Geographic variability of digital ridge-counts: principal components analysis of male and female world samples

A principal components analysis was made on the means of the ten digital ridge-counts, separately for 195 male populations and 165 female populations, using the variance/covariance matrix. The first three components explain respectively 74%, 12% and 4.6% in the male sample and 77.2%, 11.3% and 4.1% in the female sample. The factor scores of the individual samples were computed and scatter diagrams were plotted for the first two components. They show the existence of a geographic distribution. Ellipses of dispersion of the geographic groups show some similarity between male and female samples, although homogeneity is less than in females and less on the right than on the left hand. The structure of the components shows that the first one corresponds to a factor size, the second contrasts the thumb with fingers 2 and 3, third opposes fingers 2 and 3 to fingers 4 and 5. Data from more recent population studies can easily be referred to the suggested scheme. Their position will define more accurately the differentiation between the geographic groups.