Sagittarians are 38% more likely to break a leg than people of other star signs -- and Leos are 15% more likely to suffer from internal bleeding. So says a 2006 Canadian study that looked at the reasons residents of Ontario province had unplanned stays in the hospital.
Leos, Sagittarians: There's no need to worry. Even the study's authors don't believe their results.
They're illustrating a point -- that a scientific approach used in many human studies often leads to findings that are flat-out wrong.
Such studies make headlines every day, and often, as the public knows too well, they contradict each other. One week we may hear that pets are good for your health, the next week that they aren't. One month, cellphone use causes brain cancer; the next month, it doesn't.
"It's the cure of the week or the killer of the week, the danger of the week," says Dr. Barry Kramer, associate director for disease prevention at the National Institutes of Health in Bethesda, Md. It's like treating people to an endless regimen of whiplash, he says.
Take the case of just one item: coffee. Drinking two or three cups per day can triple the risk of pancreatic cancer, according to a 1981 study. Not so, concluded a larger follow-up study published in 2001.
Coffee reduces the risk of colorectal cancer, found a 1998 study. Not so, according to one published later, in 2005.
"I've seen so many contradictory studies with coffee that I've come to ignore them all," says Donald Berry, chair of the department of biostatistics at the University of Texas MD Anderson Cancer Center in Houston.
"What about the man on the street?" asks Stan Young, a statistician at the National Institute of Statistical Sciences in Research Triangle Park, N.C. "He reads about coffee causing and not causing cancer -- so many contradictory findings he begins to think, 'I don't trust anything these scientists are saying.' "
These critics say the reason this keeps happening is simple: Far too many of these epidemiological studies -- in which the habits and other factors of large populations of people are tracked, sometimes for years -- are wrong and should be ignored.
In fact, some of these critics say, more than half of all epidemiological studies are incorrect.
The studies can be influential. Often, in response to them, members of the public will go out and dose themselves with this vitamin or that foodstuff.
And the studies also influence medical practice -- doctors, the critics note, encouraged women to take hormones after menopause long before their effects were tested in randomized clinical trials, the gold standard of medical research.
Some of epidemiology's critics are calling for stricter standards before such studies get reported in medical journals or in the popular press.
Young, one of the foremost critics, argues that epidemiological studies are so often wrong that they are coming close to being worthless. "We spend a lot of money and we could make claims just as valid as a random number generator," he says.
Epidemiology's defenders say such criticisms are hugely overblown.
They are "quite simplistic and exaggerated," says Dr. Meir Stampfer, a professor of epidemiology and nutrition at the Harvard School of Public Health and a professor of medicine at Harvard Medical School.
What's more, some things simply cannot be tested in randomized clinical trials. In certain cases, to do so would be unethical. (Care to assign half the people in a trial to smoke cigarettes?)
In other cases, a trial of adequate size and duration -- say, to test whether coffee drinking raises or lowers the risk of Parkinson's disease -- would have to control the habits of huge numbers of people for decades. That would not only be hugely expensive but also virtually impossible.
Stampfer cites examples of findings of epidemiology that, he says, have stood the test of time: smoking's link to lung cancer, to name the most notable.
Watching for clues
In epidemiological studies (also called observational studies), scientists observe what's going on -- they don't try to change it. From what they observe, they reach conclusions -- for example, about the risk of developing a certain disease from being exposed to something in the environment, lifestyle or a health intervention.
There are different ways to do this. Cohort studies follow a healthy group of people (with different intakes of, say, coffee) over time and look at who gets a disease. They're considered the strongest type of epidemiological study.
Case-control or retrospective studies examine people with and without a certain disease and compare their prior life -- for how much coffee they drank, for example -- and see if people who got the disease drank more coffee in their past than those who didn't.
Cross-sectional studies compare people's present lifestyle (how much coffee they drink now) with their present health status.