In conclusion, we believe we made it clear that the true extent of sex differences in human personality has been consistently underestimated. While our current estimate represents a substantial improvement on the existing literature, we urge researchers to replicate this type of analysis with other datasets and different personality measures. An especially critical task will be to compare self-reported personality with observer ratings and other, more objective evaluation methods. Of course, the methodological guidelines presented in this paper can and should be applied to domains of individual differences other than personality, including vocational interests, cognitive abilities, creativity, and so forth. Moreover, the pattern of global sex differences in these domains may help elucidate the meaning and generality of the broad dimension of individual differences known as “masculinity-femininity” [11]. In this way, it will be possible to build a solid foundation for the scientific study of psychological sex differences and their biological and cultural origins.

The researchers used personality measurements from more than 10,000 people, approximately half men and half women. The personality test included 15 personality scales, including such traits as warmth, sensitivity, and perfectionism. When comparing men's and women's overall personality profiles, which take multiple traits into account, very large differences between the sexes became apparent, even though differences look much smaller when each trait is considered separately. However, the study indicates that previous methods to measure such differences have been inadequate, both because they focused on one trait at a time and because they failed to correct for measurement error.

The idea that there are only minor differences between the personality profiles of males and females should be rejected as based on inadequate methodology.

From the paper's conclusion:From the press release 7(1): e29265. doi:10.1371/journal.pone.0029265Marco Del Giudice et al.Sex differences in personality are believed to be comparatively small. However, research in this area has suffered from significant methodological limitations. We advance a set of guidelines for overcoming those limitations: (a) measure personality with a higher resolution than that afforded by the Big Five; (b) estimate sex differences on latent factors; and (c) assess global sex differences with multivariate effect sizes. We then apply these guidelines to a large, representative adult sample, and obtain what is presently the best estimate of global sex differences in personality.Personality measures were obtained from a large US sample (N = 10,261) with the 16PF Questionnaire. Multigroup latent variable modeling was used to estimate sex differences on individual personality dimensions, which were then aggregated to yield a multivariate effect size (Mahalanobis D).Even excluding the factor showing the largest univariate ES, the global effect size was D = 1.71 (24% overlap). These are extremely large differences by psychological standards.