How the Streetlight Effect keeps scientists in the dark

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It seems that streetlights make not only a way to be wrong a scientific phenomenon, but a handy metaphor for being wrong about science in general. The Streetlight Effect is a bias in scientific research that costs time, money, and occasionally, lives.

The Streetlight Effect got its start as a joke. A police officer is patrolling when he sees a man, disheveled and reeking of booze, crawling around under a streetlight. The officer walks over and asks what the problem is. The drunk turns and says he dropped the keys to his car and he's trying to find them. The officer glances around, sees nothing in the light from the streetlight, and asks the drunk where exactly he dropped them. The drunk points across the street, near a darkened building. When the police officer asks the drunk why he's looking for his keys all the way over here, the guy replies, "Because the light's better over here."


To be fair, at least the guy knew that the keys definitely were somewhere. Scientists have no way of knowing that the answer to a certain scientific question lies in one particular area of study. They sometimes don't know if there is an answer to be had at all. Still, there is a marked tendency in science (and in other areas) to look where it's easiest to get an answer, even if it's not the area where it's easiest to get the answer. It's not altogether a bad idea. Sometimes grabbing the information that's available instead of wading around in the dark can help more than indefinitely trudging through a mostly-unknown science, but if the effect is unacknowledged there can be massive problems. At one point, an drug that kept a patient's heartbeat steady after a heart attack was a great success. Doctors had long known that patients with unsteady hearbeats were at more risk of dying than those with steady ones. The drug did just what it professed to do, and it did it so well that it was ten years before doctors noticed that people on the drug survived at one third the rate of those not on the drug. A steady heartbeat on one patient was easily measurable. The overall death rate for many patients in many hospitals across the country was not. This is also why simple measures are proposed as cure-alls and then quickly refuted. They were not cure-alls, but they were simple, and thus easy to measure, blinding researchers to other factors.

We're all sometimes guilty of letting our hopes get ahead of our heads and taking the chance that we'll find the best solution in the place that's easiest to search. For most, it doesn't have such dire consequences. Occasionally, though, we have to acknowledge that we're not lucky enough to find truth coupled with ease.


Via Discover and Wrong: Why Experts Keep Failing Us.