DNA profiling: evaluation of the evidentiary value

The evaluation of the evidentiary value of scientific evidence is the assessment of the strength of the link between a finding and a person. It is usually a statistical assessment but its presentation is full of pitfalls. The evaluation of scientific evidence must be based on a established methodology to both evaluate, expose and interpret the evidence. It is best based on a logical framework, e.g. the Bayesian theorem, and on likelihood ratios. The information of the scientist is usually a numerical one, e.g. the probability of observing two matching profiles. Assessments of simple stains as well as of stain mixtures with contributors of different ethnic origin and/or with related contributors or reference persons and even artifacts can be quantified and expressed by likelihood ratio(s). Thereby, scientific evidence can be integrated by juries into the continuous process of evaluating prior odds and changing them into posterior odds by new information in the case.