Improving eyewitness identification accuracy by screening out those who say they don't know.

Improving eyewitness identification evidence remains a key priority for research. Basic laboratory research has consistently demonstrated that allowing participants to withhold answers about which they are unsure leads to improved accuracy. Surprisingly, this approach has not been the subject of comprehensive investigation in the eyewitness identification literature. In this article, we explored the utility of allowing uncertain witnesses to opt out of an identification decision, by providing an explicit don't know option. Further, we contrasted the rate of use of this explicit option with the frequency that participants spontaneously withheld a decision when asked to respond in their own words. Four hundred and twenty participants witnessed a mock crime video before being presented with a showup of the perpetrator or an innocent suspect. Participants were tested either immediately or after a 3-week delay, with one of the three report options: Participants either made their choice in their own words (spontaneous report), chose between identifying and rejecting the showup (forced-report), or chose between identification, rejection and don't know (free-report). Only 2.2% of witnesses spontaneously used a don't know response, compared to 19.3% who used it when the option was explicit. Compared with the forced-report decisions, free-report decisions were more accurate, more diagnostic of the suspect's guilt or innocence, and came at no cost to the number of correct decisions rendered. These data suggest that utilisation of an explicit don't know option may be of practical value.