Do We Really Know What Makes Us Healthy?
The Sunday New York Times had an article which at first I thought I wasn’t going to like at all, but which turned out to be fascinating.
It described several factors that can confound prospective epidemiologic studies, especially those that report risks or benefits in mere tens of a percent (+10%, -20%), arguing for extreme caution when these claims are not backed up by clincial trials, where they are so frequently shown to be wildly wrong:
The Healthy-User Bias:
…people who faithfully engage in activities that are good for them — taking a drug as prescribed, for instance, or eating what they believe is a healthy diet — are fundamentally different from those who don’t. One thing epidemiologists have established with certainty, for example, is that women who take [hormone replacement therapy] differ from those who don’t in many ways, virtually all of which associate with lower heart-disease risk: they’re thinner; they have fewer risk factors for heart disease to begin with; they tend to be more educated and wealthier; to exercise more; and to be generally more health conscious.
The Compliance Effect:
…people who comply with their doctors’ orders when given a prescription are different and healthier than people who don’t.
The lesson comes from an ambitious clinical trial called the Coronary Drug Project that set out in the 1970s to test whether any of five different drugs might prevent heart attacks…
As it turned out, those men who said they took more than 80 percent of the pills prescribed fared substantially better than those who didn’t. Only 15 percent of these faithful “adherers” died, compared with almost 25 percent of what the project researchers called “poor adherers.” This might have been taken as reason to believe that clofibrate actually did cut heart-disease deaths almost by half, but then the researchers looked at those men who faithfully took their placebos. And those men, too, seemed to benefit from adhering closely to their prescription: only 15 percent of them died compared with 28 percent who were less conscientious. “So faithfully taking the placebo cuts the death rate by a factor of two,” says David Freedman, a professor of statistics at the University of California, Berkeley. “How can this be? Well, people who take their placebo regularly are just different than the others. The rest is a little speculative. Maybe they take better care of themselves in general. But this compliance effect is quite a big effect.”
The Prescriber Effect:
“A physician is not going to take somebody either dying of metastatic cancer or in a persistent vegetative state or with end-stage neurologic disease and say, ‘Let’s get that cholesterol down, Mrs. Jones.’ The consequence of that, multiplied over tens of thousands of physicians, is that many people who end up on statins are a lot healthier than the people to whom these doctors do not give statins…”
– Jerry Avorn, Harvard epidemiologist.
Read the Full Story in the New York Times:
“Do We Really Know What Makes Us Healthy?”
By Gary Taubes
September 16, 2007
Stephen wrote:
Doesn’t it just spook you whenever you read the placebo effect? I mean you gobble down sugar pills and you get something close to the medication benefit. Just wish we could tap into that at will whenever we are ill.
Posted 18 Sep 2007 at 2:18 pm ¶
Tom Chappell wrote:
It is spooky, though this article is mostly talking about fundamental differences between the patients that are being missed by the authors of these studies, as I read it.
For example, a patient who is carefully taking his placebo without fail may also be drinking only moderately, no more than 2 drinks on any one day, say, which your questionnaire may not be catching (perhaps you’re only asking how many drinks a week, and missing the lack of a binge).
And so on and on, a dozen little things that he does to try to be a little more healthy, and you try to account for them in your study, but not very successfully, so far, I guess.
Posted 19 Sep 2007 at 7:38 am ¶