There’s a very interesting article by John Ioannidis in PLoS Medicine, the free online journal. Most current published research findings might well be false, he says. There are several factors, and I think it’s worth presenting them in detail:
1. Many research studies are small, with only a few dozen participants.This ought to be an eye-opener…. The solution? More publication of preliminary findings, negative studies (which often suffer that fate of the file-drawer effect), confirmations, and refutations. PLoS says, “the editors encourage authors to discuss biases, study limitations, and potential confounding factors. We acknowledge that most studies published should be viewed as hypothesis-generating, rather than conclusive.” And maybe this will also temper journalists’ tendency to offer every new study as the Next Big Thing.
2. In many scientific fields, the “effect sizes” (a measure of how much a risk factor such as smoking increases a person’s risk of disease, or how much a treatment is likely to improve a disease) are small. Research findings are more likely true in scientific fields with large effects, such as the impact of smoking on cancer, than in scientific fields where postulated effects are small, such as genetic risk factors for diseases where many different genes are involved in causation. If the effect sizes are very small in a particular field, says Ioannidis, it is “likely to be plagued by almost ubiquitous false-positive claims.”
3. Financial and other interests and prejudices can also lead to untrue results.
4. “The hotter a scientific field (with more scientific teams involved), the less likely the research findings are to be true,” which may explain why we sometimes see “major excitement followed rapidly by severe disappointments in fields that draw wide attention.”