Presence bias and the insensitivity to the diagnosticity of nonidentifications

There is both theoretical ground and empirical evidence to suggest that nonidentifications in police line-ups are diagnostic of the suspect's innocence. However, it is frequently assumed that both laypeople and legal decision makers fail to appreciate this diagnosticity. It is hypothesized that this underestimation is fuelled by a general reluctance to accept null findings. To test this idea, participants judged the importance of nonidentifications and foil identifications. As predicted, foil identifications were considered to have more diagnostic power than nonidentifications (Study 1). In Studies 2 and 3, the hypothesis was tested that nonidentifications intuitively generate more uncertainty than suspect and foil identifications. This hypothesis was confirmed in that participants were able to conjure up more alternative explanations for nonidentifications compared to suspect and foil identifications. Findings are discussed in the light of what can be called presence bias.

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