Is digit ratio (2D: 4D) related to systemizing and empathizing? Evidence from direct finger measurements reported in the BBC internet survey

The ratio of 2nd to 4th digit length (2D:4D), the systemizing quotient (SQ) and the empathizing quotient (EQ) are putative correlates of prenatal testosterone. However, the evidence that 2D:4D is related to SQ or EQ is mixed. Voracek and Dressler (2006) used indirect finger measurements and found no significant associations with 2D:4D and SQ or EQ, whereas von Horn, Bäckman, Davidsson, and Hansen (2010) reported significant correlations between 2D:4D and a composite measure of SQ and EQ using direct finger measurements. Here we report associations of 2D:4D, SQ and EQ in participants from a large internet survey in which direct measurements of fingers were collected. We found (i) significant negative correlations of SQ with 2D:4D, this being stronger for right hand 2D:4D and independent of sex, age, height, ethnicity, sexual orientation, and education, (ii) no significant correlation of EQ and 2D:4D. We further examined mean 2D:4D’s and found suggestions of a distortional effect of indirect finger measurement in the Voracek and Dressler (2006) study. Our results partly replicate those of von Horn et al. (2010) and emphasize the use of direct finger measurements when studying associations between 2D:4D and target traits with small effect size.