MSc student Sandra Braun from the University of Pretoria's Physical Anthropology section explains about her research in comparing the digital vs the physical applicability of mandibular non-metric scores.
Can a method that has been used for decades to estimate the sex of an individual based on their bones, be used on a micro-XCT scan of the same bone? As part of a currently ongoing study at the University of Pretoria, we look at whether the analysis of bone is as good as, better, or worse than the analysis of three-dimensional scans of the same bones. For the method in question, researchers look at and score five traits found on the human skull and lower jaw.
Since the usability of scans in anthropology is becoming more and more prominent, it is important to know if this method can be applied to scans and what kind of results can be expected as opposed to the study of real human bones.
Many universities in South Africa have established skeletal collections where the macerated bones of cadavers are stored and used for research and teaching purposes. Skeletal collections are amazing resources, but they are becoming more and more contentious, and very few new bone collections are started. Some of the existing bone collections do not represent modern, current humans and reference values for different methods cannot always be generalised to modern populations. Should the method be applicable to scans, reference values could be taken from patient scans which are done daily at hospitals, after anonymisation.
Sex estimation is essential in forensic anthropology, in the course of victim identification. The University of Pretoria closely collaborates with the South African Police Services and receives human remains for possible identification. Part of the identification process is the estimation of sex, apart from the estimation of ancestry and age at death.
The lower jawbones of 105 individuals were scored by four different observers of different levels of experience. Then the scans of the same 105 individuals were scored by the same observers, independently from one another. One of the observers did the scoring of 25 bones and scans twice to see the consistency of the observation by the same individual (called intraobserver error).
Furthermore, the observers answered a few questions independently on their experience of scoring bone versus scans after they had finished the scoring. The answers were not homologous; while some observers found it more difficult and took more time to score bone, others said they took longer to score the scans only because the file loading in the software took long and that they prefer scoring the bones.
The results show no significant difference between the application of the method to the bone or to the scan; the overall comparison of all four observers for bone was equal to that of the scoring of scans. The intraobserver error, however, turned out to be considerably better for scans than for bone implying that it may be an individual preference to work on bones or rather on scans. This is further supported by the fact that the level of experience did not seem to play a role in the outcome.
We conclude that the same traits can be scored on micro-XCT scans as on physical bone. Digital representations of a bone can be scored sitting at a computer so no physical access to a bone collection is required and there is no need for the researcher to travel to the location of the bone collection. On the other hand, those working in remote conditions might not have access to scanning facilities or the storage space for digital scans.
With the advent of technology, it becomes more and more important to identify the boundaries and overlaps between the digital and physical world.
Sandra Braun
MSc candidate
Forensic Anthropology Research Centre
Department of Anatomy
University of Pretoria