In this article, the authors present their methodology and analysis of an inter-laboratory trial using probabilistic genotyping software to diagnose the causes of any differences in the likelihood ratios assigned; they discuss the most variable result from the inter-laboratory study; and report the study’s outcomes.
The subject of inter- and intra-laboratory inconsistency was recently raised in a commentary by Itiel Dror. The authors re-visit an inter-laboratory trial, with which some of the authors of this current discussion were associated, to diagnose the causes of any differences in the likelihood ratios (LRs) assigned using probabilistic genotyping software. Some of the variation was due to different decisions that would be made on a case-by-case basis, some due to laboratory policy and would hence differ between laboratories, and the final and smallest part was the run-to-run difference caused by the Monte Carlo aspect of the software used. However, the net variation in LRs was considerable. The authors believe that most laboratories will self-diagnose the cause of their difference from the majority answer and in some, but not all instances will take corrective action. An inter-laboratory exercise consisting of raw data files for relatively straightforward mixtures, such as two mixtures of three or four persons, would allow laboratories to calibrate their procedures and findings. (Published Abstract Provided)