The low-template-DNA (stochastic) threshold--its determination relative to risk analysis for national DNA databases

Although the low-template or stochastic threshold is in widespread use and is typically set to 150-200 rfu peak height, there has been no consideration on its determination and meaning. In this paper we propose a definition that is based upon the specific risk of wrongful designation of a heterozygous genotype as a homozygote which could lead to a false exclusion. Conversely, it is possible that a homozygote {a,a} could be designated as {a,F} where 'F' is a 'wild card', and this could lead to increased risk of false inclusion. To determine these risk levels, we analysed an experimental dataset that exhibited extreme drop-out using logistic regression. The derived probabilities are employed in a graphical model to determine the relative risks of wrongful designations that may cause false inclusions and exclusions. The methods described in this paper provide a preliminary solution of risk evaluation for any DNA process that employs a stochastic threshold.