How to measure it
This is the protocol we followed in our most recent papers. You can find detailed information along this guide.
Participants are asked to place both their hands gently but firmly on a scanner to ensure correct scanning. In most cases, we can easily measure the ratio from the scanned pictures. It's important to use a high-resolution scanner allowing for large-scale images in Photoshop.
We measured the distance between the basal crease and the tip of the finger using Photoshop. Figure on the right provides an example and illustrates how finger lengths were measured.
Some additional comments (see the guide to get more precise hints)
a) Double measurement: Repeat the measurement of the 2D:4D (of the scanned pictures) at least twice. The correlation between both measures should be larger than 0.9.
b) Left and right hands: Both hands are equally important. Recent papers on this literature are reporting data from both hands (see for instance, Brañas-Garza et al. 2013)