DNA Databases–The Significance of Unique Hits and the Database Controversy

We discuss the database controversy, which deals with the evaluation of the evidential value of a unique match in database search. We conclude that in principle, the case against a suspect is stronger in a database match than in a so-called “cold” case, but contrary to a popular idea, this is not because the likelihood ratio increases when compared to a cold case, but because the posterior odds are higher in the database case.

Keywords: DNA database; unique hit; prior odds; posterior odds; weight of evidence; database controversy; likelihood ratio; hypothesis testing