Abstract
In vast contrast to the multitude of lineup studies that report on the link between decision time, confidence, and identification accuracy, only a few studies looked at these associations for showups, with results varying widely across studies. We therefore set out to test the individual and combined value of decision time and post-decision confidence for diagnosing the accuracy of positive showup decisions using confidence-accuracy characteristic curves and Bayesian analyses. Three-hundred-eighty-four participants viewed a stimulus event and were subsequently presented with two showups which could be target-present or target-absent. As expected, we found a negative decision time-accuracy and a positive post-decision confidence-accuracy correlation for showup selections. Confidence-accuracy characteristic curves demonstrated the expected additive effect of combining both postdictors. Likewise, Bayesian analyses, taking into account all possible target-presence base rate values showed that fast and confident identification decisions were more diagnostic than slow or less confident decisions, with the combination of both being most diagnostic for postdicting accurate and inaccurate decisions. The postdictive value of decision time and post-decision confidence was higher when the prior probability that the suspect is the perpetrator was high compared to when the prior probability that the suspect is the perpetrator was low. The frequent use of showups in practice emphasizes the importance of these findings for court proceedings. Overall, these findings support the idea that courts should have most trust in showup identifications that were made fast and confidently, and least in showup identifications that were made slowly and with low confidence.
Highlights
The identity of a perpetrator is commonly established by means of an identification procedure, for example a police lineup or showup
This paper focuses on positive identification decisions, with one exception: for the Bayesian analyses, hit and false alarm rates were computed, taking into account non-selections as well
Inferential analyses were conducted on log-transformed data due to significant positive skewness and kurtosis in the decision time distribution
Summary
The identity of a perpetrator is commonly established by means of an identification procedure, for example a police lineup or showup. Postdicting positive showup decisions perspective, there is little reason to expect differences between showup and lineups in the confidence-accuracy and decision time-accuracy relationships for positive identifications ( differences can be expected and have been reported for lineup rejections; see [33]) It is surprising, at first sight that the effect sizes in these studies exhibit remarkable heterogeneity, including null [29], small ([26] Experiment 3,[34] Experiment 3,[35] Experiment 1); moderate ([26] Experiment 1,[34] Experiment 2,[36]), and large effects ([35] Experiment 2,[37]). This will be the first study to provide such data for showups
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