Mean ridge breadth and ridge density tell the same story for ancient fingerprints: A critique of the “Age-Sex Identification Matrix” method of demographic reconstruction

In recent years, the field of archaeological dermatoglyphics has sought to use the ridges of ancient fingerprint impressions to infer demographic information about their creators. Although such a pursuit is inherently challenging, a recent method used in publications (the “Age-Sex Identification Matrix'' approach) relies on flawed assumptions that produce unacceptably inaccurate results. Among other issues, basic mathematics, the literature cited as ostensibly supporting this method, and even the authors’ own published data contradict fundamental assumptions underlying their approach. The two types of fingerprint measurements used in the Age-Sex Identification Matrix approach as proxies for age and sex respectively—mean ridge breadth (distance per ridge) and ridge density (ridges per distance)—are reciprocal values that are not independent. Additionally, in opposition to the methodological thesis of this approach, the previous studies cited in support of this method demonstrate, on the contrary, that both age and sex vary with both mean ridge breadth and ridge density. The published data used in this method also highlight the non-independent nature of the two measures. We caution other researchers to disregard the results of these studies until the data are re-analyzed with a more accurate methodology. Finally, we offer a methodology from the field of Bayesian statistics as an alternative that is able to disentangle the effects of age and sex on fingerprint ridge measurements.