Mathematician John Allen Paulos on the confirmation-bias dangers of FISA:
Having so much unfiltered information (phone records, emails, internet searches, travel itineraries, financial statements, Facebook postings, credit card bills, etcetera) with which to work and having no requirement for specific focus or judicial warrant, any wild hunch or obsession can be pursued relentlessly without fear of disconfirmation.
The resulting combinatorial explosion of connections and interconnections will always provide ample raw material for the development of any investigative group’s pet theory. If, for example, there are 400,000 Americans (and a million names) on the terrorist watch list, as the ACLU announced last month, then there are about 80 billion pairs of possible co-conspirators on the list and more than 10 quadrillion possible threesomes on the list. Search this large “party” diligently enough for confirmatory Yesses and ignore willfully enough disconfirmatory Noes, and who knows what will result.
I had a similar thought recently while watching 2007’s Zodiac on late-night HBO. The movie’s central thread is that the killer really was Arthur Leigh Allen, a heavyset pedophile who said all kinds of suggestive things when detectives first interviewed him and who kept turning out to have more extremely improbable circumstantial evidence against him, and whom the police made their lead suspect for years without ever producing anything really incriminating. In the movie, Jake Gyllenhaal finally confronts Allen in the hardware store where he’s working, looks him in the eye, and knows in his heart that Allen was the killer.
What the movie doesn’t tell you is that in the early 1990s, after Allen died, DNA testing on envelopes sent by the Zodiac killer to the San Francisco Chronicle conclusively showed that Allen was not the guy who mailed them. The thing is, the police investigated 2500 suspects in the Zodiac killer case. When you investigate that many people, each of whom has already been picked for some reason, you are mathematically certain to get one guy whose background is chock full of so many incredible coincidental suspicious events and connections that he just has to be the guy who did it. I mean, Allen had lived in his mother’s basement just 50 yards from the diner where one of the victims worked, and he’d had bloody knives in his car on the day she was stabbed, which he claimed were from killing chickens. Come on — what are the odds? Well, if you’re looking at a population of people who’ve been selected because they’re suspiciously connected to the murders, it’s quite possible that the odds are about 2500 to 1, and that it doesn’t actually mean anything at all.
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