Validation of probabilistic genotyping software for use in forensic DNA casework: Definitions and illustrations

• Definitions of software and model validation are discussed.
• Guidelines for software validation are given.
• Details of the validation of LRmix are discussed.

A number of new computer programs have recently been developed to facilitate the interpretation and statistical weighting of complex DNA profiles in forensic casework. Acceptance of such software in the user community, and subsequent acceptance by the court, relies heavily upon their validation. To date, few guidelines exist that describe the appropriate and sufficient validation of such software used in forensic DNA casework. In this paper, we discuss general principles of software validation and how they could be applied to the interpretation software now being introduced into the forensic community. Importantly, we clarify the relationship between a statistical model and its implementation via software. We use the LRmix program to provide specific examples of how these principles can be implemented.