PhD Dissertations: Marina Elliott, 2015

Estimating Body Mass In Biological Anthropology: An Evaluation Using Three-Dimensional Computed Tomography

 

Abstract

Body mass estimations are essential to biological anthropology research. The primary source for this information is skeletal morphology and several sets of predictive equations have been developed for cranial and postcranial material. These equations are widely used, but a number of factors suggest that they may not be as reliable as they are generally assumed to be. In particular, reference samples are often small and regressions frequently employ indirect measurements, unassociated material and mean data. In addition, tests of the equations have rarely involved external validation on samples of known mass.

This research addressed these issues by investigating three aspects of body mass estimation using a large documented sample of modern humans with associated skeletal measurements reconstructed from whole-body computed tomography scans. The first study assessed three sets of commonly employed cranial equations for accuracy and compared the results. The second study assessed existing postcranial equations and compared the results to previous evaluations that used smaller test samples, indirectly measured variables and unassociated masses. Several assumptions relating to the way the equations were expected to perform were also explicitly tested. The final study developed new regression equations for estimating mass from cranial and postcranial variables using the same individuals. This permitted the direct comparison of the two approaches and provided insight into the effect of variable choice, statistical method and evaluation criteria on estimation competence.

The results suggest that body mass estimates must be used more cautiously than is the current practice in biological anthropology. Overall, cranial variables did not estimate mass accurately and specific features that had been described as reliable estimators, did not perform well. Postcranial variables estimated mass more accurately, but not consistently. The equations also did not always perform in accordance with previous assumptions. Deriving new equations using a known reference sample improved estimation competence compared to previous studies, but accuracy rates remained low. Assumptions about the best criteria to use for evaluating predictive competence were not supported. Further research may explain these discrepancies, but body mass estimates must be made judiciously and interpreted as approximations at best.