By Brian Carnell

Thursday, May 2, 2002

The New York Times' Gina Kolata recently looked at how a randomized trials of hormone replacement therapy is undermining confidence in epidemiology.

The impetus for this debate was started when 28 prominent scientists and doctors concluded that randomized clinical trials indicate that there is no benefit to HRT. The problem for epidemiology is that numerous epidemiological studies -- including several large, well done studies -- have concluded that HRT offers real benefits to women.

The obvious conclusion is that epidemiological evidence might be far more likely to be erroneous than generally thought. This is especially true with the ongoing obsession over studying extremely small effects (for example, the plethora of studies that report 30 or 40 percent increases in risk). As Kolata writes,

There is a reason the truth is so hard to find, he [Dr. Richard Peto] said. Increasingly, researchers are looking for very small effects like a tiny edge in a battle against heart disease. If an effect is huge like the increased risk that a person who smokes will develop lung cancer, an observational study will correctly find it. If a treatment is truly sensational, Dr. Peto said, its benefits will be so clear that any study, randomized or observational, will find them.

The problems occur in questions like the one on estrogen, he said, "when the effects aren't very big." If there is no effect or just a tiny one, chance comes into play, making one study turn out slightly positive and another slightly negative, and any flaw in a study or its analysis can throw the results into the wrong column.

The best outcome of the debate over the disparate HRT findings might be a more skeptical interpretation and treatment of epidemiological studies that report such small effects.

Source:

In public health, definitive data can be elusive. Gina Kolata, The New York Times, April 23, 2002.

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