Identifying the bad guy

Professor Brewer, Dean of the School of Psychology, has devised a new type of line-up where witnesses are simply asked how confident they are that each line-up member is the culprit, and must respond within a few seconds, rather than trying to point out the perpetrator and having more time to mull it over.

His technique, called “deadline confidence judgements”, has been trialled on more than 900 community members, with the results soon to be published in Psychological Science, one of the world’s most influential psychology journals.

In several experiments conducted over the past three years, Professor Brewer said volunteers watched short films depicting crimes or a mundane event in which one person was prominent.

Half of the participants – some a week later and others within five minutes of the films – were then shown a series of individual pictures from a line-up of 12 people and asked to make a confidence decision about each face within three seconds of it appearing on the computer screen.

They were asked to choose one of 11 options, ranging from “absolutely confident that this is the culprit” to “absolutely certain this is not the culprit”, while the other half of the participants were shown the same faces but given as long as they liked to answer whether each face was or was not the culprit. Sometimes the photos included the culprit and sometimes they did not.

Professor Brewer said a classification “algorithm” produced overall classification accuracy that was 20 to 30 per cent higher than results produced with the conventional line-up.

Moreover, he said the researchers were able to identify particular patterns of confidence judgments across lineup members which showed either a very high or very low likelihood that any individual witness was accurate.

Limiting the time witnesses had to look at suspects yielded better results, Professor Brewer said, because past research showed accurate eyewitness identifications were made significantly faster than inaccurate ones, and that a number of outside factors were removed with a short deadline.

“A weakness of the traditional test lies in the fact that it requires a witness to make a single yes or no decision about a line-up, with plenty of time to reflect on their decision,” Professor Brewer said.

“But the time lapse from the initial viewing to the response often mitigates against witnesses making accurate decisions, as does an array of external factors such as the quality of viewing conditions, attention constraints and social cues that bias the witness towards a positive identification – for example “I saw him for a long time so I should know the answer”.”

Professor Brewer said traditional identification tests often failed because the witness felt “under pressure” to identify a guilty party, however his study showed they were more likely to make accurate identifications if they did not have to be so precise.

“A victim of an assault, for example, has plenty of time to reflect on their decision so they’re more likely to think “if I don’t pick this person, a dangerous man may go free or if I do pick the suspect I’d better be right”, but in a deadline confidence judgement you’re not asking for a yes or no answer.”

Professor Brewer said the rising number of DNA exonerations and the frequent failure of witnesses to identify the culprit mounted a compelling case for a new system of line-ups.

“The fallibility of eyewitness evidence has been consistently highlighted in lab and field studies, and the potency of mistaken identifications has also been dramatically highlighted by the number of DNA exoneration cases,” he said.

Provided by Flinders University