Volume 44, Issue 3 (May 1999)
Bayesian Validation of a Quadruplex STR Profiling System for Identification Purposes
A quadruplex system for determining the genetic profile of an individual at four short tandem repeat (STR) loci has recently been introduced into forensic casework by the Forensic Science Service (FSS), primarily for the purposes of forensic identification. Data have been collected under this system from the three racial groups of most relevance in casework in the UK: Caucasian. Afro-Caribbean and Asian (from the Indian subcontinent). These data are utilized in calculations to quantify the evidential strength of a DNA match between suspect and crime scene sample, say, through the evaluation of a likelihood ratio (LR). Previous papers (1,2) have studied the databases via classical statistical methods. However, we focus on a Bayesian approach (3) to validation of the data for LR evaluation in two main cases: when individuals being compared are either (i) completely unrelated, or (ii) members of the same racial group subpopulation. Empirical studies are conducted to establish the robustness of proposed models and obtain efficient and adequate approximations to the LR calculations. This involves the use of statistical simulation methods to determine the suitability of the product rule and Bayesian inference for coancestry coefficients in the absence of subpopulation data.