Lack of correlation between 2D:4D ratio and assertiveness in college age women

Lack of association between digit ratio (2D:4D) and assertiveness: replication in a large sample

Findings regarding within-sex associations of digit ratio (2D:4D), a putative pointer to long-lasting effects of prenatal androgen action, and sexually differentiated personality traits have generally been inconsistent or unreplicable, suggesting that effects in this domain, if any, are likely small. In contrast to evidence from Wilson's important 1983 study, a forerunner of modern 2D:4D research, two recent studies in 2005 and 2008 by Freeman, et al. and Hampson, et al. showed assertiveness, a presumably male-typed personality trait, was not associated with 2D:4D; however, these studies were clearly statistically underpowered. Hence this study examined this question anew, based on a large sample of 491 men and 627 women. Assertiveness was only modestly sexually differentiated, favoring men, and a positive correlate of age and education and a negative correlate of weight and Body Mass Index among women, but not men. Replicating the two prior studies, 2D:4D was throughout unrelated to assertiveness scores. This null finding was preserved with controls for correlates of assertiveness, also in nonparametric analysis and with tests for curvilinear relations. Discussed are implications of this specific null finding, now replicated in a large sample, for studies of 2D:4D and personality in general and novel research approaches to proceed in this field.

Scientometric analysis and bibliography of digit ratio (2D:4D) research, 1998-2008

A scientometric analysis of modern research on the second-to-fourth digit ratio (2D:4D), a widely studied putative marker for prenatal androgen action, is presented. In early 2009, this literature totalled more than 300 publications and, since its initiation in 1998, has grown at a rate slightly faster than linear. Key findings included evidence of publication bias and citation bias, incomplete coverage and outdatedness of existing reviews, and a dearth of meta-analyses in this field. 2D:4D research clusters noticeably in terms of researchers, institutions, countries, and journals involved. Although 2D:4D is an anthropometric trait, most of the research has been conducted at psychology departments, not anthropology departments. However, 2D:4D research has not been predominantly published in core and specialized journals of psychology, but rather in more broadly scoped journals of the behavioral sciences, biomedical social sciences, and neurosciences. Total citation numbers of 2D:4D papers for the most part were not larger than their citation counts within 2D:4D research, indicating that until now, only a few 2D:4D studies have attained broader interest outside this specific field. Comparative citation analyses show that 2D:4D research presently is commensurate in size and importance to evolutionary psychological jealousy research, but has grown faster than the latter field. In contrast, it is much smaller and has spread more slowly than research about the Implicit Association Test Fifteen conjectures about anticipated trends in 2D:4D research are outlined, appendixed by a first-time bibliography of the entirety of the published 2D:4D literature.

2d:4d, sex steroid hormones and human psychological sex differences

Studies on 2d:4d, the ratio between the second and the fourth digit, as a possible indicator of prenatal androgen exposure, have failed to produce consistent results. This paper analyzes the relation between 2d:4d, sex steroids and well-documented sex differences in characteristics such as depression, dominance, and aggressive (ART) and non-aggressive adolescent risk-taking (NART) in a comparatively large sample of adolescent boys (N=301, mean age: 14.4 years) and girls (N=298, mean age: 14.3 years). Boys had on average a lower 2d:4d than girls (F=42.15; p<0.001). With respect to boys, controlling for age and pubertal development (PD), a small but marginally significant positive association was found between 2d:4d and total testosterone (TT) (r=0.11; p<0.05). In girls a significant association was found between 2d:4d and SHBG (r=0.18; p<0.01). However, relationships between 2d:4d and hormones depended on the phase of the menstrual cycle, with 2d:4d being negatively associated with FT (B=-0.013; p<0.05) once a positive association between 2d:4d and FT for girls in the mid-cycle group (B=0.019; p<0.01) is taken into account. With respect to sex differences in characteristics, we found evidence of a relationship between 2d:4d and depression in boys (r=-0.14; p<0.05) but not between 2d:4d and dominance, ART or NART. No relationships were found between 2d:4d and any of these variables in girls.

On the relation between 2D:4D and sex-dimorphic personality traits

Several personality traits, including aggressiveness and sensation seeking, have been hypothesized to be influenced by prenatal androgen exposure, though evidence for this proposition is limited. We investigated whether individual differences in aggressiveness, sensation seeking, and several prosocial personality traits can be predicted from differences in the 2D:4D digit ratio, a putative marker of prenatal androgen activity. A total of 164 undergraduates (87 men, 77 women) completed self-report measures of physical and verbal aggression, as well as a standardized measure of sensation seeking, and five scales to assess empathy, nurturance, expressivity/femininity, instrumentality/masculinity, and assertiveness. Two sex-dimorphic tests of spatial ability also were included. Men had a lower 2D:4D ratio than women, confirming the typical sex difference in digit proportions. Significant sex differences were observed on 10 of the 11 personality scales purported to show sex differences and on both tests of spatial ability. The 2D:4D ratio was a significant predictor of scores on three of the four aggression subscales, total aggression, thrill and adventure seeking, and total sensation-seeking, in the sample as a whole and in women. In men, correlations with 2D:4D were significant only for total sensation-seeking and verbal aggression. In both sexes, lower 2D:4D ratios were associated with increased aggressiveness and sensation seeking. For the spatial tests, there was no evidence of any association with 2D:4D in either men or women. The 2D:4D digit ratio may be a valid, though weak, predictor of selective sex-dependent traits that are sensitive to testosterone.