Because Gary Taubes is probably the country’s best health journalist, his article in today’s NY Times Magazine (“Do We Really Know What Makes Us Healthy?”) about the perils of epidemiology especially interested me. It’s the best article on the subject I’ve read. He does a good job explaining what’s called the healthy-user bias — people who take Medicine X tend to make other healthy choices as well. Does wine reduce heart attacks? Well, probably — but people who drink more wine also eat more fruits and vegetables.
The article falls short in two big ways. Taubes does a terrible job presenting the case for epidemiology. He mentions the discovery that smoking causes lung cancer but then disparages it by quoting someone calling it “turkey shoot” epidemiology. Actually, that discovery did more for public health than any clinical trial or laboratory experiment I can think of. Taubes fails to mention the discovery that too-little folate in a pregnant woman’s diet causes neural-tube and other birth defects. As the dean of a school of public health put it in a talk, that one discovery justified all the money ever spent on schools of public health (where epidemiology is taught). Taubes also fails to mention that some sorts of epidemiology are much less error-prone than the studies he talks about. For example, a county-by-county study of cancer rates in the United States showed a big change across a geological fault line. People on one side of the line were eating more selenium than people on the other side. Experiments have left no doubt that too-little selenium in your diet causes cancer.
Even worse, Taubes shows no understanding of the big picture. Above all, epidemiology is a way to generate new ideas. Clinical trials are a way to test new ideas. To complain that epidemiology has led to many ideas that turned out to be wrong — or to write a long article about it — is like complaining that you can’t take a bike on the highway. That’s not what bikes are for. If only 10% of the ideas generated by epidemiology turn out to be correct, well, 10% is more than zero. Taubes should have asked everyone he interviewed “Is there a better way to generate new ideas?” Judging from his article, he asked no one.
Now excuse me to take a selenium pill . . .