How reliable is the charred body scale? An interobserver reliability study on scoring burned remains

The error rates of forensic techniques need to be evaluated. The charred body scale is a method for quantifying the level of decomposition in burned remains. 51 files containing photographs of burned pigs at different stages of decomposition were scored by nine participants. Each pig in the photographs was uniformly burned to a different level (Crow Glassman Scale levels 1 to 3). The Crow Glassman Scale describes five levels of burns that include singing of hair and epidermal blistering (CGS level 1) up to complete cremation of the body reducing it to ash (CGS level 5). The three CGS levels were selected to isolate potential scoring errors that may be caused by different burn levels (not accounted for in the development of the charred body scale). Each of the 51 photograph files was scored by participants using the charred body scale as if it were a unique forensic case at an unknown initial burn level and decomposition stage. Interobserver error, hence reliability, of the scores was tested using individual and average absolute agreement interclass correlations. The charred body scale is reliable for remains burned to a Crow Glassman Scale level 1 but not in higher burn levels. It is suggested that a universal scoring method be developed that accounts for multiple burn levels in a single case.