RMNE probability of forensic DNA profiles with allelic drop-out

Abstract

Two methods are commonly used to report on evidence carried by forensic DNA profiles: the “Random Man Not Excluded” (RMNE) approach and the likelihood ratio (LR) approach. Each approach has its advantages and disadvantages. The RMNE approach is much more straightforward to implement, requires less interpretation (which is subject to non-objectivity) and is easier to explain in court. The RNME approach returns a value which is valid, independent of the knowledge of possible contributors. It is often claimed a major advantage of the LR method that drop-out can be assessed probabilistically. We propose new RMNE calculations that likewise account for allelic drop-out in an observed forensic DNA profile. The reported calculations present a non suspect-driven alternative to the poor practice of omitting an inconvenient locus from the standard RMNE calculation when there are loci that require dropped out alleles to allow for a match with the suspect sample. In contrast with the LR approach, the presented RMNE approach does not need error-prone assumptions on the probability P(D) that an allelic drop-out has occurred in the evidence profile. An Excel file with pre-programmed calculations of RMNE probabilities for DNA profiles up to 16 loci and with a maximum of 2 drop-outs is available at: http://www.labfbt.UGent.be/RMNE.php.