Abstract
Eyewitness identification experiments typically involve a single trial: A participant views an event and subsequently makes a lineup decision. As compared to this single-trial paradigm, multiple-trial designs are more efficient, but significantly reduce ecological validity and may affect the strategies that participants use to make lineup decisions. We examined the effects of a number of forensically relevant variables (i.e., memory strength, type of disguise, degree of disguise, and lineup type) on eyewitness accuracy, choosing, and confidence across 12 target-present and 12 target-absent lineup trials (N = 349; 8,376 lineup decisions). The rates of correct rejections and choosing (across both target-present and target-absent lineups) did not vary across the 24 trials, as reflected by main effects or interactions with trial number. Trial number had a significant but trivial quadratic effect on correct identifications (OR = 0.99) and interacted significantly, but again trivially, with disguise type (OR = 1.00). Trial number did not significantly influence participants’ confidence in correct identifications, confidence in correct rejections, or confidence in target-absent selections. Thus, multiple-trial designs appear to have minimal effects on eyewitness accuracy, choosing, and confidence. Researchers should thus consider using multiple-trial designs for conducting eyewitness identification experiments.
Highlights
Eyewitness identification experiments typically involve a single trial: A participant views an event and subsequently makes a lineup decision
We entered all of the fixed effects: memory strength, lineup type, disguise type, degree of disguise, and trial number
In Step 2, we entered the interactions of interest: the interactions of trial number with each of memory strength, lineup type, disguise type, and degree of disguise
Summary
Eyewitness identification experiments typically involve a single trial: A participant views an event and subsequently makes a lineup decision. Eyewitness researchers must decide between maximizing external validity by collecting one data point per participant from a large number of participants and maximizing power, internal validity, and resources by collecting multiple data points per participant. We considered how such repeated-measures designs affect eyewitness accuracy, choosing, and confidence. Only a few studies have explicitly examined the issue of practice (eight studies with target-present lineups; five with target-absent), Shapiro and Penrod concluded that extensive practice (e.g., describing, recognizing, or comparing 90+ faces) is ineffective, but that short (20-minute) training programs may increase facial recognition accuracy This pattern suggests that the Bpractice^ inherent in a multiple-trial design may influence performance on early trials. We expected correct identifications to remain stable across multiple trials or, at most, to slightly increase in early trials and level off in later trials (i.e., a quadratic effect of trial number)
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