Effect of Age on Nonmetric Cranial Traits for Sex Estimation in Adults

Buikstra and Ubelaker (1994) standardized a set of commonly used nonmetric cranial traits, including the nuchal crest, mastoid process, supraorbital margin, glabella, and mental eminence, for sex estimation of unknown skeletal remains. Walker (2008) presented cranial trait scoring data from several populations and developed logistic regression equations to estimate sex from cranial trait scores, which has become a popular method in forensic anthropology. The aim of the present research is to evaluate the effect of age on the scoring of the five cranial traits examined by Walker. A large, uniformly age-distributed sample of adults (20–92 years; n = 272) of European-American and African-American ancestry from the Hamann-Todd Osteological Collection was examined by two observers. A third observer contributed data also from the Hamann-Todd Collection (20–85 years; n = 333). Ordinal logistic regression and pseudo-R2 tests revealed some significant effects of age on the mastoid process, supraorbital margin, glabella, and mental eminence, depending on the observer and data set. However, the magnitude of these effects is negligible, with age accounting for a maximum of only 5% of the variance in trait scores. Despite assertions in several commonly used texts that female skulls tend to become more masculinized with age, the results of the present research indicate that age does not play a significant role in the scoring of the five cranial traits evaluated by Walker (2008). KEYWORDS: forensic anthropology, age effect, Walker traits, skull, sex estimation