False Consensus

This is an interesting article on its own. It seems that there is little evidence that dietary fat is bad. The article traces how a consensus can be wrong. In this case, a diet researcher named Ancel Keys decided in the 1950s that dietary fat was bad. He did an incomplete study to back this up. Because of his prominence, what amounted to personal opinion became scientific consensus despite the fact that several studies have proven otherwise.

This is given as an example of the cascade effect. When multiple people are asked a question as a group, the first one to confidently give an answer can sway someone else who is not sure. This in turn convinces others who think that the majority must have the right answer.

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.

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.

When Keys first announced that fat is bad, the American Heart Association disagreed. Three years later it switched positions, not because of new science, but because Keys and some fellow believers were now in control.

In the 1970s Senator George McGovern's office issued a report suggesting that people cut back on fat consumption. The committee that drew up the report relied on the advice of a single nutritionist.

Meanwhile, there still wasn’t good evidence to warrant recommending a low-fat diet for all Americans, as the National Academy of Sciences noted in a report shortly after the U.S.D.A. guidelines were issued. But the report’s authors were promptly excoriated on Capitol Hill and in the news media for denying a danger that had already been proclaimed by the American Heart Association, the McGovern committee and the U.S.D.A.

The scientists, despite their impressive credentials, were accused of bias because some of them had done research financed by the food industry. And so the informational cascade morphed into what the economist Timur Kuran calls a reputational cascade, in which it becomes a career risk for dissidents to question the popular wisdom.

With skeptical scientists ostracized, the public debate and research agenda became dominated by the fat-is-bad school. Later the National Institutes of Health would hold a “consensus conference” that concluded there was “no doubt” that low-fat diets “will afford significant protection against coronary heart disease” for every American over the age of 2. The American Cancer Society and the surgeon general recommended a low-fat diet to prevent cancer.

All of this is interesting on its own but there are obvious parallels with global warming. In the case of warming, the confident voice belongs to Dr. James Hansen of NASA. In 1988 he convnced Congress that global warming was not only real, it was responsible for a heat wave gripping the country at the time. Congress authorized millions (which has since grown into billions) for research. If cascades can happen on their own, imagine the influence of so much cash.

Then there is the "reputational cascade". The background of anyone skeptical about global warming is examined to see if the skeptic ever received a penny from an oil company. If he did then he is denounced as an oil company mouthpiece and ignored.

The existence of the cascade effect does not prove the global warming is not happening but it should serve as a warning against placing too much faith in scientific consensus.