Meta-analysis of digit ratio 2D:4D shows greater sex difference in the right hand.
Level 1 - systematic review of randomized trials
Meta-analysis of cross-sectional anatomical measurement studies (by design analogy, not clinical CEBM).
PubMed 20737609 · doi:10.1002/ajhb.21054
What was done
A random-effects meta-analysis of the second-to-fourth digit length ratio (2D:4D) was performed across 116 samples of expert-measured finger lengths (13,260 females and 11,789 males). The analysis examined sex differences, moderation by age, hand, and measurement technique (specifically soft tissue distortion), and estimated the reliability loss in self-measured digit studies.
What was found
Males showed a moderately lower 2D:4D ratio than females, with substantial heterogeneity across samples that was unrelated to age. The sex difference was significantly moderated by measurement type (larger sex differences occurred when measurement distorted soft tissue) and hand (the right hand showed a larger sex difference than the left). Self-measured 2D:4D from the BBC internet study showed an estimated reliability of only 46% relative to expert measurement, attenuating correlations with variables of interest by about one-third.
Why it matters
It establishes that sex differences in digit ratio are more pronounced in the right hand and warns that self-measured 2D:4D data introduce severe measurement error that attenuates associations.
Limits
The abstract does not provide exact numeric effect sizes (such as Cohen's d or correlation values) or confidence intervals. Substantial heterogeneity was observed across studies and was not explained by age. Prenatal androgen exposure was not directly measured.
Cited by
- supports The sex difference in 2D:4D digit ratio between men and women is more pronounced on the right hand.
- supports The difference in digit ratios (2D:4D) between men and women has an effect size of approximately half a standard deviation.