The influence of perceived difficulty, availability of marks, and examination time on the conclusions of firearms examiners

Concurrent with studies on the accuracy, repeatability, and reproducibility of decisions based on comparisons of fired bullet and cartridge cases, we also collected the opinions of the participating examiners as to the characteristics of the specimens provided and the difficulty of making comparisons. Examiners rated the ease with which they determined every conclusion (easy, average, hard) and estimated qualitatively the amount of visual information available to them in determining a conclusion (limited, some, extensive). Comparisons deemed hard were perceived generally to have somewhat fewer markings conducive for assessment, while comparisons where the markings were limited produced a larger number of inconclusive determinations. Perceived difficulty increased with wider separation in firing order (within or between three defined segments of 700–850 total firings). The repeatability of these qualitative assessments exceeded 60% and their average reproducibility was ~50%. Examination times did not vary significantly when rendering decisions of identification, elimination, or inconclusive, although bullet identifications appear to have taken slightly longer than those for cartridge cases. Hard comparisons, where the amount of information was limited, were not treated substantially differently from any other types of comparison. No correlation was found between difficulty and number of comparisons attempted. These results tend to contradict assertions by critics that examiners are tempted to declare inconclusive decisions to save time and avoid rendering an elimination or identification conclusion, or that the results are non-representative of casework, or that perceived difficulty affected the degree of examiner participation.