Accounting for multiple effects and the problem of small sample sizes in osteology: a case study focussing on entheseal changes.

Osteoarchaeological studies provide valuable information concerning living conditions and life course changes in past societies. However, many skeletal markers, such as entheseal changes, are multifactorial in aetiology; thus, their interpretation is not straightforward. Generalised linear models (GLMs) are ideal for analysing such phenomena, i.e. those with multiple underlying causative factors, but, to date, their use has been limited. This paper focuses attention on using these models to test hypotheses regarding the aetiology of entheseal changes, widely regarded as indicative of activity patterns, but which are also affected by ageing and body size. To demonstrate the use and limitations of these models, this paper provides an independent test of a previously developed GLM on an identified skeletal sample comprised of skeletons from four British sites ( n = 58) which has a typical sample size for archaeological osteological analysis. In addition to this model, GLMs were developed to include the factor of body size and expand the models to test individual entheses, as well as joint complexes whereby multiple entheses for muscles which act synergistically have been pooled. The results indicate that the original model did not compare well with the frequencies of entheseal changes found in the British assemblage under study. The new models found no clear pattern of influence, although both ageing and body size were important for some entheses. GLMs are appropriate for testing the interaction of biological variables, but future studies need to take into account and test their applicability to archaeological sample sizes. [ABSTRACT FROM AUTHOR]