ABSTRACT
Chain (MCMC) Methods ...................................... 254 7.4 Statistical Evaluation of Mixtures ......................................................259
7.4.1 The Sampling Formula ............................................................259 7.4.1.1 Shortcut Rules ........................................................ 261 7.4.1.2 When Should a Genotype Be Used in the
Conditioning? .......................................................... 264 7.4.1.3 The General Formula .............................................. 265 7.4.1.4 Mixtures and Relatives ............................................ 268
7.4.2 The Two-Trace Problem and the Factor of 2 ..........................269 7.4.2.1 The Issue of Relevance and the Factor of 2 .......... 269 7.4.2.2 Propositions ............................................................ 270 7.4.2.3 Locus-by-Locus Approach ...................................... 273
7.4.2.5 Unknown Number of Contributors
and Ethnicity .......................................................... 274
The analysis of forensic stains will inevitably lead to mixtures of DNA from different individuals resulting from the mixing of body fluids and secretions. The recognition, resolution, and statistical evaluation of such mixtures are therefore integral and vital parts of forensic casework. The subject is relatively complex and requires experience and judgement. It is often treated as a separate competency by forensic organizations such as ESR and the FSS. Often scientists move to mixture interpretation after experience with simple stains. It is desirable that a formal training and testing program is associated with this transition.
