Understanding Scientific Consensus

The NYT has an interesting article on a recent scientific consensus that was wrong in nearly all of its particulars.

In 1988, the surgeon general, C. Everett Koop, proclaimed ice cream to a be public-health menace right up there with cigarettes. Alluding to his office’s famous 1964 report on the perils of smoking, Dr. Koop announced that the American diet was a problem of “comparable” magnitude, chiefly because of the high-fat foods that were causing coronary heart disease and other deadly ailments.

He introduced his report with these words: “The depth of the science base underlying its findings is even more impressive than that for tobacco and health in 1964.”

That was a ludicrous statement, as Gary Taubes demonstrates in his new book meticulously debunking diet myths, “Good Calories, Bad Calories” (Knopf, 2007). The notion that fatty foods shorten your life began as a hypothesis based on dubious assumptions and data; when scientists tried to confirm it they failed repeatedly. The evidence against Häagen-Dazs was nothing like the evidence against Marlboros.

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.

This idea of a "cascade" is important because it explains a lot of what is going on in contemporary science.

Because of this effect, groups are surprisingly prone to reach mistaken conclusions even when most of the people started out knowing better.... 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.

Cascades are especially common in medicine as doctors take their cues from others, leading them to overdiagnose some faddish ailments (called bandwagon diseases) and overprescribe certain treatments (like the tonsillectomies once popular for children). Unable to keep up with the volume of research, doctors look for guidance from an expert — or at least someone who sounds confident.

Read the whole thing here.

The article goes on to show the formation of the consensus, the ostracism of dissenting scientists, and the disastrous public policies based upon the false consensus, all of which is extremely reminiscent of what is happening today in environmental science and the global warming debate. We should remember that "science" is conducted by human beings with all the weakness and fallibility that entails, and that credentialed "experts" are often disastrously wrong. With that in mind we should recognize that expert opinion is a weak and shifting base on which to construct public policy.