Archives » Tuesday, December 04, 2007
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Sharon Begley
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Dec 4, 2007 04:00 PM
If there are any doctors who are congratulating themselves for basing
their treatment decisions on rigorous clinical evidence--not the
questionable studies on things like homeopathy that my colleague Jerry Adler wrote about in his health column this week--they
can stop. Physicians and even biomedical researchers may say they rely
solely on the gold standard of randomized clinical trials, but they’re
as likely to believe much weaker studies as is the most desperate
cancer patient combing the Web for laetrile.
So finds an alarming study published this afternoon in the Journal of
the American Medical Association. Scientists led by John Ioannidis of
the University of Ioannina School of Medicine in Greece find that
well-known claims based on poor studies are repeated over and over
again in medical journals even when better studies contradict them. The
earlier, refuted conclusions continue to pop up in medical journals
like satanic whack-a-moles.
It’s important to understand why some ways of doing a study are better
than others. Less-good are observational studies. In these, you
basically watch and measure a group of people who are doing something
related to their health--women taking estrogen for menopause, say--and
compare them to a similar group who are not doing that thing. In this
example, observational studies concluded that estrogen reduces women’s
risk of heart disease, Alzheimer’s and other bad things. But then a
rigorous study looked at the same question (the effect of estrogen), by
randomly assigning some women volunteers to take estrogen and others to
take a dummy pill. Lo and behold, estrogen suddenly didn’t look like
such a good idea: it raised the risk of heart disease, stroke and
breast cancer, the Women’s Health Initiative reported in a blockbuster announcement in 2002.
Why the different results in the two kinds of studies? One reason is
that in observational studies, women who chose to take estrogen are
inherently different from women who did not. They were, de facto,
seeing a doctor (for prescriptions if nothing else), and were likely
wealthier and better educated. Those three factors alone, not the
estrogen, might have made them healthier than non-estrogen women,
distorting the results.
The well-publicized negative verdict on estrogen makes it hard for
biomedical researchers to slip a sentence into their papers
off-handedly saying estrogen protects against heart disease. Not so
with other studies. To wit:
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