The “unmotivated bias” of overprecision causes partisan hostility; prior literature has focused on motivated reasoning and social identity theory;overprecision increases hostility directly and indirectly

“Unmotivated bias” and partisan hostility: Empirical evidence. Daniel F. Stone. Journal of Behavioral and Experimental Economics, Volume 79, April 2019, Pages 12-26. https://doi.org/10.1016/j.socec.2018.12.009

Highlights
•    I argue that the “unmotivated bias” of overprecision causes partisan hostility.
•    Prior literature has focused on motivated reasoning and social identity theory.
•    I present evidence that overprecision increases hostility directly and indirectly.
•    The direct effects hold fixed ideology, partisanship, and motivated reasoning.
•    The indirect effects are via increasing strength of partisanship.

Abstract: Extreme partisan animosity has been on the rise in the US and is prevalent around the world. This hostility is typically attributed to social group identity, motivated reasoning, or a combination thereof. In this paper, I empirically examine a novel contributing factor: the “unmotivated” cognitive bias of overprecision (overconfidence in precision of beliefs). Overprecision could cause partisan hostility indirectly via inflated confidence in one’s own ideology, partisan identity, or perceptions of social distance between the parties. Overprecision could also cause this hostility directly by causing excessively strong inferences from observed information that is either skewed against the out-party or simply misunderstood. Using a nationally representative sample, I find consistent support for direct effects of overprecision and mixed support for indirect effects. The point estimates imply a one standard deviation increase in a respondent’s overprecision predicts as much as a 0.71 standard deviation decline in relative out-party favorability.