No Evidence Against the Greater Male Variability Hypothesis: A Commentary on Harrison et al.’s (2022) Meta-Analysis of Animal Personality

In a recent meta-analysis, Harrison, Noble and Jennions (2022; Biological Reviews, 97, 679-707) set out to test the greater male variability hypothesis with respect to personality in non-human animals. Based on their non-significant results, they concluded that there is no evidence to support the hypothesis, and that biological explanations for greater male variability in human psychological traits should be called into question. Here, we show that these conclusions are unwarranted. Specifically: (a) in mammals, birds, and reptiles/amphibians, the magnitude of the sex differences in variability found in the meta-analysis is entirely in line with previous findings from both humans and non-human animals; (b) the generalized lack of statistical significance does not imply that effect sizes were too small to be considered meaningful, as the study was severely underpowered to detect effect sizes in the plausible range; (c) the results of the meta-analysis can be expected to underestimate the true magnitude of sex differences in the variability of personality, because the behavioral measures employed in most of the original studies contain large amounts of measurement error; and (d) variability effect sizes based on personality scores, latencies, and proportions suffer from lack of statistical validity, adding even more noise to the meta-analysis. In total, Harrison et al.’s study does nothing to disprove the greater male variability hypothesis in mammals, let alone in humans. To the extent that they are valid, the data remain compatible with a wide range of plausible scenarios.