Accuracy of the Phenice (1969) and Klales (2012) sex estimation methods in a Chilean population

A violent military dictatorship ruled Chile from 1973 until 1990. As a result, more than 3 million individuals were tortured, killed, or missing. The search for and identification of the victims’ remains is a crucial part of the historical and judicial procedures for reparation in human rights cases in Chile. The Chilean Medico-Legal Service is the public entity in charge of analysing skeletal remains associated with those cases. The standards for biological assessment currently used by the service are usually performed by applying methods developed for North American or European reference populations. One of the methods currently used by this institution to estimate sex is the Phenice method (1969), based on the observation of three traits in the coxae: ventral arc, subpubic concavity, and medial aspect of the ischiopubic ramus. The stated accuracy of Phenice is 95% using multiple criteria. Klales (2012) subsequently developed an equation for estimating sex using the same features but using 1-5 scoring system. The stated accuracy is 86.2% using all three traits (74.4% males; 98% females). However, current research has demonstrated that the accuracy of these methods can be substantially reduced when applied to individuals geographically distant from the original reference groups. Therefore, considering the importance of validating anthropological standards, this study aimed to test the classification accuracy of these methods in a documented contemporary Chilean sample. The sample comprised 265 coxae (196 males; 69 females) of adult Chilean individuals of documented sex from the Sub-actual General Cemetery of Santiago skeletal collection. Visual assessments and scoring of the pelvic traits were performed following the descriptions and illustrations made by Phenice (1969) and Klales (2012), respectively. The percentage of correct classification and sex bias were calculated by comparing the documented sex with the results obtained from the two sex estimation methods following Phenice (1969) and Klales (2012). The Phenice method’s overall accuracy for the Chilean sample was 96.98% (98.98% males; 91.30% females), with a sex bias of 7.68%. Klales’ method showed an overall accuracy of 87.2% (83.2% males, 98.6% females), with a sex bias of -15.4. Although these results represent appropriate accuracy, they revealed a sex bias over 5% that could lead to errors in the estimations, favouring one sex relative to the other. Thus, forensic practitioners working
with Chilean skeletal remains should be warned about using these methods for future sex assessments.