Eyewitness testimony is one of the oldest forms of evidence in criminal court cases, and probably the most persuasive. But human memory is notoriously faulty, and our nation's dependence on—and trust in—eyewitnesses has been the largest driver of wrongful convictions in the United States. Here's a new slice of hope though: A new study, published today in Proceedings of the National Academy of Sciences, shows that eyewitness accounts can still be useful—as long as those witnesses are confident.
In a field study of 348 eyewitness accounts of actual crimes in Houston, Texas, a team of researchers examined whether the type of line-up police officers used influenced witness accuracy. The team assigned investigators who did not know the identify of the suspect to issue line-ups either simultaneously—when witnesses are presented with a potential suspect and five "fillers," or people known to be innocent, at the same time; or sequentially—in other words, each person in the line-up is presented to the witness one at a time. The researchers also measured witnesses' confidence levels, to find out if that might be linked to the accuracy of their identifications.
Indeed, they found confidence was a strong predictor of accuracy, and that simultaneous line-ups were slightly better than sequential ones—a surprising finding that goes against the tide of current consensus around which line-up format garners the most accurate results. After a slew of mock crime studies in recent years favored sequential line-ups over the simultaneous variety, upwards of 30 percent of law enforcement agencies in the U.S. switched tactics.
The study didn't look specifically at the relationship between accuracy and confidence in courts, where additional time has passed between the crime and the witness' recounting. But the findings indicate that the best practice for obtaining accurate eyewitness identifications in police investigations may be even more nuanced than previously thought.