Filler-siphoning theory does not predict the effect of lineup fairness on the ability to discriminate innocent from guilty suspects: reply to Smith, Wells, Smalarz, and Lampinen (2018)

Smith, Wells, Smalarz, and Lampinen (2018) claim that we (Colloff, Wade, & Strange, 2016) were wrong to conclude that fair lineups enhanced people’s ability to discriminate between innocent and guilty suspects compared to unfair lineups. They argue our results reflect differential-filler-siphoning, not diagnostic-feature-detection. But a manipulation that decreases identifications of innocent suspects more than guilty suspects (i.e., that increases filler-siphoning or conservative responding) does not necessarily increase people’s ability to discriminate between innocent and guilty suspects. Unlike diagnostic-feature-detection, filler-siphoning does not make a prediction about people’s ability to discriminate between innocent and guilty suspects. Moreover, we replicated Colloff et al.’s results in the absence of filler-siphoning (N=2,078). Finally, a model is needed to measure ability to discriminate between innocent and guilty suspects. Smith et al.’s model-based analysis contained several errors. Correcting those errors shows that our model was not faulty, and Smith et al.’s model supports our original conclusions.