The Power of Suggestion and Mistaken Fingerprint Identification

Fingerprint analysis is often thought to be a foolproof science -- an opinion Brandon Mayfield doesn't share. Mayfield, you may recall, was detained after the FBI mistakenly determined that his fingerprints were found on a bag linked to the bombing of a train in Madrid.

Research conducted by British psychologist Itiel Dror explains how the power of suggestion can taint the supposedly "foolproof" science of fingerprint identification.

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He has conducted studies that show that when working on an identification, fingerprint examiners can be influenced by what else they know about a case. In one experiment, he found that the same examiner can come to different conclusions about the same fingerprint, if the context is changed over time.

The same kinds of contextual biases arise with other decision-makers, said Dr. Dror, who works with the military and with financial and medical professionals. He thinks one reason forensic examiners often do not acknowledge that they make errors is that in these other fields, the mistakes are obvious. “In forensics, they don’t really see it,” he said. “People go to jail.”

Just as police officers conducting lineups should not be told whether the suspect is or isn't among those who are lining up, forensic scientists who are asked to match a fingerprint shouldn't be told whether the print is suspected to have been left by a particular person. Any other standard raises concerns about the objectivity of the analysis.

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    Wouldn't this be easy to correct? (none / 0) (#1)
    by Jacob Freeze on Tue May 12, 2009 at 04:22:35 PM EST
    Where there's a dispute about fingerprint evidence (which is more or less always), why don't they just ask examiners in other labs to assess the match?

    With two or three dummy sets thrown in to avoid a tendency to confirm whatever your colleagues already decided, it seems like you could arrive at a standard of "inter-subjectivity," even if fingerprint analysis never becomes entirely objective.

    It's called (5.00 / 1) (#4)
    by Zorba on Tue May 12, 2009 at 07:00:48 PM EST
    a "double blind" study in the field of science (see my comment below, with a link to the National Academy of Science's study on forensic data).  It would be easy enough to set up.  The examiners themselves would not know which fingerprints were the suspect's and which were "dummies" (as it were).  They would then compare those prints to the ones found at the scene.  In addition, independent examiners would also be sent the same data in a "blind" examination, to confirm.  Would it cost more?  Sure.  What is the price of justice?  And, even aside from the very real dangers of jailing the wrong person, wouldn't you want to make sure that the actual perpetrator was caught and incarcerated, rather than allowed to roam free and possibly commit other crimes?  I certainly would.  And I have a real problem with imprisoning the innocent, as well.  Better that ten guilty persons go free than that one innocent person is punished.  (But I may be one of a minority that feels this way, at least in society at large.)

    But think of the costs! (none / 0) (#2)
    by caseyOR on Tue May 12, 2009 at 06:03:45 PM EST
    Rape kits are sitting on shelves at police departments because, these police departments claim, there is no money to have them analyzed. I don't buy it, but I am pretty sure local law enforcement would not be any more interested in paying to have fingerprints analyzed more than the once.

    Didn't the (none / 0) (#3)
    by Zorba on Tue May 12, 2009 at 06:18:02 PM EST
    National Academy of Science's National Research Council recently release results of their extensive study about the (un)reliability of forensic data? Yes, indeed they did.  Fingerprint analysis, and other such, needs to be looked at very carefully.  See:
    (And don't believe everything the police tell you- it's not all as "cut and dried" and scientific as "CSI" and "Law and Order" would have you believe.  Always verify.)