Eastern Baltic region vs. Western Europe: modelling age related changes in the pubic symphysis and the auricular...

Objectives. The present study addresses the following two main questions: a) Is the pattern of skeletal ageing observed in well-known western European reference collections applicable to modern eastern Baltic populations, or are population-specific standards needed? b) What are the consequences for estimating the age-at-death distribution in the target population when differences in the estimates from reference data are not taken into account? Materials and methods. The dataset consists of a modern Lithuanian osteological reference collection, which is the only collection of this type in the eastern Baltic countries (n = 381); and two major western European reference collections, Coimbra (n = 264) and Spitalfields (n = 239). The age-related changes were evaluated using the scoring systems of Suchey-Brooks (Brooks & Suchey 1990) and Lovejoy et al. (1985), and were modelled via regression models for multinomial responses. A controlled experiment based on simulations and the Rostock Manifesto estimation protocol (Wood et al. 2002) was then carried out to assess the effect of using estimates from different reference samples and different regression models on estimates of the age-at-death distribution in the hypothetical target population. Results. The following key results were obtained in this study. a) The morphological alterations in the pubic symphysis were much faster among women than among men at comparable ages in all three reference samples. In contrast, we found no strong evidence in any of the reference samples that sex is an important factor to explain rate of changes in the auricular surface. b) The rate of ageing in the pubic symphysis seems to be similar across the three reference samples, but there is little evidence of a similar pattern in the auricular surface. That is, the estimated rate of age-related changes in the auricular surface was much faster in the LORC and the Coimbra samples than in the Spitalfields sample. c) The results of simulations showed that the differences in the estimates from the reference data result in noticeably different age-at-death distributions in the target population. Thus, a degree bias may be expected if estimates from the western European reference data are used to collect information on ages at death in the eastern Baltic region based on the changes in the auricular surface. d) Moreover, the bias is expected to be more pronounced if the fitted regression model improperly describes the reference data. Conclusions. Differences in the timing of age-related changes in skeletal traits are to be expected among European reference samples, and cannot be ignored when seeking to reliably estimate an age-at-death distribution in the target population. This form of bias should be taken into consideration in further studies of skeletal samples from the eastern Baltic region.