly not Stoicism). As we have shown here, the scale shows good measurement properties across the cultures included in our study, and reliably shows good fit across samples. From a psychometric perspective, it is a reliable and equivalent scale that can be used to compare correlation patterns across samples. The major question to be addressed in further research is what the instrument measures conceptually. As the lack of scalar invariance implies, the items measure potentially additional concepts across the different cultural contexts, which together with the philosophical questions, clearly requires further analyses and development.

At the same time, the measure provides important insight into potential determinants of reduced well-being. Given the consistent negative relationships that we found between stoic ideology and well-being across cultures, clinical practitioners might consider how these naive beliefs could be built upon for beneficial health outcomes. Given the findings of negative relationships between both aspects of well-being and the Taciturnity and Serenity facets in particular, individuals might be encouraged to share personal problems in appropriate ways and to acknowledge emotions, rather than suppressing or ignoring emotional experiences. Our study also supports previous notions (Benita et al., 2020; Gross, 2013) that it might be beneficial for individuals’ well-being to engage in practices that foster an accepting or non-judgmental stance to their emotions, for example mindfulness practices (Dundas et al., 2017), rather than suppressing their emotions. Obviously, we are unable to point towards causal directions, but the therapeutic literature using stoic philosophy principles as well as related philosophical concepts, such as mindfulness, clearly suggests that such behavioral changes may have positive health consequences.


Our current study was mostly limited by our samples, based on student populations. This limits the generalizability of our findings to the general population. However, it should be noted that the original instruments were largely developed in student samples, hence, our findings are compatible with previous research contexts. Further, we have no information on participants’ exposure to stoic philosophy, which might alter the observed association between stoic ideology and well-being. Finally, the current study, in line with previous research, focused on well-being, but not specifically on affective components. Given the conceptual overlap between stoic ideology and affective experience, future research should examine the potential link between stoic ideology beliefs, well-being, and the potential mediation role of affective experience.

Saturday, August 13, 2022

Female teams lower their contribution to the public good in the event of low likeability among members, while male teams achieve high levels of co-operation irrespective of the level of mutual likeability

I (Don’t) Like You! But Who Cares? Gender Differences in Same-Sex and Mixed-Sex Teams. Leonie Gerhards, Michael Kosfeld. The Economic Journal, Volume 130, Issue 627, April 2020, Pages 716–739,

Abstract: We study the effect of likeability on women’s and men’s team behaviour in a lab experiment. Extending a two-player public goods game and a minimum effort game by an additional pre-play stage that informs team members about their mutual likeability, we find that female teams lower their contribution to the public good in the event of low likeability, while male teams achieve high levels of co-operation irrespective of the level of mutual likeability. In mixed-sex teams, both women’s and men’s contributions depend on mutual likeability. Similar results are found in the minimum effort game. Our results offer a new perspective on gender differences in labour market outcomes: mutual dislikeability impedes team behaviour, except in all-male teams.

About half of the cobalt ends up being lost during production; indium sees losses hit 70 pct; and many metals have production losses of 95 pct or higher: arsenic, gallium, germanium, hafnium, scandium, selenium, & tellurium

Losses and lifetimes of metals in the economy. Alexandre Charpentier Poncelet, Christoph Helbig, Philippe Loubet, Antoine Beylot, Stéphanie Muller, Jacques Villeneuve, Bertrand Laratte, Andrea Thorenz, Axel Tuma & Guido Sonnemann. Nature Sustainability, corr. May 31 2022.

Abstract: The consumption of most metals continues to rise following ever-increasing population growth, affluence and technological development. Sustainability considerations urge greater resource efficiency and retention of metals in the economy. We model the fate of a yearly cohort of 61 extracted metals over time and identify where losses are expected to occur through a life-cycle lens. We find that ferrous metals have the longest lifetimes, with 150 years on average, followed by precious, non-ferrous and specialty metals with 61, 50 and 12 years on average, respectively. Production losses are the largest for 15 of the studied metals whereas use losses are the largest for barium, mercury and strontium. Losses to waste management and recycling are the largest for 43 metals, suggesting the need to improve design for better sorting and recycling and to ensure longer-lasting products, in combination with improving waste-management practices. Compared with the United Nations Environmental Programme’s recycling statistics, our results show the importance of taking a life-cycle perspective to estimate losses of metals to develop effective circular economy strategies. We provide the dataset and model used in a machine-readable format to allow further research on metal cycles.


Popular version: New study estimates how long mined metals circulate before being lost

Losses at different stages of a metal's life cycle also varied widely. We're very good at extracting most metals from ores so that most of the losses are incidental—that is, some of the metal happens to be present in an ore we use for other materials. For example, iron ore may contain something like manganese at low concentrations, but the amount of ore we process means that a lot of manganese will end up being thrown away. Overall, these losses tended to be in the area of 15 percent, with the exception of specialty metals, which averaged about 25 percent.

Both those averages obscure some fairly horrifying losses. About half of the cobalt, which is highly desired for many types of batteries, ends up being lost during production. Indium, used in many semiconductor products, sees losses hit 70 percent. And many metals have production losses of 95 percent or higher: arsenic, gallium, germanium, hafnium, scandium, selenium, and tellurium.

Losses in manufacturing are much less scary; they're generally a rounding error compared to the losses in extraction. Manufacturing produces the smallest losses for over half the metals analyzed, and there's none for which it's the highest. Even the worst rate of loss (among non-ferrous metals) only reaches 6 percent. It's clear that manufacturing has been very good at avoiding waste.

Once in use, most metals suffer minimal losses, with averages of about 5 percent or less for everything but specialty metals. But those specialty metals see losses that average over 30 percent during use. Some of them, notably strontium and barium, primarily end up in single-use products that are permanently lost to the environment (they're part of the mud injected into wells during gas and oil drilling). Those two, along with mercury, are the only three for which use is the largest source of loss.

Meta-analysis: Afternoon naps sharpen the mind; effects are small to medium

Systematic review and meta-analyses on the effects of afternoon napping on cognition. Ruth L.F. Leong, June C. Lo, Michael W.L. Chee. Sleep Medicine Reviews, August 13 2022, 101666.

Abstract: Naps are increasingly considered a means to boost cognitive performance. We quantified the cognitive effects of napping in 60 samples from 54 studies. 52 samples evaluated memory. We first evaluated effect sizes for all tests together, before separately assessing their effects on memory, vigilance, speed of processing and executive function. We next examined whether nap effects were moderated by study features of age, nap length, nap start time, habituality and prior sleep restriction. Naps showed significant benefits for the total aggregate of cognitive tests (Cohen's d = 0.379, CI95 = 0.296–0.462). Significant domain specific effects were present for declarative (Cohen's d = 0.376, CI95 = 0.269–0.482) and procedural memory (Cohen's d = 0.494, CI95 = 0.301–0.686), vigilance (Cohen's d = 0.610, CI95 = 0.291–0.929) and speed of processing (Cohen's d = 0.211, CI95 = 0.052–0.369). There were no significant moderation effects of any of the study features. Nap effects were of comparable magnitude across subgroups of each of the 5 moderators (Q values = 0.009 to 8.572, p values > 0.116). Afternoon naps have a small to medium benefit over multiple cognitive tests. These effects transcend age, nap duration and tentatively, habituality and prior nocturnal sleep.

Keywords: NapCognitionVigilanceMemoryAge effects

Friday, August 12, 2022

Check Rolf Degen's Twitter page to get great summaries of Psychology papers

 Check Rolf Degen's takes! @DegenRolf

Sweet diversity: Colonial goods (tea, coffee, sugar, tobacco) and the welfare gains from global trade after 1492

Sweet diversity: Colonial goods and the welfare gains from global trade after 1492. Jonathan Hersh, Hans-Joachim Voth. Explorations in Economic History, July 23 2022, 101468.

Abstract: When did overseas trade start to matter for living standards? Traditional real-wage indices suggest that living standards in Europe stagnated before 1800. In this paper, we argue that welfare may have actually risen substantially, but surreptitiously, because of an influx of new goods. Colonial “luxuries” such as tea, coffee, and sugar became highly coveted. Together with more simple household staples such as potatoes and tomatoes, overseas goods transformed European diets after the discovery of America and the rounding of the Cape of Good Hope. They became household items in many countries by the end of the 18th century. We apply two standard methods to calculate broad orders of magnitude of the resulting welfare gains. While they cannot be assessed precisely, gains from greater variety may well have been big enough to boost European real incomes by 10% or more (depending on the assumptions used).

Keywords: Gains from varietyGlobal tradeWelfare gains from new goodsAge of discoveryLiving standards over the long run

JEL D12D60F10F15N33

5. Conclusions

When did globalization begin to matter for living standards? According to the prevailing consensus, the answer is – not before the 19th century. O'Rourke and Williamson (2002) analysed traditional wage indices to show that trade across the Atlantic did not change real incomes before the 1830s. This paper argues that global trade quickly began to matter for living standards. As Europeans rounded the Cape of Good Hope, they brought back tea; from the New World, they brought tobacco, chocolate, and potatoes. In the Caribbean and other tropical colonies, Europeans set up a production system for sugar, tea, and coffee that transformed the supply of these goods. By the eighteenth century at the latest, consumption habits had undergone a profound transformation. New consumption goods offered variety where monotony had once reigned: hot, sweet caffeinated beverages replaced water and ale, and by revealed preference, consumers favoured tea, sugar, and coffee. Sugar also helped to reduce the culinary monotony of winter: it facilitated the making of jam and marmalade, preserving fruit flavours throughout the winter.

The welfare gains from access to new goods can be assessed by asking a counterfactual question – how much would incomes have to go up to compensate for a particular consumer item no longer being available? We use two different methods, pioneered by Hausman and Greenwood and Kopecky, to gauge orders of magnitude. Results are broadly similar. Most estimates, even under pessimistic assumptions, suggest that colonial luxuries made consumers better off by about one tenth of final-period consumption – and perhaps more. We cannot confirm these results using highly granular data on individual demand curves as modern-day studies can, but the closest historical analogues also imply welfare gains of 10% or more.

Our quantitative results for tea, sugar, and coffee may well constitute a lower bound on the discoveries’ overall effect. An even wider range of ‘new goods’ arrived on European shores as a result of overseas expansion (Nunn and Qian, 2010). The addition of tomatoes, potatoes, chocolate, exotic spices, polenta, and tobacco transformed consumption habits in even more fundamental ways than sugar, tea, and coffee. If data tracking the rise in consumption of all of these colonial goods were available, welfare increases for European consumers after 1492 as a result of growing variety could be even larger than our findings suggest.

Compared to the gains from new goods today, the welfare increases from introducing sugar, tea, and coffee in the past appear large. In Table 3, we compare the impact of recently invented new goods with our results, including welfare gains from tobacco estimated in the Appendix. Even for the contemporary new goods with the biggest impacts, such as personal computers and the internet, welfare gains pale in magnitude compared with those for colonial goods. Goolsbee and Klenow (2006) calculate a gain of approximately 2% for the internet. Our findings suggest welfare gains that are up to an order of magnitude larger (except when compared with personal computers).26 Other studies of modern-day gains from trade through increasing variety also show smaller increases than the ones we derive. Broda and Weinstein (2006) find welfare gains of 2.2-2.6%, approximately 1/4 of our “best-guess” improvement of 10% from sugar, tea, and coffee alone.


Relatively large gains in the more distant past make sense intuitively: Introducing a new good matters more when the pre-existing range of goods is small. Put another way – adding Apple Cheerios to the range of choices for breakfast cereals has (some) value. However, being able to replace beer soup, porridge and cold cuts with milky, sugary coffee and bread with jam was much nicer, as evidenced by rising budget shares of colonial goods. Exotic new products from the Americas and the Far East – pepper and nutmeg, tea and sugar, coffee and tobacco, chocolate and cloves – improved living standards by far more than modern consumers, sated by an ever-expanding range of new goods, can readily appreciate. The reason why seemingly mundane goods like sugar, coffee and tea probably made a big difference to living standards is that life was not just ‘nasty, brutish, and short’ in Hobbes’ phrase, at their time of introduction – it was also (in culinary terms) boring and bland.

Lower socio-economic status individuals are more active in building up weak ties in the electronic world

Sun, Rui, and Laura Vuillier. 2022. “Socioeconomic Status Predicts Who Initiates and Who Awaits Social Connections.” OSF Preprints. August 12. doi:10.31219/

Abstract: Weak social ties bring people multiple benefits, however, little is known about who initiates social connections that gives rise to weak ties. We propose and tested across 3 studies that socioeconomic status (SES) is a powerful predictor of who initiates or awaits connections with whom, and lower SES individuals are more likely to initiate weak social ties. In Study 1, lower SES individuals reported themselves more likely to initiate and accept Facebook friendship requests. In Study 2, an online dyadic interaction study, people of lower SES were more likely to initiate social connections after a brief chat. In Study 3, across more than 1000 participants, lower SES individuals had more followings (outbound connections) on Twitter, and this result held after controlling hours spent on Twitter and number of followers (inbound connections) on Twitter. Together, we suggested that lower SES individuals are more active in building up weak ties.

Smartphones are considerably more personal and private than PCs, so using them increases private self-focus; making choices using a personal smartphone, compared with a PC, tends to increase the preference for unique & self-expressive options

Phone and Self: How Smartphone Use Increases Preference for Uniqueness. Camilla Eunyoung Song, Aner Sela. Journal of Marketing Research, August 3, 2022.

Abstract: One of the most dramatic shifts in recent years has been consumers’ increased use of smartphones for making purchases and choices, but does using a smartphone influence what consumers choose? This paper shows that, compared with using a personal computer (PC), making choices using a personal smartphone leads consumers to prefer more unique options. The authors theorize that because smartphones are considerably more personal and private than PCs, using them activates intimate self-knowledge and increases private self-focus, shifting attention toward individuating personal preferences, feelings, and inner states. Consequently, making choices using a personal smartphone, compared with a PC, tends to increase the preference for unique and self-expressive options. Six experiments and several replications examine the effects of personal smartphone use on the preference for unique options and test the underlying role of private self-focus. The findings have important implications for theories of self-focus, uniqueness seeking, and technology’s impact on consumers, as well as tangible implications for many online vendors, brands, and researchers who use mobile devices to interact with their respective audiences.

Keywords: smartphones, online shopping, mobile marketing, uniqueness seeking, self-expression, customization, self-focus

Thursday, August 11, 2022

Average TFP growth declined after 1970 due to constraints on idea processing capability, not idea supply, in particular by policies that affect financial market effectiveness

James, Kevin Roger and Kotak, Akshay and Tsomocos, Dimitrios P., Ideas, Idea Processing, and TFP Growth in the US: 1899 to 2019 (July 13, 2022). SSRN:

Abstract: Innovativity - an economy's ability to produce the innovations that drive total factor productivity (TFP)  growth - requires both ideas and the ability to process those ideas into new products and/or techniques. We model innovativity as a function of endogenous idea processing capability subject to an exogenous idea supply constraint and derive an empirical measure of innovativity that is independent of the TFP data itself. Using exogenous shocks and theoretical restrictions, we establish that: i) innovativity predicts the evolution of average TFP growth; ii) idea processing capability is the binding constraint on innovativity; and iii) average TFP growth declined after 1970 due to a constraints on idea processing capability, not idea supply.

Keywords: Innovation, Financial Market Effectiveness, Endogenous Growth, Total Factor Productivity

JEL Classification: O44, O43, O47, O16, O51, O31

V Conclusion

An innovation requires both an exploitable idea and an entrepreneur who transforms that exploitable idea into a new product or process. Innovativity—the economy’s ability to create the innovations that drive TFP growth—is therefore determined by both idea supply and idea processing capability rather than by idea supply alone. Examining US innovativity over the last 120 years, we find that it is plausibly the case that idea processing capability is now and has been the binding constraint on US TFP growth. This finding therefore suggests that idea processing capability plays a central role in the growth process and merits further investigation.
Our innovativity framework creates a new perspective on the debate over the future of economic growth by calling the neo-Malthusian analysis of Gordan (2012, 2014) into question. Starting from the premise that ideas drive TFP growth and the observation that TFP growth has fallen since the Peak regime of 1946/1969, Gordon reaches the seemingly inescapable conclusion that TFP growth is declining because we are running out of ideas. And, if we are running out of ideas, it inevitably follows that “future economic growth may gradually sputter out”(Gordon 2012). Needless to say, the end of growth would have profound and terrible consequences for all aspects of economic, political, and social life.
Our analysis offers a way out of this dismal conclusion. We find that the poor TFP growth performance of the US economy since 1980 is not due a lack of ideas but to a lack of idea processing capability. Our analysis further suggests that the economy’s idea processing capability can be (and has been) influenced by policy, and in particular by policies that a↵ect financial market effectiveness. Consequently, the poor TFP growth performance of the US economy may be due to (cheaply) correctable policy failings rather than to a brute fact of nature that we must simply accept and deal with as best we can.
Our analysis here is exploratory. We focus upon endogenizing idea processing capability in a TFP growth model in which both idea processing capability and idea supply play a central role. To do that, we abstract away from important features of endogenous growth theory. We aim to more fully incorporate these features in future work. It may happen that doing so alters some of the conclusions we reach here. But, given the stakes in the future of growth debate, we should find out.

All over the world, gay men are met with more aversion than gay women; gay men are perceived as mentally unhealthy and more threatening (e.g., more likely to be child molesters)

Sexual Orientation as Gendered to the Everyday Perceiver. P. J. Henry & Russell L. Steiger. Sex Roles, Aug 10 2022.

Abstract: We present an integrated interdisciplinary review of people’s tendency to perceive sexual orientation as a fundamentally gendered phenomenon. We draw from psychology and other disciplines to illustrate that, across cultures and over time, people view and evaluate lesbians, gay men, and bisexuals through how they conform or fail to conform to traditional gender expectations. We divide the review into two sections. The first draws upon historical, anthropological, legal, and qualitative approaches. The second draws upon psychological and sociological quantitative studies. A common thread across these disciplines is that gender and sexual orientation are inseparable constructs in the mind of the everyday social perceiver.

Temporal variations in individuals' religiosity did not predict variations in happiness

Temporal Associations between Religiosity and Subjective Well-Being in a Nationally Representative Australian Sample. Mohsen Joshanloo. The International Journal for the Psychology of Religion, Aug 10 2022.

Abstract: This study examined the between-person and within-person associations between 4 components of subjective well-being (i.e., general life satisfaction, satisfaction with life domains, positive affect, and negative affect) and 2 components of religiosity (i.e., religious salience and religious participation). Data were drawn from the Household, Income, and Labor Dynamics in Australia (HILDA) Survey, collected 5 times between 2004 and 2018. The Random-Intercept Cross-Lagged Panel Model was used to analyze the data. Results showed weak between-person associations between the components of religiosity and subjective well-being. At the within-person level, the cross-lagged associations between religiosity and subjective well-being variables were trivial and nonsignificant. This indicates a lack of robust temporal associations between religiosity and subjective well-being when measured at intervals of a few years.

Higher IQ in adolescence was related to higher openness, lower neuroticism, lower extraversion, lower agreeableness and lower conscientiousness 50 years later

IQ in adolescence and cognition over 50 years later: The mediating role of adult personality. Yannick Stephan et al. Intelligence, Volume 94, September–October 2022, 101682.


• Higher IQ in adolescence was related to better cognition 50 years later.

• Higher IQ was related to higher openness to experience in adulthood.

• Higher openness mediated the link between adolescent IQ and late life cognition.

Abstract: There is substantial evidence for the association between higher early life IQ and better cognition in late life. To advance knowledge on potential pathways, the present study tested whether Five-Factor Model personality traits in adulthood mediate the association between adolescent IQ and later-life cognition. Participants were from the Graduate sample of the Wisconsin Longitudinal Study on Aging (WLS; N = 3585). IQ was assessed in 1957 (about age 17), personality was assessed in 2003–2005 (age = 64), and cognition was assessed in 2011 (age = 71). Controlling for demographic factors, higher IQ in adolescence was related to higher openness, lower neuroticism, lower extraversion, lower agreeableness and lower conscientiousness in adulthood. Higher openness partially mediated the association between higher IQ and better cognition. Additional analyses indicated that the pattern of associations between IQ, personality and cognition was similar when the polygenic score for cognition was included as an additional covariate. Although effect size were small, this study provides new evidence that openness in adulthood is on the pathway between early life IQ and later-life cognition.

Keywords: IQPersonality traitsCognitionMediationLongitudinal study

Wednesday, August 10, 2022

Bonobos were less ready to make coveted fruit juice available to their peers than chimpanzees

Self-interest precludes prosocial juice provisioning in a free choice group experiment in bonobos. Jonas Verspeek, Edwin J. C. van Leeuwen, Daan W. Laméris & Jeroen M. G. Stevens. Primates, Aug 10 2022.

Abstract: Previous studies on prosociality in bonobos have reported contrasting results, which might partly be explained by differences in experimental contexts. In this study, we implement a free choice group experiment in which bonobos can provide fruit juice to their group members at a low cost for themselves. Four out of five bonobos passed a training phase and understood the setup and provisioned fruit juice in a total of 17 dyads. We show that even in this egalitarian group with a shallow hierarchy, the majority of pushing was done by the alpha female, who monopolized the setup and provided most juice to two adult females, her closest social partners. Nonetheless, the bonobos in this study pushed less frequently than the chimpanzees in the original juice-paradigm study, suggesting that bonobos might be less likely than chimpanzees to provide benefits to group members. Moreover, in half of the pushing acts, subjects obtained juice for themselves, suggesting that juice provisioning was partly driven by self-regarding behavior. Our study indicates that a more nuanced view on the prosocial food provisioning nature of bonobos is warranted but based on this case study, we suggest that the observed sex differences in providing food to friends corresponds with the socio-ecological sex difference in cooperative interactions in wild and zoo-housed bonobos.

Courts do not let offenders with multiple personality disorder, which has imperceptibly morphed into dissociative identity disorder, get off the hook

Dissociative Identity Disorder and the Law: Guilty or Not Guilty? Stefane M. Kabene, Nazli Balkir Neftci and Efthymios Papatzikis. Front. Psychol., August 9 2022.

Abstract: Dissociative identity disorder (DID) is a dissociative disorder that gained a significant rise in the past few decades. There has been less than 50 DID cases recorded between 1922 and 1972, while 20,000 cases are recorded by 1990. Therefore, it becomes of great significant to assess the various concepts related to DID to further understand the disorder. The current review has a goal of understanding whether an individual suffering from DID is legally responsible for the committed crime, and whether or not he or she can be considered competent to stand trial. These two questions are to be raised in understanding DID, by first shedding a light on the nature of the disorder and second by examining the past legal case examples. Despite the very nature of the disorder is characterized by dissociative amnesia and the fact that the host personality may have limited or no contact with the alters, there is no consensus within the legal system whether the DID patients should be responsible for their actions. Further to that, courts generally deny the insanity claims for DID suffering patients. In conclusion, more studies in the field are suggested to incorporate primary data into research, as the extensive reliance on secondary data forces us to believe the conclusions that were previously made, and no opportunity to verify those conclusions is present.

Discussion and Analysis

The literature review suggests a general tendency from the courts’ side not to accept the DID propositions and hence exempt the person from the responsibility on the basis of NGRI-DID. The major reasons for the tendency were lack of reliability of scientific methods in diagnosing DID, the possibility of a suspect to malinger DID in such a way that certain specialists will give the desired diagnosis (Ms. Orndorff’s case), the social response to the successful defense based on NGRI-DID, and the immaterial fact of DID, as related to the legal responsibility (the alter in control being sane and competent to stand the trial). Moreover, the case of Maxwell clearly showed that the person can commit the crime again when the society will hardly accept the decision of non-guiltiness. Therefore, the prosecutors tend to find criminals responsible due to the past experience and research done on DID.

The complexity of DID is also supported through the differences in the opinions on the reliability of the tests administered with the purpose of diagnosing DID. It has been suggested by Steinberg that the introduction of Structured Clinical Interview for DSM-III-R (SCID) and the Schedule for Schizophrenia for Affective Disorders and Schizophrenia (SADS) has increased the reliability in diagnosing disorders such as DID (Steinberg et al., 1993). The case of Ms. Orndorff, however, has happened in 2000 and suggests that the diagnostic capabilities in terms of DID were still lacking and hence insufficient to accurately diagnose DID.

As was mentioned before, the courts do have a tendency to deny the NGRI-DID claims for the DID patients that commit crimes. However, it becomes interesting to check on whether similar illnesses, such as epileptic seizures, face the same level of denials in the courts. Epileptic seizures resemble DID in terms of legal responsibility in a way that during a seizure, a person may engage in “actions such as picking at the clothes, trying to remove them, walking about aimlessly, picking up things, or mumbling” (Farrell, 2011b). Of greater importance is the fact that “following the seizure, there will be no memory of it” (Farrell, 2011a). As the actions performed during a seizure are involuntary, the person is unable to appreciate the actions or the consequences that follow, and has no memory of the events, not explained by the regular forgetfulness, the court should consider the person insane at the moment of committing a crime. Farrell elaborates on three cases of successful defenses on the basis of “non-insane automatism” (the definition under which courts nowadays classify epileptic seizures). In all cases, the courts have declared the defendants not guilty of the crimes, as their actions were involuntary, and the defendants had no memory of the events.

It is interesting in the light of above-mentioned cases to see the drastic difference in the courts’ opinions about the similar illnesses in terms of legal responsibility. In both cases, the defendants have no memory of the actions committed. However, it must also be presented that DID patients generally have an identity within them that was aware of the wrongdoing and also carries the memory of that wrongdoing, while under epileptic seizures there is not a single trace that would suggest that the defendant has a memory of a wrongful conduct. One could also argue that while considering the epilepsy-suffering patient, we are concerned with a single identity that is a subject to a biological illness and therefore, it becomes easy to say that the person’s actions were indeed involuntary, while considering the DID, we are talking about totally different identities with their own mindset within a single individual with a very limited information regarding its etiopathology. It means that the court can be reasonably confident in the reliability of epilepsy truly belonging to an individual, while an DID patient can potentially malinger the illness. Even though a few studies have emerged within the last a few years investigating the neurological correlates of DID, the research in this domain is still in the stage of infancy.

Taking a look at the root causes of the DID, it is found that severe psychological trauma or prolonged abuse in the childhood are the most possible reasons that cause the brain to trigger the self-defense mechanisms and protect itself through the dissociation of identities. As the effect of DID is not happening on its own and is occurring following a severe trauma, it should be considered a mental illness and thus be a sufficient reason for claiming the person to be not guilty by the reason of insanity (NGRI-DID). Moreover, both genders can be exposed to any kind of assault or negative experience in the childhood and the tendency of being diagnosed with DID of those victims is correlated. Both men and women showed similar types of identities and behavior that leads to the conclusion that crimes can be done by anybody regardless of their sex (O’Boyle, 1993). Therefore, the framework of how to justify or punish the person who committed wrongdoings should be the same for both male and female.

Many psychiatrists tend to question whether the person is really suffering from DID or trying to pretend in order to have NGRI-DID. However, involving only one specialist might not be enough as we all are human beings and think subjectively based on our past experience and beliefs. The case of Thomas Huskey was advised by the psychiatrist that already had strong beliefs that the murderer is just a great actor, therefore, he did not attempt to search for the root cause of the behavior that was hard to explain at that time (Haliman, 2015). Moreover, involving a few professionals is no longer enough since the opinion can differ based on individual observation, however, even the final judgment can be affected by groupthink. Based on the case of Ms. Moore, it was easier to find her guilty since both identities were directly involved in the action, so even the presence of other minor identities would not justify her wrongdoings. In particular, she was not even diagnosed with DID during the trial and was found responsible regardless of her mental illness (Moore, 1988).

Regarding the doubts over the reliability of measures for the assessment of DID, there are so far very few mechanisms available to psychiatrists that can be used in an attempt to evaluate patient’s dissociative disorders. It has been found that the long interviews used during the evaluation allow for emerging of different identities present within an individual. The long aspect of the interviews and evaluation also reduce the possibility of patient malingering the diagnosis. Kluft (1999) stated that “simulated DID presents crude manifestations of the disorder, such as stereotypical good/bad identity states and a preoccupation with the circumstances individual hopes to avoid by obtaining an DID diagnosis.” Kluft also suggested that it is difficult for the individual to maintain the voice, set of body gestures, and memory for every personality that he or she is trying to simulate. Hence, it can be suggested that the actual possibility of malingering DID is extremely challenging, and that cases of malingered DID will be very rare compared to correctly diagnosed DID.

Speaking of suggesting the framework for deciding on person’s liability on the basis of DID, the diagnosis has proven itself to be so complex that no universal method can actually be applied. However, there is a set of actions that should be done in order to assess the responsibility for the crime committed. Initially, an evaluation of the patient should be performed by several independent psychiatrists. The DID in our opinion should only be considered valid when all the psychiatrists involved agree on the opinion that the defendant is suffering from DID. Based on the diagnosis, the question of competency to stand trial must be answered. Then, the court should select the appropriate method for assessing the responsibility. The “host-alter” method is best when there is a dominant personality present, and the crime was committed by the alter identity. The “alter-in-control” method should be used when there is no clear evidence of the dominant identity. If the method used provides a result that supports the fact that the identity evaluated is insane at the time of committing a crime, the defendant should be considered not guilty.

No structural brain differences as a function of the Big Five personality traits from a systematic review and meta-analysis

"Nothing to see here": No structural brain differences as a function of the Big Five personality traits from a systematic review and meta-analysis. Yen-Wen Chen, Turhan Canli. Personality Neuroscience, Volume 5, Aug 9 2022.

Abstract: Personality reflects social, affective, and cognitive predispositions that emerge from genetic and environmental influences. Contemporary personality theories conceptualize a Big Five Model of personality based on the traits of neuroticism, extraversion, agreeableness, conscientiousness, and openness to experience. Starting around the turn of the millennium, neuroimaging studies began to investigate functional and structural brain features associated with these traits. Here, we present the first study to systematically evaluate the entire published literature of the association between the Big Five traits and three different measures of brain structure. Qualitative results were highly heterogeneous, and a quantitative meta-analysis did not produce any replicable results. The present study provides a comprehensive evaluation of the literature and its limitations, including sample heterogeneity, Big Five personality instruments, structural image data acquisition, processing, and analytic strategies, and the heterogeneous nature of personality and brain structures. We propose to rethink the biological basis of personality traits and identify ways in which the field of personality neuroscience can be strengthened in its methodological rigor and replicability.


3. Discussion

MRI studies have come under criticism for reporting under-powered and non-replicable findings (Button et al., Reference Button, Ioannidis, Mokrysz, Nosek, Flint, Robinson and Munafò2013; Szucs & Ioannidis, Reference Szucs and Ioannidis2017). Here, we used a systematic review and a meta-analysis approach to discern which findings, if any, would replicate reported associations between personality and brain measures. Surprisingly, we found no evidence for robust associations between any of the Big Five traits and brain structural indices (i.e., GMV, CT, and SA). Although we observed some consistent results from the qualitative systematic review, these findings failed confirmation when we used a quantitative meta-analytic approach.

3.1. Comparison with previous systematic review and/or meta-analysis studies

To our knowledge, only three studies used a systematic review and/or quantitative meta-analytic approach to evaluate the replicability of associations between personality traits and brain structural indices. One meta-analysis (Mincic, Reference Mincic2015) examined the association between GMV and a broad composite meta-trait named “negative emotionality” and included studies that measured one of these traits: Behavioral inhibition, harm avoidance, trait anxiety, or neuroticism.

Two other studies restricted their analyses to single “Big Five” traits only. One review by Montag, Reuter and colleague (Reference Montag, Reuter, Jurkiewicz, Markett and Panksepp2013) focused on GMV and neuroticism. These investigators reported heterogeneous findings across studies but noted consistent negative associations with neuroticism in prefrontal regions that included SFG and MFG and the OFC. This observation is consistent with our systematic review. However, Montag and colleagues did not subject their reviewed studies to a quantitative meta-analysis to determine the robustness of this observation, whereas our meta-analysis failed to confirm this observed association.

The second study was conducted by Lai et al. (Reference Lai, Wang, Zhao, Zhang, Yang and Gong2019) to examine the association between GMV and extraversion, using both a systematic review and meta-analytic approach. Based on quantitative meta-analysis, these investigators reported positive associations in the medOF and PRC, and negative associations in PHC, SMG, ANG, and MFG. The results contradicted our null meta-analysis result for extraversion. The discrepancies might derive from, first, the difference in the studies that were included across the two meta-analyses. First, Lai et al. (Reference Lai, Wang, Zhao, Zhang, Yang and Gong2019) only included VBM studies, whereas the present study included both VBM (n = 14) and SBM (n = 4) studies. Thus, four studies using SBM were not included in Lai et al. (Reference Lai, Wang, Zhao, Zhang, Yang and Gong2019). Second, Grodin and White (Reference Grodin and White2015) were excluded from the present study due to the personality instrument this study used. This study used two subscales (Social Potency and Social Closeness) from the Multidimensional Personality Questionnaire Brief Form as proxy of extraversion. However, we determined that this instrument does not align with the same conceptual structure of the global extraversion of the Big Five and therefore excluded this study. Third, two studies that used different image processing were by DeYoung et al. (Reference DeYoung, Hirsh, Shane, Papademetris, Rajeevan and Gray2010) (which did not perform segmentation in the preprocessing) and by Yasuno et al. (Reference Yasuno, Kudo, Yamamoto, Matsuoka, Takahashi, Iida and Kishimoto2017) (which used a T1w/T2w ratio signal), and were not included in Lai et al. (Reference Lai, Wang, Zhao, Zhang, Yang and Gong2019). In addition, Nostro et al. (Reference Nostro, Müller, Reid and Eickhoff2017), which was included in Lai et al. (Reference Lai, Wang, Zhao, Zhang, Yang and Gong2019), were excluded from the present study due to non-independent samples overlapping with another larger study (Owens et al., Reference Owens, Hyatt, Gray, Carter, MacKillop, Miller and Sweet2019). The second difference between the present study and Lai et al. (Reference Lai, Wang, Zhao, Zhang, Yang and Gong2019) is the meta-analytic software versions used. Lai et al. (Reference Lai, Wang, Zhao, Zhang, Yang and Gong2019) used the previous version of SDM, Anisotropy Effect-Size Seed-based d Mapping (AES-SDM) (Radua et al., Reference Radua, Mataix-Cols, Phillips, El-Hage, Kronhaus, Cardoner and Surguladze2012Reference Radua, Rubia, Canales-Rodríguez, Pomarol-Clotet, Fusar-Poli and Mataix-Cols2014), whereas the present study used the latest version, SDM-PSI. The major improvement of SDM-PSI is the implementation of multiple imputations of study images to avoid the bias from the single imputation and a less biased estimation of population effect size, and it is considered more robust than AES-SDM (Albajes-Eizagirre, Solanes, Vieta, et al., Reference Albajes-Eizagirre, Solanes, Vieta and Radua2019).

3.2. Possible explanations of heterogeneous findings

Several possible explanations may account for discrepancies across the studies, including, but not limited to, (1) sample heterogeneity, (2) Big Five personality instruments, (3) structural image data acquisition, processing, and analytic strategies, (4) statistical approach and statistical significance threshold, and (5) the heterogeneous nature of personality and brain structure. The following sections discuss the above-listed factors in greater detail.

3.2.1. Sample heterogeneity

Sample characteristics that potentially contribute to highly heterogeneous results across the literature include mean age and age range, sex, and the inclusion of patient cohorts and different levels of personality traits across samples. Age

From the systematic review, age correlated negatively with neuroticism, extraversion, and openness, but positively with agreeableness (note that not all studies that examined association between age and personality traits reported significant associations, as shown in Table S18). Those qualitative observations are consistent with previous population-based cross-sectional and mean-level studies (Allemand et al., Reference Allemand, Zimprich and Hertzog2007; Donnellan & Lucas, Reference Donnellan and Lucas2008). We examined whether age could account for heterogeneous meta-analysis results for all five traits using meta-regression, but we did not observe any significant age effect on any of the meta-analyses for five traits. However, the lack of a significant effect may be due, in part, to a narrow age range across the samples, which mainly consisted of adults aged 18 – 40 (Figure 4). This may hinder the generalizability of the results. Only one study (Nickson et al., Reference Nickson, Chan, Papmeyer, Romaniuk, Macdonald, Stewart and Whalley2016) examined longitudinal changes of personality traits and two studies (Nickson et al., Reference Nickson, Chan, Papmeyer, Romaniuk, Macdonald, Stewart and Whalley2016; Taki et al., Reference Taki, Thyreau, Kinomura, Sato, Goto, Wu and Fukuda2013) examined longitudinal changes of GMV. Nickson et al. (Reference Nickson, Chan, Papmeyer, Romaniuk, Macdonald, Stewart and Whalley2016) observed no association between AMY GMV changes and neuroticism and extraversion changes over an average of two-year interval among a mixed sample of patients with major depressive disorder and healthy controls. However, considering the small-to-moderate sample size and heterogeneous composition of the sample, future research with longitudinal study design is required to explore the causal relationship between age, personality traits, and brain structures. Furthermore, none of the included studies considered non-linear associations between age and personality traits, despite evidence in support of such a relation (Donnellan & Lucas, Reference Donnellan and Lucas2008; Terracciano et al., Reference Terracciano, McCrae, Brant and Costa2005). For example, a curvilinear association was reported between age and conscientiousness, such that the highest scores were observed in middle adulthood (Donnellan & Lucas, Reference Donnellan and Lucas2008). Future research with the consideration of non-linear nature of age and personality traits is required to delineate the relationship.

Figure 4. Sample Mean Age and Age Range Distribution of Studies Included in the Systematic Review and Meta-analysis across Big Five Personality Traits and Three Brain Indices. Note. The study (y-axis) was ordered by the mean age (dot) from each study. Studies were separately labeled as “(hc)/(pt)/(hc/pt)” indicating results from the given study were reported separately for healthy and patient groups or combining healthy and patient groups. Not all studies provided the information for mean age or age range, thus, data from those studies were presented incompletely or not presented. Two red dashed vertical lines indicating the age of 18 and 65 Sex

From our systematic review, females reported higher levels of personality measures across all five traits, with the exception of extraversion from Omura et al. (Reference Omura, Constable and Canli2005) and openness from Gray et al. (Reference Gray, Owens, Hyatt and Miller2018) (note that not all studies that examined sex difference in personality traits reported significant difference, as shown in Table S19), and this observation is consistent with a previous population-based cross-sectional study (Soto et al., Reference Soto, John, Gosling and Potter2011). Interestingly, we observed that the mean ages of the participants were younger in Omura et al. (Reference Omura, Constable and Canli2005) and Gray et al. (Reference Gray, Owens, Hyatt and Miller2018), compared to other studies that reported higher levels of extraversion and openness in females. This observation is also partially consistent with the observations from Soto et al. (Reference Soto, John, Gosling and Potter2011), which showed that, on average, sex differences in personality traits vary across difference ages. Among all included studies in the systematic review (across five traits and three brain indices), 14 studies examined sex-dependent associations between the Big Five and brain structure. Two main approaches were used, including conducting trait–brain analysis separately for females and males and conducting sex-by-trait interaction analysis. As summarized in the previous section, the results are inconsistent across those studies, such that some studies reported trait–brain associations only in females (Hu et al., Reference Hu, Erb, Ackermann, Martin, Grodd and Reiterer2011), only in males (Hu et al., Reference Hu, Erb, Ackermann, Martin, Grodd and Reiterer2011; Montag, Eichner, et al., Reference Montag, Eichner, Markett, Quesada, Schoene-Bake, Melchers and Reuter2013; Nostro et al., Reference Nostro, Müller, Reid and Eickhoff2017), or in neither group (Knutson et al., Reference Knutson, Momenan, Rawlings, Fong and Hommer2001; Liu et al., Reference Liu, Weber, Reuter, Markett, Chu and Montag2013; Wright et al., Reference Wright, Williams, Feczko, Barrett, Dickerson, Schwartz and Wedig2006Reference Wright, Feczko, Dickerson and Williams2007), and interaction analyses produced similarly conflicting results ((Blankstein et al., Reference Blankstein, Chen, Mincic, McGrath and Davis2009; Cremers et al., Reference Cremers, van Tol, Roelofs, Aleman, Zitman, van Buchem and van der Wee2011; Sweeney et al., Reference Sweeney, Tsapanou and Stern2019versus (Bjørnebekk et al., Reference Bjørnebekk, Fjell, Walhovd, Grydeland, Torgersen and Westlye2013; J. C. Gray et al., Reference Gray, Owens, Hyatt and Miller2018; Lewis et al., Reference Lewis, Dickie, Cox, Karama, Evans, Starr and Deary2018; Wang et al., Reference Wang, Zhao, Li, Wang, Luo and Gong2019)). We then examined whether sex (using the proportion of females) could account for heterogeneous meta-analysis results for all five traits using meta-regression, but again we did not observe significant effects. The potential explanations for sex difference include sex-related hormonal variability (De Vries, Reference De Vries2004), early biological and social developmental trajectory (Blankstein et al., Reference Blankstein, Chen, Mincic, McGrath and Davis2009; Goldstein et al., Reference Goldstein, Seidman, Horton, Makris, Kennedy, Caviness and Tsuang2001), and social processing differences in response to the environment (Wager et al., Reference Wager, Phan, Liberzon and Taylor2003). However, due to the mixed results from the literature, future research should take sex difference into account when examining the association between personality traits and brain structures. Inclusion of patient cohorts and different levels of personality traits across samples

From the systematic review studies (across five traits and three brain indices), 14 studies included patient cohorts, as summarized in Table S17. Most studies reported higher mean level of neuroticism and lower mean level of extraversion and conscientiousness in patient cohorts, compared to healthy individuals (note that not all studies reported group differences in these three traits, as shown in Table S17), whereas no mean-level differences were reported for agreeableness and openness. Among those 14 patient cohort studies, three studies reported group differences in trait–brain associations, noting opposite associations between patients and healthy participants. It is possible that different levels of personality traits between patient and healthy groups contribute to the conflicting trait–brain associations. For example, a higher mean level of neuroticism was observed among patients with alcohol use disorder, compared to healthy participants (Zhao et al., Reference Zhao, Zheng and Castellanos2017). However, no group mean-level difference was observed in Nair et al. (Reference Nair, Beniwal-Patel, Mbah, Young, Prabhakaran and Saha2016) and Moayedi et al. (Reference Moayedi, Weissman-Fogel, Crawley, Goldberg, Freeman, Tenenbaum and Davis2011). Alternative explanations include symptoms associated with the given medical or psychiatric conditions and brain structural differences underlying those conditions. To remove the potential effect from patient cohorts for meta-analysis, we conducted a sub-group meta-analysis excluding patient cohort studies and the result from neuroticism (this is the only trait that with patient cohort study in meta-analysis) remained unchanged.

Considering the potential influence of levels of personality traits across studies among non-patient studies, we compared the mean scores of personality trait measures among systematic review studies that reported contradictory associations. For example, two included studies reported associations in opposite directions between openness and PCC GMV, with higher mean level of openness reported in Yasuno et al. (Reference Yasuno, Kudo, Yamamoto, Matsuoka, Takahashi, Iida and Kishimoto2017) compared to Kitamura et al. (Reference Kitamura, Yasuno, Yamamoto, Kazui, Kudo, Matsuoka and Kishimoto2016). On the other hand, another two studies that reported associations in opposite directions between extraversion and MFG GMV reported comparable mean-level extraversion scores (Blankstein et al., Reference Blankstein, Chen, Mincic, McGrath and Davis2009; Coutinho et al., Reference Coutinho, Sampaio, Ferreira, Soares and Gonçalves2013). However, due to differences in personality trait instruments and scoring methods (e.g., some studies reported raw score, whereas some studies reported T scores), lacking reporting of personality scores in some studies, it is difficult to determine whether the levels of personality traits might play a role in conflicting results we observed from the included studies.

3.2.2. Heterogeneity in big five trait instruments

The use of different personality trait instruments might contribute to discrepancies across included studies. The most commonly used instruments were the Neuroticism, Extraversion, Openness Personality Inventory – Revised (NEO-PI-R) and the NEO-Five-Factor Inventory (NEO-FFI, short version of NEO-PI-R). Other instruments included the International Personality Item Pool (IPIP), Eysenck Personality Questionnaire (EPQ), Big Five Inventory (BFI), Big Five Structure Inventory (BFSI), Big Five Aspects Scale (BFAS), and 16 Personality Factor test (16 PF). Although studies showed high correlations between different instruments, some trait scales showed only low-to-moderate correlations (Gow et al., Reference Gow, Whiteman, Pattie and Deary2005). We examined whether the use of different instruments (NEO versus non-NEO) could account for heterogeneous meta-analysis results using sub-group analysis with only studies using NEO (either NEO-PI-R or NEO-FFI), but we did not observe significant results for all five traits. In addition, all the instruments listed were self-report questionnaires. Studies suggested combined observation- and interview-based, informant report (Connolly et al., Reference Connolly, Kavanagh and Viswesvaran2007; Hyatt et al., Reference Hyatt, Owens, Gray, Carter, MacKillop, Sweet and Miller2019) or to use physiological responses (Taib et al., Reference Taib, Berkovsky, Koprinska, Wang, Zeng and Li2020) to better capture the complex construct of personality and avoid the bias from self-report.

3.2.3. Heterogeneity in structural image data acquisition, processing, and analytic strategies

The heterogeneities of the structural image data acquisition, (pre)processing, and analytic strategies may also have contributed to discrepancies across studies. Structural image data acquisition and processing

The use of different MRI scanners, scanner magnetic field strength, voxel size, and smoothing kernel could result in differences in image spatial resolution and signal-to-noise ratio. In addition, the use of VBM versus SBM processing methods might lead to inconsistent results. Although Kunz et al. (Reference Kunz, Reuter, Axmacher and Montag2017) reported highly correlated total GMV results between VBM and SBM processing methods, none of the included studies directly compared VBM and SBM for regional structural results. However, the small number (18 VBM and 5 SBM studies across five traits) of studies we could include in the meta-regression limits any strong conclusions. Structural image data analytic approaches

Different levels of structural analysis, whole-brain versus region-of-interest (ROI), could contribute to the heterogeneous results. Note that only studies using whole-brain voxel-/vertex-wise analysis and the same threshold across the whole brain were included in the meta-analysis to avoid the bias derived from regions with more liberal threshold (i.e., a prior ROI analysis) (Albajes-Eizagirre, Solanes, Fullana, et al., Reference Albajes-Eizagirre, Solanes, Fullana, Ioannidis, Fusar-Poli, Torrent and Radua2019; Q. Li et al., Reference Li, He, Zhuang, Wu, Sun, Wei and Qiu2020), which makes a direct comparison between whole-brain and ROI studies difficult. Li et al. (Reference Li, Yan, Li, Wang, Li, Li and Li2017) made a direct comparison between whole-brain vertex-wise and whole-brain regional parcellation-based analyses and reported inconsistent results (i.e., different traits were associated with different brain indices in different regions) from the same group of participants. The authors suggested that the two approaches provide different advantages, such that vertex-wise approach could potentially give more accurate localizations, whereas parcellation-based approach could potentially achieve higher test-retest reliability across populations/studies. Furthermore, the selection of the atlas to label brain region for a given peak coordinates (for whole-brain voxel-/vertex-wise studies) or to extract mean value for pre-defined ROIs (for ROI studies) adds another layer of heterogeneity, as the same voxel/vertex coordinates may be labeled differently across atlases. Atlas used by the included studies can be found in Supplementary Tables S2 - S16. Future research should utilize alternative approaches, such as voxel-/vertex-based and parcellation-based approaches, to evaluate the reliability of the results.

The present study was limited to studies examining brain structure using T1-weighted structural MRI. Alternatively, brain structure can be measured by diffusion MRI. By measuring diffusivity of the water molecules, diffusion imaging allows an indirect way to measure white matter fiber structure (Mori & Zhang, Reference Mori and Zhang2006) and it has been implemented in the field of personality neuroscience (e.g., Avinun et al., Reference Avinun, Israel, Knodt and Hariri2020; Bjørnebekk et al., Reference Bjørnebekk, Fjell, Walhovd, Grydeland, Torgersen and Westlye2013; Privado et al., Reference Privado, Román, Saénz-Urturi, Burgaleta and Colom2017; Ueda et al., Reference Ueda, Kakeda, Watanabe, Sugimoto, Igata, Moriya and Korogi2018; Xu & Potenza, Reference Xu and Potenza2012). Furthermore, beyond single voxel/vertex and single parcellated region, connectome and network approaches may offer promising alternative ways to investigate patterns of brain structures and their associations with personality (Markett et al., Reference Markett, Montag and Reuter2018). Network approaches not only measure characteristics of nodes (brain regions) and edges (connections between brain regions) within and between the brain networks but also measure the local and global organization of the brain networks (Sporns & Zwi, Reference Sporns and Zwi2004). An optimal connectome approach may be achieved by implementing both high-resolution structural and diffusion MRI images (Gong et al., Reference Gong, He, Chen and Evans2012; Sporns et al., Reference Sporns, Tononi and Kötter2005).

3.2.4. Heterogeneity in statistical approach and statistical significance threshold

The use of different statistical approaches and statistical significance thresholds might contribute to discrepancies across studies. Covariates in model specification

For model specification, commonly used covariates include age, sex, and global brain indices. Among the included studies in the systematic review (across five traits and three brain indices), covariates included age (n = 55 studies), sex (n = 47), TGMV/mean CT (n = 13), total brain volume (TBV) (n = 9), intracranial volume (ICV) (n = 26). Other covariates included intelligence (n = 7) and education (n = 3). Studies have directly examined influence of the covariates and suggested that the associations between personality traits and brain structures change dramatically (Hu et al., Reference Hu, Erb, Ackermann, Martin, Grodd and Reiterer2011; Hyatt et al., Reference Hyatt, Owens, Crowe, Carter, Lynam and Miller2020). For example, Hu et al. (Reference Hu, Erb, Ackermann, Martin, Grodd and Reiterer2011) reported different trait–GMV associations when controlling for different combinations of age, sex, and TGMV, and Hyatt et al. (Reference Hyatt, Owens, Crowe, Carter, Lynam and Miller2020) reported remarked changes from the inclusion of ICV as covariate in statistical significance of the relation between various psychological variables (e.g., personality, psychopathology, cognitive processing) and regional GMV. In addition to demographic covariates, some studies also controlled for other personality traits (n = 15 across five traits among systematic review studies). Statistically speaking, the “unique association” of a given trait by including the other traits as covariates seemed to be reasonable, but whether the inclusion of other traits as covariates is still under debate, as some studies argued that the interpretation of “partial association” might not be straightforward (Lynam et al., Reference Lynam, Hoyle and Newman2006; Sleep et al., Reference Sleep, Lynam, Hyatt and Miller2017) and might fail to capture the inter-correlations between personality traits (e.g., Gray et al., Reference Gray, Owens, Hyatt and Miller2018; Holmes et al., Reference Holmes, Lee, Hollinshead, Bakst, Roffman, Smoller and Buckner2012; Liu et al., Reference Liu, Weber, Reuter, Markett, Chu and Montag2013). Profile- or cluster-based approaches have been proposed as an alternative way to capture the inter-dependency of personality traits (e.g., Gerlach et al., Reference Gerlach, Farb, Revelle and Nunes Amaral2018; Y. Li et al., Reference Li, He, Zhuang, Wu, Sun, Wei and Qiu2020; Mulders et al., Reference Mulders, Llera, Tendolkar, van Eijndhoven and Beckmann2018). To assess whether the inclusion of different covariates could account for heterogeneous meta-analysis results, we conducted a series of meta-regression analyses with the inclusion of (1) ICV, (2) TGMV, (3) any global brain indices (ICV, TGMV, or TBV), (4) other personality traits as covariates, and (5) the total number of covariates. Our results did not change as a function of any of these variables, although this may also reflect the small number of studies that fulfilled relevant selection criteria. We suggest that future research and future synthesis work should take the inclusion of covariates into account. Significance threshold and multiple comparison correction

The choice of statistical significance threshold for reporting results should also be considered. Various levels of threshold were used among the included studies, including uncorrected versus corrected for multiple comparison, voxel-/vertex-level versus cluster-level correction, and different multiple comparison correction methods (e.g., family-wise error, Monte Carlo simulated, non-stationary, false discovery rate). Meta-analytic null results from this study may be due, in part, to positive results from studies that applied liberal statistical thresholds to data with small effect sizes, which were not robust enough to be replicable.

3.2.5. Heterogeneous nature of personality and brain structure Replication challenges

Direct replication efforts in studies of personality and brain structure remain scarce to date. Replication was directly assessed in Owens et al. (Reference Owens, Hyatt, Gray, Carter, MacKillop, Miller and Sweet2019) by comparing results with their earlier study (Riccelli et al., Reference Riccelli, Toschi, Nigro, Terracciano and Passamonti2017), using data from the same dataset (i.e., HCP). Owens et al. (Reference Owens, Hyatt, Gray, Carter, MacKillop, Miller and Sweet2019) demonstrated that not all results were replicated from the replication sample or the full sample. The sample characteristics, personality and image data acquisition, and processing were almost identical across those two studies, suggesting that other explanations than differences in sample characteristic and methodologies should be considered, according to Owens et al. (Reference Owens, Hyatt, Gray, Carter, MacKillop, Miller and Sweet2019). Heterogeneous nature and individual difference

Finally, we consider the complex and heterogeneous nature of both personality and brain structures. First, a large number of brain regions were reported to be associated with one or more personality traits, and this observation might suggest that personality is constructed by many small effects from different brain regions (M. Li et al., Reference Li, Wei, Yang, Zhang and Qiu2019; Montag, Reuter, et al., Reference Montag, Reuter, Jurkiewicz, Markett and Panksepp2013; Owens et al., Reference Owens, Hyatt, Gray, Carter, MacKillop, Miller and Sweet2019). Second, most conclusions from the literature were drawn from group mean levels, which ignored individual differences. Studies have demonstrated the influences of individual differences on cross-sectional and longitudinal changes in personality traits (Allemand et al., Reference Allemand, Zimprich and Hertzog2007; Lüdtke et al., Reference Lüdtke, Trautwein and Husemann2009). Both genetic and environment factors have been suggested to contribute to the heterogeneities. For example, heritability of personality and regional brain structures has been suggested to contribute to heterogeneous associations between the two (Nostro et al., Reference Nostro, Müller, Reid and Eickhoff2017; Valk et al., Reference Valk, Hoffstaedter, Camilleri, Kochunov, Yeo and Eickhoff2020). On the other hand, ample research has also demonstrated that both personality and brain structure are susceptible to change by the environment and experiences (e.g., Montag, Reuter, et al., Reference Montag, Reuter, Jurkiewicz, Markett and Panksepp2013; Roberts & Mroczek, Reference Roberts and Mroczek2008). Third, considering the highly heterogeneous nature and individual differences shaped by genetic and environment in personality traits, it is also possible that the global dimension of the Big Five personality traits is too broad to have the universal representation in the brain. Based on NEO-PI-R (Costa & McCrae, Reference Costa and McCrae1992), each of the five personality traits is constructed by six facets. Studies have demonstrated that some trait facets contribute stronger, relative to the remaining facets for a given global trait, to the association between a certain global trait and brain structure (Bjørnebekk et al., Reference Bjørnebekk, Fjell, Walhovd, Grydeland, Torgersen and Westlye2013; M. Li et al., Reference Li, Wei, Yang, Zhang and Qiu2019). However, only a few studies included in the systematic review conducted additional facet analysis. Future research is recommended to examine the facets and variances of personality traits and brain structures and studies with regular follow-up are needed to evaluate the longitudinal changes. Considerations of statistical approach and power

The highly heterogeneous nature of personality and brain structure also raises the concern of statistical power of the previous literature to detect reliable associations between psychological phenotype and brain structure (Masouleh et al., Reference Masouleh, Eickhoff, Hoffstaedter and Genon2019). An important aspect of statistical power relates to the image data analytic approach used. Although a voxel- or vertex-based approach could potentially provide more precise localization (T. Li et al., Reference Li, Yan, Li, Wang, Li, Li and Li2017), this also raises the concern of overestimating the statistical effect based on a peak voxel/vertex (Allen & DeYoung, Reference Allen, DeYoung and Widiger2017; DeYoung et al., Reference DeYoung, Hirsh, Shane, Papademetris, Rajeevan and Gray2010). On the other hand, with the advantage of improving signal-to-noise ratio, improving test-retest reliability, and reducing the number of variables, the use of whole-brain parcellation-based approach has been increased (e.g., Eickhoff et al., Reference Eickhoff, Constable and Yeo2018; Hyatt et al., Reference Hyatt, Owens, Gray, Carter, MacKillop, Sweet and Miller2019; T. Li et al., Reference Li, Yan, Li, Wang, Li, Li and Li2017). Future research should carefully weigh the advantages and limitations of different image analytic approaches and possibly report on the congruency of their findings across multiple analysis methodologies.

3.3. Does a meaningful relation between the big five and brain structure really exist?

Having addressed several plausible factors contributing to heterogeneous findings and replication failure, we also consider the possibility that there is no meaningful relation between the Big Five personality traits and brain structure. Indeed, consistent null-to-very-small associations between the Big Five personality and brain structures have been reported by recent large-scale studies with over 1,100 participants (Avinun et al., Reference Avinun, Israel, Knodt and Hariri2020; Gray et al., Reference Gray, Owens, Hyatt and Miller2018). For example, Avinun et al. (Reference Avinun, Israel, Knodt and Hariri2020) investigated both global and facet levels of Big Five personality with structural indices from whole-brain parcellation (cortical CT, cortical SA, and subcortical GMV) and reported only conscientiousness (R 2  = .0044) (and its dutifulness facet (R 2  = .0062)) showed a small association with regional SA in superior temporal region. A recent study by Hyatt et al. (Reference Hyatt, Sharpe, Owens, Listyg, Carter, Lynam and Miller2021) of different levels of personality (from meta-traits, global Big Five traits, facets, and individual NEO-FFI items) and different levels of structural measures (from global brain measures to regional cortical and subcortical parcellations) reported that even the largest association (between Intellect facet of openness and global brain measures) yielded a mean effect size that was less than .05 (estimated by R 2 ). As we discussed above, alternative ways to assess brain structural features, such as connectome and network approaches, exist, and these may be better suited to map correspondences to complex traits than traditional approaches.

Our review of the literature was limited to studies of the Big Five personality model, which emerged from lexical analyses. The model serves the descriptive purpose but is not necessary explanatory (Deyoung & Gray, Reference Deyoung, Gray, Corr and Matthews2009; Montag & Davis, Reference Montag and Davis2018). Thus, there is no a priori reason why these constructs should map neatly onto biological systems, although the Big Five traits are associated with biologically based constructs such as Gray’s Reinforcement Sensitivity Theory (RST) and Behavioral Inhibition and Approach System (BIS/BAS) (McNaughton & Corr, Reference McNaughton and Corr2004), Panksepp’s Affective Neuroscience Theory (ANT) (Montag et al., Reference Montag, Elhai and Davis2021; Montag & Davis, Reference Montag and Davis2018), and the dimensions of extraversion and neuroticism in Eysenck’s model (Eysenck, Reference Eysenck1967). For example, Vecchione and colleagues (Reference Vecchione, Ghezzi, Alessandri, Dentale and Corr2021), applied a latent-variable analysis approach to a sample of 330 adults who completed both Carver and White’s BIS/BAS and the Big Five Inventory. These authors found that BIS correlated with emotional stability (inverse of neuroticism) and that BAS correlated with extraversion, after controlling for higher-order factors. Moreover, Montag and Panksepp (Reference Montag and Panksepp2017) demonstrated that seven ANT primary emotional systems are respectively associated with at least one global dimension of the Big Five, such as FEAR, ANGER, and SADNESS with neuroticism, PLAY with extraversion, CARE and ANGER with agreeableness, and SEEKING with openness. Considering that Big Five model closely maps onto biological motivational and emotional systems, future work should include side-by-side comparisons and integrate across conceptual models of personality structure (such as Big Five, RST, and ANT) to provide a comprehensive picture of personality. This could be an iterative process by which future personality models would continue to be refined by neural data and guide the next generation of imaging and other biological (e.g., genetic) studies.

3.4. Limitations

Some limitations should be noted when interpreting the present systematic review and meta-analysis results. First, one of the major challenges of meta-analysis is the trade-off between meta-analysis power and homogeneity of the included studies (Müller et al., Reference Müller, Cieslik, Laird, Fox, Radua, Mataix-Cols and Eickhoff2018). Although no study, to our knowledge, has empirically evaluated the minimal number of studies required for meta-analysis using SDM, Eickhoff et al. (Reference Eickhoff, Nichols, Laird, Hoffstaedter, Amunts, Fox and Eickhoff2016) suggested that between 17 to 20 studies are required to achieve adequate power using activation likelihood estimator (ALE) meta-analysis, although whether this result is transferrable to SDM meta-analysis remains to be determined. From the present meta-analysis for five personality traits and GMV studies, we maximized the number of studies by including heterogeneous studies such that studies with patient cohorts, measuring GMD, using T1w/T2w ratio signals, and so on, and we demonstrated that the results remained unchanged with more homogeneous sub-group meta-analysis by excluding the abovementioned studies. Second, the present meta-analysis results were derived from the reported peaks, rather than raw data, and this limits our evaluation of variability within each individual study. Lastly, the present review only included peer-reviewed articles. “Grey literature,” which refers to studies not captured by traditional database and/or commercial publishers, should be also considered to avoid bias when synthesizing the literature (Cooper et al., Reference Cooper, Hedges and Valentine2009). Previous review has found that the peer-reviewed published works had average greater effects and more significant results, compared to unpublished works like theses and dissertations (McLeod & Weisz, Reference McLeod and Weisz2004; Webb & Sheeran, Reference Webb and Sheeran2006). It is therefore unlikely that our general conclusions of lacking associations between the Big Five and structural brain measures would be altered by the inclusion of unpublished studies. Future researchers are encouraged to include studies from various sources and to carefully evaluate the quality of all works to provide reliable review.

3.5. Implication and conclusion

To our knowledge, this is the first study to systematically evaluate the entire published literature of the association between the Big Five personality traits and three brain structural indices, using a combination of qualitative and quantitative approaches. Qualitative results suggested highly heterogeneous findings, and the quantitative results found no replicable results across studies. Our discussion pointed out methodological limitations, the dearth of direct replications, as well as gaps in the extant literature, such as limited data on trait facets, on brain-personality associations across the life span, and on sex differences.

When it comes to the relation of Big Five personality and structural brain measures, the field of Personality Neuroscience may have come to a crossroads. In fact, the challenge of finding meaningful and replicable brain–behavior relations is not unique to Big Five personality traits. The same challenge has also emerged in other psychological constructs, including, but not limited to, intelligence and cognition (e.g., attention, executive function), psychosocial processes (e.g., political orientation, moral), and psychopathology (e.g., anxiety, internalizing, externalizing) (Boekel et al., Reference Boekel, Wagenmakers, Belay, Verhagen, Brown and Forstmann2015; Genon et al., Reference Genon, Wensing, Reid, Hoffstaedter, Caspers, Grefkes and Eickhoff2017; Marek et al., Reference Marek, Tervo-Clemmens, Calabro, Montez, Kay, Hatoum and Dosenbach2020; Masouleh et al., Reference Masouleh, Eickhoff, Hoffstaedter and Genon2019). On the one hand, the lack of any significant associations discourages further efforts down this path, as resources may be better spent on following other leads. On the other hand, we suggested several ways to strengthen future work investigating personality–brain structure associations. Consilience may be attained by parallel processing: Expanding upon next-generation structural imaging and analysis approaches, while developing new models of personality informed by cutting-edge data prescribing biological constraints. This may be best accomplished by coming to a consensus as a field on how we can best strengthen methodological rigor and replicability and creating an incentive structure that rewards large-scale consortia building in parallel to smaller-scale creative innovations in methods and constructs.