Clarification of the facts around locus dropping in the FST software developed by the Office of Chief Medical Examiner, New York City

Abstract

FST is a computer program which assigns an LR for DNA profiles created by multiplex STR typing. FST was developed for use by the New York City Office of Chief Medical Examiner (OCME), specifically to interpret DNA profiles processed in their laboratory [1]. The FST source code was publicly released in 2017. FST implements a semi-continuous method of profile interpretation [2], similar to LRmix [3] and Lab Retriever [4, 5]. It was validated to be used for the interpretation of mixed DNA profiles only from two or three contributors. The FST software has a function that ignores a locus, termed locus dropping, if the sum of the probabilities of the alleles observed in the crime scene at the locus exceeds 0.97 ([6] @ pg 172 ln 10). This rule is applied if this sum is reached in any of the four subpopulations used by FST (Asian, African-American, Caucasian, and Hispanic).