X-ray of a proximal femur. Image courtesy of Ann Ross.Forensic examiners generally rely on a “mixed bag” of standards when determining the certainty of a post-mortem identification, according to North Carolina State University professor Ann Ross.

Her new study, published last week in the American Journal of Forensic Medicine and Pathology, set out to determine the probability of positively identifying human remains through X-ray examinations of the three most common locations: the side of the skull, the spine and the upper leg.

“We've created a set of standards that will allow for a consistent approach to identification—that can be replicated—and that allows experts to determine probabilities for an identification,” Ross, the lead author, said in a statement provide by the university. “For example, you could say with 85 percent certainty that a body is a specific individual.”

Researchers also created a “decision tree” that will give forensic experts statistical probabilities of positive IDs that can help with determining uncertainty calculations.

The study included hundreds of X-ray images from dozens of participants of both ante-mortem and postmortem bone structures for comparison. Twenty individuals were X-rayed for lateral craniofacial comparison, 50 individuals for the vertebral column, and 23 for the proximal femur, according to researchers.

Based on “concordant areas”—the areas that positively match in both the ante-mortem and postmortem X-rays—the different locations came back with different rates for positive identification. The most definitive locations were the skull and spine, 97 and 98 percent respectively, with misclassification rates of 10 and 7 percent. The lower back performed much worse: as low as 40 percent misclassification rate, according to the study.

“Lumbar X-rays can be used to support information from other skeletal locations,” Ross said in the statement, “but we think they are too unreliable to be used as the primary means of identification.”

The research, called “Establishing Standards for Side-by-Side Radiographic Comparisons,” was funded by the National Institutes of Justice.