A Review of the ischium-pubis index: accuracy,reliability, and common errors

This article examines the utility of the ischium-pubic index (IPI), a sexing technique that compares the lengths of pubis and ischium. The ratio was adapted by Washburn from a primate index devised by Schultz and was tested by Washburn on documented remains from the Hamann-Todd Human Osteological Collection. The IPI is used by forensic investigators, and indeed, the method is found in standard forensic textbooks and thus appears to be valid to early-stage researchers. However, its reliability has been questioned by physical anthropologists almost from its inception due to the intrinsic subjectivity of locating the base point from which both lengths are taken. In addition, at least one variation of the original technique is found in the literature, which alters the base point profoundly. To explore both the original method and the ramifications of altering the base point, in this article the IPI is calculated from os coxae recovered from the Mary Rose, a 16th-century English warship lost in a documented disaster; the sample is assumed to be from males. Using the original index, 20.4% of individuals (11 of 54) or, viewing the remains as commingled, 15.5% of individual pelves (15 of 97) were misclassified. Results with the base point shifted were disastrous: 95.5% (21 of 22) individuals and 91.4% (32 of 35) pelves were misclassified. Accuracy may be influenced by the technician's expertise; however, when the original methodology is altered, the results become meaningless. This article aims to promote more careful reading of our sources and to suggest that the IPI is not appropriate as a tool for sexing forensic remains.