Jordan Peterson on psychology: what the evidence says · JRE #1769

What the evidence says 01 / RECORD

Peterson invokes a specific 10% figure to describe overlap between male and female personality distributions, then immediately hedges that it could be "5% and 40 or something," indicating the number is illustrative rather than cited from a specific study. Research does support the general premise that male and female personality distributions differ more than earlier research suggested when multiple traits are combined into a composite measure: Del Giudice et al. (2012, PLoS ONE), using a large representative sample (N=10,261) and the 16PF questionnaire, calculated a multivariate effect size (Mahalanobis D = 2.71) corresponding to an overlap of only about 10% between the aggregate male and female personality distributions, a figure that closely echoes Peterson's number. However, that study measures overlap between multivariate composite profiles across many trait dimensions, not the specific claim Peterson makes, that a given percentage of individual men or women score as far into the "opposite" range as the average member of that sex. On single traits, sex differences in personality are typically small to moderate (Cohen's d around 0.1-0.5), and the psychological literature is genuinely split between researchers emphasizing broad similarity (the "gender similarities hypothesis") and researchers like Del Giudice emphasizing that composite, multivariate measures reveal much larger differences. No study was found that directly measures the precise quantity Peterson describes, so his 10% figure should be treated as an approximate, illustrative estimate loosely consistent with, but not directly validated by, the personality-overlap research literature.