Monday, November 8, 2010

Your lying eyes

Sam Sommers, a social psychologist at Tufts University, has a problem with photo arrays. While preparing to testify as an expert on eyewitness memory, he got a funny feeling about the photo array the complaining witness had viewed.

Mr. Sommers took that photo array, composed of nine photographs, and showed it to 31 people who matched the same basic demographics of the alleged victims. Without providing any details of the crime, he asked each subject to pick the person out of the photo array whom he or she thought committed the crime. He then asked them to make a second choice.

Basic probability tells you that the random sample should pick out the defendant about 11% of the time. Adding a second choice would increase the odds to 2 in 9. The results of the experiment astounded Mr. Sommers.
But in my photo array experiment, 23% of na├»ve respondents picked out the defendant with their first choice, knowing nothing at all about the crime. And a full 45% chose the defendant with either their first or second choice. Statistical analysis confirms that these are significant deviations from chance: for some reason (or reasons), the defendant did stick out like a sore thumb, casting doubt on the usefulness of the actual victims' identifications in the case.
Mr. Sommers decided to run the experiment again to see if the results would be different if he provided details of the crime. For the follow-up he provided the subjects with the same description the victims gave to police.

The second time around the test subjects picked the defendant out of the photo array 29% of the time and 65% of the test subjects picked him out with their first or second choice.

Whether this experiment speaks more to the problems with photo arrays or with eyewitness identification I don't know. It's shocking that the number of people who picked the defendant out of the array, without having any knowledge of the crime or the suspect, was more than twice what blind chance would dictate.

What was it about the photograph? Was the image the same size as the others on the page? Was it the barely visible booking identification number? Did he just have that look?

Perhaps a new method of eyewitness identification needs to be used - such as that The Justice Project proposed in March of last year.

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