The application of traditional and geometric morphometric analyses for forensic quantification of sexual dimorphism: preliminary investigations in a Western Australian population. Int J Legal Med
A current limitation of forensic practice in Western Australia is a lack of contemporary population-specific standards for biological profiling; this directly relates to the unavailability of documented human skeletal collections. With rapidly advancing technology, however, it is now possible to acquire accurate skeletal measurements from 3D scans contained in medical databases. The purpose of the present study, therefore, is to explore the accuracy of using cranial form to predict sex in adult Australians. Both traditional and geometric morphometric methods are applied to data derived from 3D landmarks acquired in CT-reconstructed crania. The sample comprises multi-detector computed tomography scans of 200 adult individuals; following 3D volume rendering, 46 anatomical landmarks are acquired using OsiriX (version 3.9). Centroid size and shape (first 20 PCs of the Procrustes coordinates) and the inter-landmark (ILD) distances between all possible pairs of landmarks are then calculated. Sex classification effectiveness of the 3D multivariate descriptors of size and shape and selected ILD measurements are assessed and compared; robustness of findings is explored using resampling statistics. Cranial shape and size and the ILD measurements are sexually dimorphic and explain 3.2 to 54.3 % of sample variance; sex classification accuracy is 83.5-88.0 %. Sex estimation using 3D shape appears to have some advantages compared to approaches using size measurements. We have, however, identified a simple and biologically meaningful single non-traditional linear measurement (glabella-zygion) that classifies Western Australian individuals according to sex with a high degree of expected accuracy (87.5-88 %).
Available from: Lesley Kuliukas
- "In contrast, the 3-D GM analysis of the population reported in this Western Australia (WA) study found no such clustering. This WA study is part of a larger project analysing pelvic shape for sex estimation in a forensic context (Franklin et al, 2012a; 2014). "
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ABSTRACT: The objective of this study was to re-evaluate the Caldwell-Moloy (1933) classification of female pelvic shape, which has been traditionally, and still is currently, taught to students of midwifery and medicine. Using modern pelvimetric methodologies and geometric morphometric (GM) analysis techniques, we aim to elucidate whether these classic female pelvic types are an accurate reflection of the real morphometric variation present in the female human pelvis. GM analysis was carried out on sets of pelvic landmarks from scans of women living in a contemporary Western Australian population. Sixty-four anonymous female multi-detector computer tomography (MDCT) scans were used for most of the study and 51 male scans were also examined for comparison. Principle component analysis (PCA) found that there was no obvious clustering into the four distinct types of pelvis (gynaecoid, anthropoid, android and platypelloid) in the Caldwell-Moloy classification, but rather an amorphous, cloudy continuum of shape variation. Until more data is collected to confirm or deny the statistical significance of this shape variation, it is recommended that teachers and authors of midwifery, obstetrics and gynaecological texts be more cautious about continuing to promote the Caldwell-Moloy classification, as our results show no support for the long taught 'four types' of pelvis..
Available from: Thomas Cucchi
- "Predictive accuracy and confidence levels were also compared using Receiver Operator Characteristic Curves (ROC) and the corresponding areas under the curve (AUC) statistic. ROC are computed using posterior probabilities from the LDAs so that the highest curve, with the largest AUC, represents the best predictive model (Franklin et al., 2012; Sanfilippo et al., 2010). "
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ABSTRACT: The ability to document the effects of domestication from archaeological remains of animals and plants is essential for reconstructing the history of one of the most important transitions in human prehistory e the shift from hunting and gathering to farming. In mammals, teeth are well preserved in archaeological remains and are known to be taxonomically informative. In this study, we compare three sets of dental morphometric descriptors in wild and domestic pigs (Sus scrofa) e maximum length, size and shape variables from 2D geometric morphometrics e in order to assess which of the three provides the best ability to correctly distinguish current wild and domestic West Palaearctic pigs. For this purpose, we used predictive linear discriminant analysis with cross-validation taking into account potential bias due to heterogeneous sample sizes and important number of predictors. Classification accuracy of wild and domestic status ranged between 77.3 and 93% depending of the tooth and the descriptor analyzed. However, individual posterior probabilities of correct classification were appreciably smaller when using tooth length and centroid size compared to shape variables. Size appeared to be a poor indicator of wild and domestic status, contrary to shape which in addition provides a high degree of confidence in the wild versus domestic predictions. Our results indicate that geometric morphometrics offers an extremely powerful alternative to more traditional biometric approaches of length and width measurements to capture the elusive morphological changes induced by the domestication process in archaeological remains.
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ABSTRACT: The statistical quantification of error and uncertainty is inherently intertwined with ascertaining the admissibility of forensic evidence in a court of law. In the forensic anthropological discipline, the robustness of any given standard should not only be evaluated according to its stated error but by the accuracy and precision of the raw data (measurements) from which they are derived. In the absence of Australian contemporary documented skeletal collections, medical scans (e.g. multislice computed tomography-MSCT) offer a source of contemporary population-specific data for the formulation of skeletal standards. As the acquisition of morphometric data from clinical MSCT scans is still relatively novel, the purpose of this study is to assess validity of the raw data that is being used to formulate Australian forensic standards. Six human crania were subjected to clinical MSCT at a slice thickness of 0.9 mm. Each cranium and its corresponding volume-rendered three-dimensional MSCT image were measured multiple times. Whether differences between MSCT and dry bone interlandmark measurements are negligible is statistically quantified; intra- and inter-observer measurement error is also assessed. We found that traditional bone measurements are more precise than their MSCT counterparts, although overall differences between the two data acquisition methods are negligible compared to sample variance. Cranial variation accounted on average for more than 20× the variance explained by MSCT vs. bone measurements. Similarly, although differences between operators were sometimes significant compared to intra-operator variance, they were negligible when compared to sample variance, which was on average 12× larger than that due to inter-operator differences.
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