Efthymia Nikita

A critical review of the mean measure of divergence and Mahalanobis distances using artificial data and new approaches to the estimation of biodistances employing nonmetric traits

This article reviews the two most common distance measures employed for the calculation of biodistances based on nonmetric traits, the mean measure of divergence (MMD) and the tetrachoric Mahalanobis D(2) distance (TMD). In addition, two new approaches for the estimation of biodistances from nonmetric traits are proposed and assessed. The first (OMD) is based on the direct application of the Mahalanobis distance to ordinally recorded data before their transformation to binary dichotomies. The second (RMD) approximates the covariances of the Mahalanobis distance by the Pearson correlation coefficients calculated in the binary dataset. The application of all four methods to artificial datasets demonstrates that they overall provide a satisfactory estimation of the biodistance among samples especially when the number of statistically non significant distances is very limited. However, the best performance is observed by the OMD, whereas special attention should be paid to the TMD since its values might come out of an ill-conditioned system. The influence of the number of traits, the effect of missing values, as well as the validity of the test statistics used to assess biodistance significance are also examined and discussed.

Evaluating the efficiency of different recording protocols for entheseal changes in regards to expressing activity patterns using archival data and cross-sectional geometric properties.

OBJECTIVES In the past decade there have been extensive discussions on the potential utility of entheseal changes (EC) as activity markers. Nevertheless, no study to date has compared different EC recording protocols with respect to their correlation to activity patterns. MATERIALS AND METHODS This article records changes on fibrocartilaginous entheses of the upper limbs of 90 male skeletons from the documented Athens Collection using the Hawkey and Merbs (Int J Osteoarchaeol 5 (1995) 324-338), Mariotti et al. (Collegium Antropol 28 (2004) 145-159), and Villotte et al. (Am J Phys Anthropol 142 (2010) 224-234) recording schemes in order to determine which one exhibits the highest correlation with activity. Activity is assessed by means of the recorded profession of each individual, as well as employing cross-sectional geometric properties. Generalized Linear Models are used to explore the impact of age, body mass, and activity on EC expression. RESULTS Our results agree with previous studies that age is the primary factor determining EC, whereas body mass is the second most influential factor. In contrast, activity in the form of profession or cross-sectional geometry rarely showed a significant correlation to EC expression and no clear pattern could be discerned irrespective of the recording technique. However, bilateral differences in the impact of age and body mass in EC expression were traced and may relate to activity patterns. CONCLUSIONS The differences found in the bilateral impact of age and body mass highlight the fact that the activity patterns of the individuals under examination must play an underlying role to EC expression, though current recording schemes for EC do not capture this, rendering further work in the direction of developing more elaborate recording standards imperative.