PBS’ Frontline has a new show called The Real CSI that examines many of the most commonly used criminal forensics techniques and shows the problems and limits of how useful they are. In a segment just released from the show, they look at a study about cognitive biases in fingerprint analysis:
In 2004, cognitive neoroscientist Itiel Dror set out to examine whether the process of fingerprint analysis, long considered one of the most reliable forms of forensic science, can be biased by the knowledge examiners have when they attempt to find a match for prints from a crime scene.
In the clip above from tomorrow night’s film The Real CSI, FRONTLINE correspondent Lowell Bergman explains the way Dror constructed an experiment using the case of Brandon Mayfield. Mayfield, an Oregon lawyer, was at the center of international controversy in 2004 after the FBI and an independent analyst incorrectly matched his prints to a partial print found on a bag of detonators from the Madrid terrorist bombings.
Dror asked five fingerprint experts to examine what they were told were the erroneously matched prints of Mayfield. In fact, they were re-examining prints from their own past cases. Only one of the experts stuck by their previous judgments. Three reversed their previous decisions and one deemed them “inconclusive.”
Dror’s argument is that these competent and well-meaning experts were swayed by “cognitive bias”: what they knew (or thought they knew) about the case in front of them swayed their analysis.
Which is why the analyst should be entirely isolated from the case, should know nothing about it at all before comparing fingerprints, and should also have to compare the fingerprint to several different prints, not just the one the police think might be a match. That’s how you avoid such cognitive bias. It’s the same principle that should govern police lineups, the officer administering the lineup should not have any idea which person in the lineup is the one the police think committed the crime.