E

yewitness misidentiication is the single greatest

cause of wrongful convictions in theUnited States,

having played a role in more than 70% of original

convictions later overturned by newDNAevidence

(www.innocenceproject.org).

This is consistent with a great deal of psychological research

using simulated crimes and lineups. This research shows that

our memories can be surprisingly fallible – we forget impor-

tant details of events, even whole events themselves, and we

remember things that have never happened.What’s worse, we

can make these mistakes even when we seem very conident

that our memories are correct.

Findings like these have cast doubt on the reliability of

eyewitnesses. Even when witnesses appear to remember some-

thing, or someone, strongly and with high conidence, they can

still be wrong.

Our research challenges this widespread view. Rather than

relying on laboratory studies, we were interested in the reliability

of eyewitnesses in actual police lineups and tested two impor-

tant conclusions drawn from laboratory research: that coni-

dence is not a good guide to accuracy, and that sequential lineups

are better than simultaneous lineups.

In a simultaneous lineup, the eyewitness is given all the

photos, usually laid out in a grid, and asked to identify the

person they remember committing the crime. In a sequential

lineup, each photo is presented one-by-one and the eyewitness

is asked to identify whether or not each photo is the culprit.

There is laboratory evidence that accuracy can be greater in

a sequential lineup than in a simultaneous lineup. This is

surprising, because more information is available to the witness

in a simultaneous lineup. While this could aid their decision-

making, it may instead make the decision more confusing.

The data for our study was collected by a member of our

team, William Wells, in collaboration with the Robbery Divi-

sion of the Houston Police Department, where 45 police oi-

cers had presented photo lineups to more than 700 eye witnesses

over a 12-month period. Each lineup included a photo of a

suspect that had been identiied by the police as possibly respon-

sible for the crime, as well as photos of ive innocent “illers”.

Half the lineups were presented simultaneously and the other

half were presented sequentially.

The lineups were conducted fairly – the administering oicer

was unaware which photo was of the suspect. Eyewitnesses who

identiied a photo as the culprit were asked to rate their coni-

dence on a three-point scale: low, medium or high conidence.

Our irst question was whether conidence was a reliable

indicator of accuracy. Unlike laboratory studies, we didn’t

know if the suspect in the photo lineup was innocent or guilty

so we weren’t able to measure accuracy directly. We therefore

approached this problem in two different ways.

First, because the suspect could be the culprit but none of the

innocent illers could be, high accuracy would be relected in a

high level of suspect identiication coupled with a low level of

18 | MAY 2016

How Reliable Is

an Eyewitness?

JOHN DUNN

Eyewitness identification of criminals is notoriously

unreliable, but a new study based on police records

has identified factors that can determine which

witnesses are accurate and which are guessing.

auremar/adobe