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<a href="http://www.nytimes.com/"><img src="http://graphics8.nytimes.com/images/misc/nytlogo153x23.gif" alt="The New York Times" align="left" border="0" hspace="0" vspace="0"></a>
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<div class="">January 28, 2013</div>
<h1>A Crash Course in Playing the Numbers</h1>
<h6 class="">By
<span><span>ABIGAIL ZUGER, M.D.</span></span></h6>
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<p>
The chances are that you turn to this part of the newspaper in search of
some reliable tools for optimizing your health. The chances are that
you periodically visit a doctor for the same reason. </p>
<p>
Alas, what you seek cannot be found in either place, not if it’s
certitude you’re after. Whether you are healthy, moribund or traversing
the stages of decrepitude in between, every morsel of medical advice you
receive is pure conjecture — educated guesswork perhaps, but guesswork
nonetheless. Your health care provider and your favorite columnist are
both mere croupiers, enablers for your health <a href="http://health.nytimes.com/health/guides/disease/pathological-gambling/overview.html?inline=nyt-classifier" title="In-depth reference and news articles about Pathological gambling." class="">gambling</a> habit. </p>
<p>
Staying well is all about probability and risk. So is the interpretation
of medical tests, and so are all treatments for all illnesses, dire and
trivial alike. Health has nothing in common with the laws of physics
and everything in common with lottery cards, mutual funds and tomorrow’s
weather forecast. </p>
<p>
Thus, no matter how many vitamin-based, colon-cleansing, fat-busting
diet and exercise books show up in 2013, the most important health book
of the year is likely to remain Charles Wheelan’s sparkling and
intensely readable “Naked Statistics,” even though it’s not primarily
about health. </p>
<p>
A professor of public policy and economics at Dartmouth, Mr. Wheelan
earned journalism credentials writing for The Economist and has
previously drawn on both careers to produce <a title="Blog post from the Magazine of The Times." href="http://6thfloor.blogs.nytimes.com/2012/09/28/how-to-read-like-an-economics-columnist/">“Naked Economics”</a>
(2002), an accessible guide for the lay reader. “Naked Statistics” is
similar, a riff on basic statistics that is neither textbook nor essay
but a happy amalgam of the two. </p>
<p>
It is not the place to learn for the first time about medians and means,
but definitely the place to remember what you were once supposed to
know about these and other key concepts — and, more important, why you
were supposed to know them. </p>
<p>
And that means you. While a great measure of the book’s appeal comes
from Mr. Wheelan’s fluent style — a natural comedian, he is truly the
Dave Barry of the coin toss set — the rest comes from his multiple real
world examples illustrating exactly why even the most reluctant
mathophobe is well advised to achieve a personal understanding of the
statistical underpinnings of life, whether that individual is watching
football on the couch, picking a school for the children or jiggling
anxiously in a hospital admitting office. </p>
<p>
Are you a fan of those handy ranking systems based on performance data,
guaranteed to steer you to the best surgeons in town? If so, you are up
to your armpits in descriptive statistics, and Mr. Wheelan has some
advice for you: beware. The easiest way for doctors to game those
numbers is by avoiding the sickest patients. </p>
<p>
Has a diagnosis of <a href="http://health.nytimes.com/health/guides/disease/cancer/overview.html?inline=nyt-classifier" title="In-depth reference and news articles about Cancer." class="">cancer</a>
in the family sent you fishing around for information on average
survival? You would be well advised to figure out if it is mean or
median survival you’re looking at. </p>
<p>
Mr. Wheelan pays homage to Stephen Jay Gould’s classic essay on prognosis, <a title="Stephen Jay Gould’s essay. " href="http://www.cancerguide.org/median_not_msg.html">“The Median Isn’t the Message,”</a>
in which Dr. Gould uses his own cancer diagnosis to illustrate how
misleading median-survival data can be. (Told he had a malignancy with a
median survival of eight months, Dr. Gould died of an unrelated cancer
two decades later.) </p>
<p>
Are you impressed with studies showing that people who take Vitamin X or
perform Exercise Y live longer? Remember, correlation does not imply
causation. Do you obsess over studies claiming to show that various
dietary patterns cause cancer? In fact, Mr. Wheelan points out, this
kind of research examines not so much how diet affects the likelihood of
cancer as how getting cancer affects people’s memory of what they used
to eat. </p>
<p>
And while we’re talking about bias, let’s not forget publication bias:
studies that show a drug works get published, but those showing a drug
does nothing tend to disappear. </p>
<p>
Do you think you need a yearly PET scan to check for rare diseases? Mr.
Wheelan has you contemplate the spam filter on your e-mail program. Set
too low, it feeds a lot of garbage into your in-box; set too high, it
will make you miss the important messages. The same trade-off applies to
the interpretation of medical tests. Unproven disease screens are
likely to do little but feed lots of costly, anxiety-producing garbage
into your medical record. </p>
<p>
Mr. Wheelan deftly whisks you through mean distributions and standard
errors, and before you know it you have plunged into the dense thickets
of regression analysis, a tool for separating out many different strands
of cause and effect. With the aid of a long shaggy-dog story involving a
group of whippet-thin marathon runners and a handful of considerably
plumper delegates to an International Festival of Sausage, you will
undoubtedly get closer than ever to understanding the powerful technique
he calls “the hydrogen bomb of statistics.” </p>
<p>
Regression analysis is the engine that drives the giant randomized
controlled studies that increasingly inform every medical decision
anyone makes for you these days. It can be a force for good or for ill,
and Mr. Wheelan aptly demonstrates how it can succeed and how it can
fail (note, for instance, the recent gigantic flip-flops on <a href="http://topics.nytimes.com/top/news/health/diseasesconditionsandhealthtopics/estrogen/index.html?inline=nyt-classifier" title="Recent and archival health news about estrogen." class="">estrogen</a> prescribing). </p>
<p>
If you want to eat sausage and survive, you should know what goes on in
the factory. That dictum — one of only a few certainties in an uncertain
world — most definitely applies to the statistical sausage factory
where medical data is ground into advice. Mr. Wheelan has propped the
factory gates wide open. Take his tour. </p>
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<br clear="all"><br>-- <br>Art Deco (Wayne A. Fox)<br><a href="mailto:art.deco.studios@gmail.com" target="_blank">art.deco.studios@gmail.com</a><br><br><img src="http://users.moscow.com/waf/WP%20Fox%2001.jpg"><br>
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