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Confident witnesses pick the perp

police line up

Confident witnesses are more likely to pick the guilty offender, say researchers (Source: iStockphoto)


But witnesses need to be asked of their confidence straight after they've made their decision to be an effective predictor.

The research is published in the online edition of Law and Human Behaviour.

Psychologist and study author Dr Nathan Weber, of Flinders University in Adelaide, says historically researchers believed that witness confidence and accurate identifications were unrelated.

But, he says, recent research suggests the more confident a witness is with their decision the more accurate they are likely to be.

In the study Weber and his students recruited volunteers from shopping malls and public places around Adelaide.

"The students would then point out a target person to the pseudo-witness before they ducked out of sight," he says.

After the pseudo witness had seen the target, the researchers asked them to identify the person in a photograph and then rate the confidence of their decision.

Weber says the volunteers were asked to measure their confidence on a scale of 0 to 100%.

Some of the volunteers were then asked to pick the same target out of the same line-up three to four weeks later, he says.

They also rated the confidence of their decision.

Confidence equals accuracy

"Almost 90% of the people who said they were 90 to 100% confident with their decision were correct with their identification."

He also says the more confident a witness was with their decision, the less likely they were to pick an innocent person in a line-up.

But Weber says confidence wasn't a good predictor of accuracy if the witness was asked weeks after they made their line-up selection.

He says considering the relationship between confidence and accuracy, police shouldn't rely heavily on the identification of an unconfident witness.

"If someone says their only 30% confident with their decision then you'd want to have a lot of other evidence against someone to prosecute them," says Weber.

Norris Smith of the NSW Police Department says it is standard procedure for police officers to "ascertain the confidence of the witness identification either straight away or a very short time later."

He says all police are taught about the inherent unreliability of eye witness identification.

More evidence needed

Weber agrees, saying it's not a good idea to prosecute someone solely on a witness identification.

His team are now studying how people assess their level of confidence in identification.

"The current thinking is, when you try to work out if you've seen someone before you're matching the face in front of you to an image you have in your mind."

"The more points of match between the image in your mind and the image in front of you, the more confident you'll be," he says.
