Boris pointed me to this article by Robert Lee Hotz:
We all make mistakes and, if you believe medical scholar John Ioannidis, scientists make more than their fair share. By his calculations, most published research findings are wrong. . . . “There is an increasing concern that in modern research, false findings may be the majority or even the vast majority of published research claims,” Dr. Ioannidis said. “A new claim about a research finding is more likely to be false than true.”
The hotter the field of research the more likely its published findings should be viewed skeptically, he determined.
Take the discovery that the risk of disease may vary between men and women, depending on their genes. Studies have prominently reported such sex differences for hypertension, schizophrenia and multiple sclerosis, as well as lung cancer and heart attacks. In research published last month in the Journal of the American Medical Association, Dr. Ioannidis and his colleagues analyzed 432 published research claims concerning gender and genes.
Upon closer scrutiny, almost none of them held up. Only one was replicated. . . .
Ioannides attributes this to “messing around with the data to find anything that seems significant,” and that’s probably part of it. The other part is that, even if all statistics are done according to plan, the estimates that survive significance testing will tend to be large–this is what we call “Type M error.” See here for more discussion.