Comparing analog and digital measurements of the skull : accuracy of measurements based on the Fordisc® data set
Authors:   , Köhler Linda S. 
Published: October 2024

When skeletal remains are found, professionals try to identify the deceased. Specialists, i.e. forensic osteologists, forensic pathologists and anthropologists, are trained in the identification process and answer questions of human specificity, postmortem interval, individual features such as sex, age, height and ethnic origin, as well as signs of injury. Different imaging techniques can aid in the identification process. Further, there is a widely used computer software, Fordisc®, published by Stephen Ousley and Richard Jantz that uses discriminant function analysis for the classification of unknown skeletal remains regarding sex, ancestry and body height. It uses, among others, information from the Forensic Anthropology Data Bank (FDB), which is a centralized database with contemporary skeletal data from identified forensic cases. However, the applicability of Fordisc® to other populations than North America is questionable. In the past, scientists have expressed a desire for a European equivalent of the FDB or an update with a European reference sample. In order to generate a European reference sample, cranial and postcranial measurements must be collected from identified skeletal remains. This can be done either with an analog measuring technique, formed by anthropologists, or, as research has introduced, digitally. Other studies have already investigated whether classical osteometric measurements can be reconstructed and applied from post-mortem computed tomography scans. Digital osteology could be the key to generating a European reference sample more efficiently and without legal issues. In this study, the two different methods were used to take craniometric measurements of 25 skulls. An analog and a digital measuring technique were applied to cranial and mandibular measurements, as used by the Forensic Data Bank Forms by Fordisc®. For the digital measuring technique, the skulls were first scanned with a computed tomography scanner and underwent 3D-reconstruction. The data collected from the two independent analog and digital measurements was statistically analyzed by “Comparison of multiple methods” and visualized with Bland & Altman plots. Of all the 39 measurements, 31 measurements showed a mean difference up to ±2 mm, which is the generally accepted error in an anthropological setting. Most of the measurements, which were not within the accepted error, utilized projection points in the 3D reconstructed image to measure landmarks. The statistical analysis showed significant proportional differences in 13 measurements (p<0,05). Further, the percentage errors were determined: most of the measurements had a median percentage error of < 3%, 17 of the 39 measurements had a median of < 1,5%. This study shows that the following measurements of the Forensic Data Bank could possibly be used to collect digital cranial osseous data with a deviation of ≥- 2 mm to ≤ 2 mm: GOL, XCB, ZYB, BPL, MAB, AUB, UFHT, WFB, UFBR, NLH, NLB, OBB left, OBH right, OBH left, EKB, DKB, FRC, PAC, FOL, FOB, ASB, ZMB, MOW, HMF right, HMF left, TMF left, TMF right, GOG, CDB, WRB right, WRB left. Taking the percentage error into consideration, it is not clear whether all the measurements with an acceptable deviation still fulfill the requirements for digital data collection. Depending on the interpretation of the median percentage error, 24 to 31 accurate measurements were identified, which can possibly be used to generate a necessary reference sample from 3D reconstructed CT images for the Forensic Data Bank. This is something researchers have been asking for, as the quality of the results, when using Fordisc®, is population dependent. Nevertheless, research should continue concerning generally accepted percentage differences or errors in a digital setting, since the meaning of an accepted 2 mm deviation in anthropology, remains unclear.