Introduction, Part V

I began this Introduction with an example of a group solving a simple problem: figuring out the weight of an ox. I'll end it with an example of a group solving an incredibly complex problem: locating a lost submarine. The differences between the two cases are immense. But the principle in each is the same.

In May 1968, the U.S. submarine Scorpion disappeared on its way back to Newport News after a tour of duty in the North Atlantic. Although the navy knew the sub’s last reported location, it had no idea what had happened to the Scorpion, and only the vaguest sense ofhow far it might have traveled after it had last made radio contact. As a result, the area where the navy began searching for the Scorpion was a circle twenty miles wide and many thousands of feet deep. You could not imagine a morehopeless task. The only possible solution, one might have thought, was to track down three or four top experts on submarines and ocean currents, ask them where they thought the Scorpion was, and search there. But, as Sherry Sontag and Christopher Drew recount in their book Blind Mans Bluff a naval officer named John Craven had a different plan.

First, Craven concocted a series of scenarios—alternative explanations for what might have happened to the Scorpion. Then he assembleda team of men with a wide range of knowledge, including mathematicians, submarine specialists, and salvage men. Instead of asking them to consult with each other to come up with an answer, he asked each of them to offer his best guess about how likely each of the scenarios was. To keep things interesting, the guesses were in theform of wagers, with bottles of Chivas Regal as prizes. And so Craven’s men bet on why the submarine ran into trouble, on its speed as it headed to the ocean bottom, on the steepness of its descent, and so forth.

Needless to say no one of these pieces of information could tell Craven where the Scorpion was. But Craven believed that if he put all the answers together, building a composite picture of how the Scorpion died, he’d end up with a pretty good idea of where it was. And that’s exactly what he did. He took all the guesses, and used a formula called Bayes’s theorem to estimate the Scorpion’s final location. (Bayes’s theorem is a way of calculating how new information about an event changes your preexisting expectations of how likely the event was.) When he was done, Craven had what was, roughly speaking, the group’s collective estimate of where the submarine was.

The location that Craven came up with was not a spot that any individual member of the group had picked. In other words, not one of the members of the group had a picture in his head that matched the one Craven had constructed using the information gathered from all of them. The final estimate was a genuinely collective judgment that the group as a whole had made, as opposed to representing the individual judgment of the smartest people in it. It was also a genuinely brilliant judgment. Five months after the Scorpion disappeared, a navy ship found it. It was 220 yards from where Craven’s group had said it would he.

What’s astonishing about this story is that the evidence that the group was relying on in this case amounted to almost nothing. It was really just tiny scraps of data. No one knew why the submarine sank, no one had any idea how fast it was traveling or how steeply it fell to the ocean floor. And yet even though no one in the group knew any of these things, the group as a whole knew them all.

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