Likelihood ratios for deoxyribonucleic acid (DNA) typing in criminal cases

The likelihood ratio approach for DNA typing in criminal cases is described. It is shown how this approach uses both the sizes and pattern of discrepancies between the crime scene profile of fragment lengths and the suspect profile for quantifying the strength of the evidence. In contrast to the current match-binning approach, it avoids an initial decision about whether the two profiles match. Likelihood ratios for pairs of profiles that meet the published statistical criteria for a match show a wide range of values including some that indicate the evidence is strongly against identity.