Exploring cranial macromorphoscopic variation and classification accuracy in a South African sample.

To date South African forensic anthropologists are only able to successfully apply a metric approach to estimate population affinity when constructing a biological profile from skeletal remains. While a non-metric, or macromorphoscopic approach exists, limited research has been conducted to explore its use in a South African population. This study aimed to explore 17 cranial macromorphoscopic traits to develop improved methodology for the estimation of population affinity among black, white and coloured South Africans and for the method to be compliant with standards of best practice. The trait frequency distributions revealed substantial group variation and overlap, and not a single trait can be considered characteristic of any one population group. Kruskal-Wallis and Dunn's tests demonstrated significant population differences for 13 of the 17 traits. Random forest modelling was used to develop classification models to assess the reliability and accuracy of the traits in identifying population affinity. Overall, the model including all traits obtained a classification accuracy of 79% when assessing population affinity, which is comparable to current craniometric methods. The variable importance indicates that all the traits contributed some information to the model, with the inferior nasal margin, nasal bone contour, and nasal aperture shape ranked the most useful for classification. Thus, this study validates the use of macromorphoscopic traits in a South African sample, and the population-specific data from this study can potentially be incorporated into forensic casework and skeletal analyses in South Africa to improve population affinity estimates.

Veldt fires in South Africa: Implications on osteometry and the biological profile.

Standard operating procedures for forensic anthropological analyses dictate that thermally altered remains should not be measured, hindering the creation of a biological profile. Few studies have addressed estimating biological parameters from burned remains, with the greatest focus of this research area being on cremated remains. However, veldt fires are more common than cremation in the South African forensic context. The aim of this study was to explore the degree of structural changes observed in domestic pig (Sus scrofa) bones associated with thermal destruction and the potential impact on the estimation of a biological profile using standard osteometric methods. A total of 96 pig femora were divided equally into two categories: fresh and dry. Within each category, equal samples were exposed to different durations of burning, namely, 5, 10, and 20 min. Ten standard femoral anthropological measurements were collected before and after burning. Technical error of measurement and Wilcoxon signed-rank tests were used to assess changes in the femoral dimensions before and after burning. Most measurements were significantly different after burning, with the fresh bones decreasing in size by up to 7.8% and the dry bones decreasing in size by up to 4.0%. The magnitude of post-burning measurement changes for both burn conditions was similar to, or smaller than has previously been reported for observer measurement errors of commonly used variables investigated for standard osteometric studies. Veldt fires are less intense than cremation, thus causing less shrinkage.

Standardization and quality assurance in skeletal landmark placement and osteometry.

Studies revising methodology are essential to the development and standardization of the field of anthropology, especially as the ultimate goal is improved forensic analyses. A series of revisions were made to the Standards for Data Collection Procedures reference manual. This includes changes made to the definitions of several standard measurements ranging from modified landmark placement to variation in the proper orientation of the caliper. The aim of this paper was to compare measurements collected using the different sets of definitions to determine if the measurements would differ significantly. Fifteen measurements were collected from 30 crania and postcrania, first using the original definitions, and then using the modified definitions and/or landmarks. The measurement differences for the 2 sets of definitions were assessed using technical error of measurement and a Kruskal-Wallis test. Results indicate that 8 of the 15 measurements differed significantly when the modified definitions were employed. Therefore, data collected using the different sets of definitions should not be used interchangeably. Forensic practitioners and laboratories making use of the updated reference manual must take into consideration how the current results might influence their standard operating procedures. Furthermore, all databases that currently make use of the original measurements, such as the South African-specific databases used in Fordisc, must be updated to include the modified measurements to stay on par with international data collection standards.

Postcraniometric sex and ancestry estimation in South Africa: a validation study.

With the acceptance of the Daubert criteria as the standards for best practice in forensic anthropological research, more emphasis is being placed on the validation of published methods. Methods, both traditional and novel, need to be validated, adjusted, and refined for optimal performance within forensic anthropological analyses. Recently, a custom postcranial database of modern South Africans was created for use in Fordisc 3.1. Classification accuracies of up to 85% for ancestry estimation and 98% for sex estimation were achieved using a multivariate approach. To measure the external validity and report more realistic performance statistics, an independent sample was tested. The postcrania from 180 black, white, and colored South Africans were measured and classified using the custom postcranial database. A decrease in accuracy was observed for both ancestry estimation (79%) and sex estimation (95%) of the validation sample. When incorporating both sex and ancestry simultaneously, the method achieved 70% accuracy, and 79% accuracy when sex-specific ancestry analyses were run. Classification matrices revealed that postcrania were more likely to misclassify as a result of ancestry rather than sex. While both sex and ancestry influence the size of an individual, sex differences are more marked in the postcranial skeleton and are therefore easier to identify. The external validity of the postcranial database was verified and therefore shown to be a useful tool for forensic casework in South Africa. While the classification rates were slightly lower than the original method, this is expected when a method is generalized.

Population differences in the postcrania of modern South Africans and the implications for ancestry estimation.

The cranium is widely recognized as the most important skeletal element to use when evaluating population differences and estimating ancestry. However, the cranium is not always intact or available for analysis, which emphasizes the need for postcranial alternatives. The purpose of this study was to quantify postcraniometric differences among South Africans that can be used to estimate ancestry. Thirty-nine standard measurements from 11 postcranial bones were collected from 360 modern black, white and coloured South Africans; the sex and ancestry distribution were equal. Group differences were explored with analysis of variance (ANOVA) and Tukey's honestly significant difference (HSD) test. Linear and flexible discriminant analysis (LDA and FDA, respectively) were conducted with bone models as well as numerous multivariate subsets to identify the model and method that yielded the highest correct classifications. Leave-one-out (LDA) and k-fold (k=10; FDA) cross-validation with equal priors were used for all models. ANOVA and Tukey's HSD results reveal statistically significant differences between at least two of the three groups for the majority of the variables, with varying degrees of group overlap. Bone models, which consisted of all measurements per bone, resulted in low accuracies that ranged from 46% to 63% (LDA) and 41% to 66% (FDA). In contrast, the multivariate subsets, which consisted of different variable combinations from all elements, achieved accuracies as high as 85% (LDA) and 87% (FDA). Thus, when using a multivariate approach, the postcranial skeleton can distinguish among three modern South African groups with high accuracy.

Evaluating the Accuracy of Cranial Indices in Ancestry Estimation Among South African Groups.

Historically, population differences were quantified using cranial indices. Even though the application of indices is associated with numerous statistical and methodological problems, the use of cranial indices to estimate ancestry persists as demonstrated by its inclusion in several recent papers and conference presentations. The purpose of this study was to classify 207 South African crania and compare the results of five standard cranial indices to linear discriminant analysis (LDA). New sectioning points were created to contend with low classification accuracies (40-79%) and possible secular trends. Although the accuracies of the new sectioning points increased (66-87%), the accuracies associated with the stepwise LDA were higher (84%) and could classify the crania into one of the three South African groups. The results of the study demonstrate that indices cannot compete with multivariate techniques and should not be used in forensic anthropological analyses for ancestry estimation.