Facial width (not width relative to height) may be a key to facial sex differences (appears linked in men to other possibly sexually-selected traits)

Caton, Neil R., and Barnaby Dixson. 2022. “Beyond Facial Width-to-height Ratios: Bizygomatic Width Is Highly Sexually Dimorphic When Adjusting for Allometry.” PsyArXiv. February 21. doi:10.31234/osf.io/g5rwm

Abstract: A large literature implicates male facial width-to-height ratio (bizygomatic width divided by facial height) as a secondary sexual trait linked to numerous physical and psychological outcomes. However, this research is based entirely on the premise that bizygomatic width is sexually dimorphic, which recent research has called this into question. Unfortunately, statisticians for the last 125 years have noted that ratio measurements engender spurious correlations and biased effect-size estimates. In the current study, we find that bizygomatic width is highly sexually dimorphic (equivalent d = 1.39). Further, after adjusting for 92 allometric measurements, including multiple facial height and other craniofacial measurements, bizygomatic width exhibited pronounced male-biased sexual dimorphism (equivalent d = 1.01) in a sample of 6,068 men and women born across the globe (Europe, Asia, Oceania, North, Central, and South America). In contrast, fWHR measurements demonstrated a statistical pattern consistent with the age-old argument that ratio measurements engender spurious correlations and biased effect-size estimates. Thus, when avoiding ratios and adjusting for allometry in craniofacial measures, we found strong support for a key premise in the human evolutionary and behavioral sciences that bizygomatic width exhibits male-biased sexual dimorphism.