The case of Brandon Mayfield, the Portland, Oregon lawyer arrested then exonerated by the FBI for allegedly participating in the Madrid bombings carries with it some important lessons for using science in decision making.

David Feige, public defender in the South Bronx and a Soros media fellow, distills some of these lessons in a column for Slate.

Among those lessons:

Certainty does not equal accuracy.
Consensus does not equal truth.
Never forget underlying assumptions.
Science does not equal decision making.
Science in fact over-determines decisions. (Sorry for the jargon, for an explanation, see my post on Excess of Objectivity.)

An excerpt from Feige’s column:

“But one of the most frightening consequences of the Mayfield incident is the bureau’s attempt to explain away Mayfield’s total misidentification by blaming it on a bad digital print. The reality is that it’s not the print that’s bad, it’s the science…

How many [finger prints] constitute a match? The rather unscientific answer is, it depends. Some police departments require 10, others 12, some are satisfied with eight. This lack of uniformity can mean that one agency (the FBI, say) may declare a print match while another (the Spanish National Police, say) says no. Ultimately, as Simon Cole, the author of Suspect Identities: A History of Fingerprinting and Criminal Identification explains—and the FBI acknowledges—the decision to declare a match is a subjective one, based on the totality of the circumstances and the examiner’s knowledge and experience.

Those subjective decisions mean that that the government can profess certainty and still be dead wrong. Without agreement on essential baseline standards, fingerprinting will remain a practice rather than a science. Make no mistake about it, fingerprints are valuable forensic evidence, based on unique biometric data. But when the evaluation of that data rests on a because-I said-so analysis, the door is wide open for injustice. And as Brandon Mayfield’s case amply demonstrates, taking the government’s say-so as definitive simply isn’t enough. And when psudeoscience is turned loose in the context of the war on terror, the results may well terrify.”