Ecological Parameters ≠ Nonlineup Evidence: A Reply to Wells and Luus

The contribution of a lineup identification is in the information it provides about suspect-perpetrator resemblance on top of all other evidence. To assess the diagnostic impact of that contribution, one needs to know the likelihood that an innocent suspect just happens to match the perpetrator in appearance in the way and to the extent inferred from lineup data. Calculating that likelihood calls for statistics about the relative frequency of such a match in the ecology. Therefore, ecological parameters ought to be considered for lineup data just as for other sorts of evidence. Such parameters do not in themselves constitute evidence, but rather serve to estimate diagnosticity of evidence. The index advocated by Wells and Luus (1990) is actually just a measure of lineup reliability. A way to incorporate reliability in the calculation of diagnosticity is presented.