Diet and Fat: A Scientific Consensus Gone Wrong

Everybody "knows" that fat is bad for you, just as they "know" that global warming is caused by human activity. The problem is that fat isn't bad for you, despite the fact that in the 1970s 92 percent of the world's leading doctors claimed it was. In 1988 Surgeon General C. Everett Koop even claimed that, “The depth of the science base underlying its [his report's] findings is even more impressive than that for tobacco and health in 1964.”

It may seem bizarre that a surgeon general could go so wrong. After all, wasn’t it his job to express the scientific consensus? But that was the problem. Dr. Koop was expressing the consensus. He, like the architects of the federal “food pyramid” telling Americans what to eat, went wrong by listening to everyone else. He was caught in what social scientists call a cascade.We like to think that people improve their judgment by putting their minds together, and sometimes they do. The studio audience at “Who Wants to Be a Millionaire” usually votes for the right answer. But suppose, instead of the audience members voting silently in unison, they voted out loud one after another. And suppose the first person gets it wrong.

If the second person isn’t sure of the answer, he’s liable to go along with the first person’s guess. By then, even if the third person suspects another answer is right, she’s more liable to go along just because she assumes the first two together know more than she does. Thus begins an “informational cascade” as one person after another assumes that the rest can’t all be wrong.

Because of this effect, groups are surprisingly prone to reach mistaken conclusions even when most of the people started out knowing better, according to the economists Sushil Bikhchandani, David Hirshleifer and Ivo Welch. If, say, 60 percent of a group’s members have been given information pointing them to the right answer (while the rest have information pointing to the wrong answer), there is still about a one-in-three chance that the group will cascade to a mistaken consensus. Read more

When the global warmers try to stampede the public with threats, intimidation, and claims that the science is "settled" into give them to power to control society, we need to remember that consensus can be wrong, particularly when it's arrived at publicly.