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Study Shows Disease Prevalence Statistics Sometimes Inflated

Posted on: Monday, 25 April 2005, 15:00 CDT

WASHINGTON - Relax. Grim estimates of how many millions of Americans have various diseases are often as high and wild as a baseball pitcher in spring.

And they're all over the place.

A Baltimore Sun report says 20 million Americans suffer from depression. A patient-care newsletter says 10 million Americans older than 50 have the bone-wasting disease osteoporosis. Other published reports say 13 million Americans have hypothyroidism, 7.9 million are alcoholics, 40 million have the hearing defect known as tinnitus, 62 million have digestive diseases and 70 million have some form of arthritis.

Add up the published claims about disease prevalence and the average American has at least two ailments at a time.

Who's pushing the high numbers? Skeptical bio-statisticians blame drug companies and reporters for much of the hype. They also blame research institutes and disease foundations seeking more public spending on particular diseases.

"They always take the high-end numbers," said Mary Grace Kovar, a senior health statistician at the University of Chicago's National Opinion Research Center in Washington. "They want the money, power and prestige" that flow when a disease looks like a major problem.

Former National Institutes of Health director Dr. Harold Varmus, who's now the president of Memorial Sloan-Kettering Cancer Center in New York, fought hard against using such estimates to justify research spending. He called it "body-based budgeting" and argued that NIH's billions should be targeted instead to areas that promise the greatest scientific and therapeutic advances.

These days, prevalence statistics are often part of a larger effort to persuade people that what they consider a human condition is really a disease. Your grandfather snored. But you - and 18 million other Americans, according to the Sleep Foundation - have a breathing disorder called sleep apnea. Your mother blushed and perspired. But you - and 7 million other Americans - have an excessive sweating disorder called hyperhidrosis, according to the International Hyperhidrosis Society.

Kovar and other bio-statisticians fault reporters for thumping the tub - or worse - to make new diseases newsy.

A case in point: stories about shopping addiction, a vaguely defined compulsion that some drug companies would like to treat with antidepressants.

According to the Atlanta Journal-Constitution, 17 million Americans are compulsive shoppers. A doctor on the British Broadcasting Corp.'s popular health Web site (www.bbc.co.uk/health) says it's 15 million. Ronald Faber, a University of Minnesota Twin Cities professor whose 1992 study provided the high-end figures for both articles, begs to differ. Faber said reporters almost always ignore his report's conclusion that the low-end estimate of 2 million to 4 million was the better one.

"Everybody wants the topic they're talking about to sound important," Faber said in an interview. "To get the story read, you need to grab people's attention, and big numbers grab attention."

Daniel Zelterman, a biostatistics professor at Yale University Medical School in New Haven, Conn., said all the ominous health numbers obscured the real bottom line: "People are living longer. We're living better. Things are looking up, looking good, as far as health is concerned."

Zelterman's theory is that prevalence statistics routinely are skewed by the researcher's motive: "Do you want to say we're winning the war on cancer or that we need more research?"

There's plenty of room for subjectivity, given the way most of these numbers are generated: A researcher selects a random population of several thousand or less and asks a series of carefully worded questions. To the answers, the researcher applies one of several official definitions of a disease and determines approximately how many people in the test group have it. This estimate is expressed as a range and projected onto a much larger population.

Reporters and patients' lobbies often seize the range's high end, drop the low end and hype the disease's prevalence with statements such as "Researchers estimate that as many as 30 million. ..."

Even from authoritative, disease-specialist institutes such as NIH, "you're much more likely to get an overestimate than an underestimate" of a disease's prevalence, said Susan Ellenberg, a professor of biostatistics at the University of Pennsylvania School of Medicine in Philadelphia.

The reason: "The more people who have something, the more likely they'll get funding for it," Ellenberg said.

"Most people at NIH institutes have more of a sense of moral responsibility than to do that," said Ronald Manderscheid, a top health-data expert at the federal Substance Abuse and Mental Health Services Administration.

While some disease foundations use high-end estimates, not all of them do. The American Cancer Society, for example, omits from its figures on cancer's prevalence the minor skin cancers and slow- growing tumors that pose no health threats. Were it raising alarms, it would count them.

According to bio-statistician John Bailar, an adviser to the National Academy of Sciences, prevalence numbers are so untrustworthy that he and his colleagues usually ignore them. Estimates based on doctors' reports or mortality statistics derived from death certificates are more reliable, he said.

Source: Advocate; Baton Rouge, La.

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