Perceptions and estimates of error rates in forensic science: A survey of forensic analysts

Every scientific technique features some error, and legal standards for the admissibility of scientific evidence (e.g., Daubert v. Merrill Dow Pharmaceuticals, Inc., 1993; Kumho Tire Co v. Carmichael, 1999) guide trial courts to consider known error rates. However, recent reviews of forensic science conclude that error rates for some common techniques are not well-documented or even established (e.g., NAS, 2009; PCAST, 2016). Furthermore, many forensic analysts have historically denied the presence of error in their field. Therefore, it is important to establish what forensic scientists actually know or believe about errors rates in their disciplines. We surveyed 183 practicing forensic analysts to examine what they think and estimate about error rates in their various disciplines. Results revealed that analysts perceive all types of errors to be rare, with false positive errors even more rare than false negatives. Likewise, analysts typically reported that they prefer to minimize the risk of false positives over false negatives. Most analysts could not specify where error rates for their discipline were documented or published. Their estimates of error in their fields were widely divergent - with some estimates unrealistically low.