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e-Medical
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Some nights
the newscasts make it seem unsafe to eat, breathe,
exercise or sit still. Yet even as the number of hazards
in our daily lives seems to be multiplying, reports of
treatment breakthroughs and advances in scientific
understanding abound. It may be tempting to discount the
warnings when danger seems all around us, yet should we
also discount the good news? The answer in many cases is
"yes" to both.
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In fact, some of the
dramatic risks and breakthroughs you may hear about are not so
impressive when you consider three common pitfalls in how medical news
is reported and interpreted:
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An association
between a possible risk factor and a disease is often mistakenly
assumed to mean that the risk factor causes the disease.
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Relative risk (that
is, your risk in relationship to the risk of others) is reported
without mention of absolute risk.
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Preliminary
research is assumed to be the last word.
The
Difference Between Association And Cause
Take a recent study
that found an increased risk of breast cancer among women older than
65 with high bone density. If you read only the headline or briefly
glance at the article, it might appear that high bone density causes
breast cancer. Yet high bone density has generally been viewed as a
good thing because it helps to avoid the complications of
osteoporosis, a disorder of low bone density in which hip, wrist and
spine fractures may occur. Does this mean a woman should strive for
high bone density, which may put her at risk of breast cancer, or
should she accept low density and osteoporosis?
A more complete reading
of the story sorts this out. "Bone density … is not a cause of
breast cancer but it is an indirect measure of levels of hormone such
as testosterone and estrogen that have been linked both to bone
density and to breast cancer" - The real news of this report is
that higher bone density is associated with an increased risk of
breast cancer (and may help predict its development) and not that
higher bone density will cause breast cancer.
Relative
-vs- Absolute Risk
Consider the near panic
over phenylpropanolamine (PPA) in the fall of 2000 — many news
outlets reported a dramatic increase in the risk of stroke among
patients taking this medication, which is an ingredient in appetite
suppressants and many over-the-counter cold remedies. According to a
study summarized on the news, a woman taking PPA for a cold tripled
her risk of stroke; the risk was even higher if she took PPA in the
form of an appetite suppressant.
Although that sounds
bad, realize that this is a relative risk - one risk (that of
women taking PPA) compared with another (that of women not taking PPA).
The absolute risk of developing a stroke while taking PPA is
estimated at one or two in a million. Although PPA appears to increase
the risk of stroke, the chances of PPA causing serious harm when taken
for cold symptoms are quite small.
Preliminary
Research And Cautious Optimism
Most medical advances
are realized gradually. Well before a definitive study can demonstrate
safety and effectiveness in people, studies in animals and small
trials in humans are required. These small, preliminary studies are
critical because many drugs or treatments do not deliver on their
early promises.
For this reason, many
reports of breakthroughs that are based on small, preliminary studies
do not deserve the publicity and excitement they generate. Although
cautious optimism may be entirely appropriate, it is not always easy
to see past the pronouncements of "cures" and "major
findings."
The
Bottom Line
At its best, medical
news keeps us updated on the latest advances in maintaining health and
fighting disease. But sometimes it generates or perpetuates medical
myths by overestimating the importance of research findings.
You can be better
informed by remembering the difference between:
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An
association and a cause
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By
looking for absolute (not just relative) risk in the story
and;
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By
recognizing that there is a good reason many medical reports sign
off with a familiar phrase: "More study is needed.
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