A now widely studied putative marker for prenatal sex hormones exposure or, more precisely, for the relative exposure to testosterone compared to estrogens while in uterus, is the second-to-fourth digit ratio (2D:4D), that is the ratio between the index (2D) and the ring (4D) fingers.

Digit-ratio app is a tool to obtain anonymous measurements of digit ratios (2D:4D).

Earlier studies that have stood the test of replication have reported that 2D:4D varies by sex and ethnicity but that male 2D:4D tends to be lower than female 2D:4D in all ethnic groups and the effect is strongest in the right hand. These differences emerge prenatally and appear to be stable during the developing years.

While a number of failed replications have been reported, 2D:4D appears to be successfully associated with cognitive abilities, impulsivity, aggression and risk-taking, among other effects on personality and cognition.

The objective of the research project is to collect anonymous measurements from multiple individuals. The measurements and profile data may be sent to a server for research purposes. No image will be sent.