Mis)use of Scientific Measurements in Forensic Science

Forensic science error rate studies have not given sufficient attention or weight to inconclusive evidence and inconclusive decisions. Inconclusive decisions can be correct decisions, but they can also be incorrect decisions. This can occur when inconclusive evidence is determined as an identification or exclusion, or conversely, when same- or different-source evidence is incorrectly determined as inconclusive. We present four common flaws in error rate studies: 1. Not including test items which are more prone to error; 2. Excluding inconclusive decisions from error rate calculations; 3. Counting inconclusive decisions as correct in error rate calculations; and 4. Examiners resorting to more inconclusive decisions during error rate studies than they do in casework. These flaws seriously undermine the credibility and accuracy of error rates reported in studies. To remedy these shortcomings, we present the problems and show the way forward by providing a corrected experimental design that quantifies error rates more accurately.