Between a ROC and a hard place: The criminological implications of measures pertaining to eyewitness identification procedures.

Mr Dominic Jordan1, Dr Adrian  Scott2, Professor Donald Thomson3, Associate Professor Pamela Henry1

1Edith Cowan University, Joondalup , Australia,

2Goldsmiths, University of London , New Cross, United Kingdom,

3Deakin University, Geelong, Australia

Conclusions regarding the applied suitability of different lineup procedures (simultaneous and sequential) have been informed by analytical approaches which convert raw data (conditional probabilities; CP) into singular scores such as the diagnosticity ratio (DR) or Reciever Operating Characteristic (ROC) analysis. Although there are inherent benefits to using such measures, consideration of CP may be important when drawing conclusions regarding the applied suitability of different lineup procedures. Three analytical approaches (ROC, DR and CP) were applied to a single data set to determine 1) whether patterns of results were consistent and 2) to assess the practical value of each approach. This study adopted an experimental 2 (Simultaneous v Sequential) x 2 (Target present: TP v Target absent: TA) between-participants design. Participants (N=1259) made identifications and confidence judgements from two eight-person photographic lineups (TP and TA). Participant decisions were analysed using ROC, DR and CP. For lineup one, all three measures indicated that the simultaneous lineup significantly outperformed the sequential lineup. For lineup two some disparity in the findings was observed. ROC and DR produced evidence to suggest that there was no-significant difference between the accuracy of decisions across lineup procedure type. Analysis of CP suggested that the simultaneous lineup produced significantly more accurate decisions in both TP and TA conditions than the sequential lineup. The data indicates that ROC and DR may obscure important information regarding lineups applied suitability. CP may provide practitioners with more transparent information regarding the suitability of lineup procedures to be used in an applied setting.


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