Joint recommendations of the project group "Biostatistical DNA Calculations" and the Stain Commission on the Biostatistical Evaluation of Forensic DNA Analytical Findings with Fully Continuous Models (FCM)

Biostatistical evaluation of DNA profiles supports the jurisdiction in the assessment of the evidentiary value of a DNA stain. In order to ensure comparability of such calculations on the basis of established scientific standards, a set of recommendations have already been brought to national consensus in the past. With the introduction of fully continuous models (FCMs) for probabilistic genotyping, which among other things take account of an electropherogram's signal intensities, these recommendations have to be amended. Fully continuous models allow a biostatistical evaluation of complex DNA profiles with presumed allelic drop-in and drop-out events, as well as probability based deductions of individual DNA profiles contributing to a mixture (deconvolution). This publication provides recommendations on the use of FCM-based software and the reporting of fully continuous likelihood ratios (LRfc). It recommends an FCM-based calculation for evaluating the role of an alleged contributor to DNA evidence which is difficult to interpret. Thus it replaces the previous approach of a binary calculation with the exclusion of selected loci, which was previously considered acceptable in exceptional cases. The application of FCM-based software requires comprehensive user training as well as validation and verification according to the software developer's instructions. Furthermore, considerations on LRfc thresholds are described in order to ensure compatibility among probabilistic genotyping results of different origins.