Meta-analysis of radioulnar contrasts in dermatoglyphic ridge-counts between individual fingers

Radioulnar contrasts (numerically: differences) between ridge counts of individual fingers of the human hand have been identified as promising features in respect to prenatal signalling. In this study, we compared the results of a meta-analysis of intersex differences in radioulnar contrasts between published mean values of dermatoglyphic ridge counts on the fingers of the hand (calculated from the higher RC of each finger) with intersex differences obtained from radioulnar contrasts already calculated at the individual level.Searching the NCBI-PMC, ScienceDirect databases, and archival resources, we found a total of 273 dermatoglyphic studies (after merging duplicates in databases). However, only 11 of those studies were suitable for meta-analysis after application of all selection criteria, including our own four studies. Considering the effort spent in searching for articles, we were able to find very few studies that published statistical parameters of ridge counts by individual finger and that would thus be suitable for studying contrasts between fingers. When statistical parameters have been published for individual fingers, they did not represent the descriptions of all ridge counts from the radial and ulnar sides of the fingers (i.e., 10 values on each hand), but only the ridge count with the higher value is selected for each finger (i.e., 5 values on each hand) at the individual level. The meta-analytically obtained sex dimorphism (contrasts between the mean values of the ridge counts) are virtually indistinguishable from the dimorphism from the contrasts calculated at the individual level (means of the contrasts). However, the step of selecting one (higher) ridge count from each finger blurs the dimorphism and makes interpretation of the sex differences difficult. The results cannot then be compared with those obtained from the complete set of all ridge counts on the fingers.