Estimating Sex of the Human Skeleton Based on Metrics of the Sternum
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Estimating the sex of skeletal remains is a critical facet in creating the biological profile of an adult individual. To date, there are different methods utilized on select elements of the skeleton to assess the sex of the individual. Previous research has shown that analyzing the sternum may lead to an accurate estimation of sex based on studies performed on various populations around the globe, such as Indian, European, African, Canadian and the United States (Hunnargi 2009, 2008; Mahakkanukrauh 2008; Selthofer 2006; Torwalt and Hoppa 2005; Gautum 2003; Dahiphale et al. 2002; Mall et al. 1991; McCormick et al. 1985; Stewart and McCormick 1983; Teige 1983; Jit et al. 1980; Dokladal 1978; Rother et al. 1975; Narayan and Varma 1958; Ashley 1956; Dwight 1881, 1889). The motivation of the current study is to determine whether the method is population specific, meaning the data would not prove useful on a recent forensic sample from North America, since the majority of the current research has been performed outside of the United States.
For this study, sternal measurements were collected from the William M. Bass Donated Skeletal Collection located at The University of Tennessee, Knoxville. This collection consists of recent skeletal remains with known age at death, ancestry and sex. The metric definitions provided by Schwartz (2007) and Bass (1987) were followed so that others attempting to replicate this research in the future will be able to reliably measure the sternum. The measurements were taken using a digital sliding caliper, and include length of the manubrium, length of the body, sternebra 1 width and sternebra 3 width. Time was designated at the beginning of the second and third days in order to employ the testretest method. This was used to calculate the intra-observer error rate, and ensure the reliability of these measurements.
In this study, comparisons of the proportion of the length of the manubrium to the length of the sternal body were performed to determine if there are measureable differences between males and females. Based on the work of Dahiphale et al. (2002), it was hypothesized that 1) the body of the sternum in an American population will be greater than twice the length of the manubrium in male samples, and 2) in female samples, the length of the manubrium will be greater than half the length of the sternal body. This is referred to as Hyrtl’s Law (Dahipahale et al. 2002; Hyrtl 1878). In addition, comparisons of these measurements between individuals identified as American Black and American White were analyzed to determine whether this method could be used on both population groups.
Material for the present study consisted of 410 human sterna: 285 male (256 American White/29 American Black) and 125 female (120 American White/5 American Black). The data were entered into Statistical Analysis Software (SAS) computer program version 9.1.3. A discriminate function analysis (DFA), using all variables, produced an overall cross-validation classification rate of 84.12% for sex estimation. The cross-validation classification rate for males and females was 80.00% and 88.24%, respectively. The author will discuss the applicability of utilizing the sternum as a method of sex estimation and propose specialists in the field adopt it as a supplementary method for use in human identification.