Invoking the children of fictional Lake Wobegon, who are all – impossibly – above average, a pair of researchers reminds us that most patients have below-average odds of getting most illnesses and of benefiting from most treatments.

That's the argument laid out by Andrew Vickers and Dr. David Kent in the Annals of Internal Medicine in an essay cautioning against doing too much screening for disease and treating too many people unnecessarily based on the results.

"We can work out ways to be smarter about screening and prevention," Vickers, a researcher at Memorial Sloan Kettering Cancer Center in New York, said by email. "If we are more sophisticated about working out risk for individuals, then we can better advise them as to whether prevention and screening would lower their risk enough to make it worth it for them."

Take lung cancer, for example. The risk for a typical American of developing this at some point is about 7.5 percent. But really, the risk for smokers is as high as 20 percent and the risk for nonsmokers is about 1 percent.

"Lung cancer screening isn't even recommended for all smokers, let alone nonsmokers," Vickers said. "Screening generally does more harm than good for people who are at low risk."

While that's a fairly clear-cut case, the discussion about risks and benefits for treatment get murkier with other conditions, such as prostate cancer or heart disease, he said.

Typical approaches to prostate cancer screening, which assume that all men are at average risk, can lead to over-diagnosis as well as side effects such as impotence and incontinence from the tests to identify malignancies, Vickers and Kent note in their essay.

Testing for prostate-specific antigen (PSA), a protein produced in higher quantities by tumor cells, has only modestly reduced deaths from the disease but dramatically increased diagnosis and treatment, the authors point out.

Men who have the highest PSA levels at age 60 are about 20 times more likely to die from the disease than men with the lowest amounts of this protein, and almost all deaths by age 85 occur in this group of men with the biggest risk.

"The reason why over-detection of prostate cancer is a problem is that management of prostate cancer can have major side effects and complications, no matter what the treatment is," said Dr. Ian Thompson Jr., director of the Cancer Therapy and Research Center at the University of Texas Health Science Center in San Antonio.

"Most tumors are very small and so slow-growing that the man rarely will even notice them in his lifetime," said Thompson, who wasn't involved in the study. "If a man has a slow-growing prostate cancer and opts to just watch it, it's still a nuisance with multiple office visits, blood tests, and repeated prostate biopsies," Thompson said in an email.

Vickers makes a similar case for giving drugs to prevent heart attacks to healthy people with high cholesterol who have never had a heart attack before.

For a person who has a 20 percent risk of a heart attack over the next decade, taking a pill to cut that risk in half, to just 10 percent, may be worth any side effects that accompany the medication, Vickers said.

But for somebody with just a 4 percent risk, halving that to 2 percent may not be worth the side effects of taking the pill, he said.

"The essence of the message is that physicians and patients should be careful to suggest or request screening, prevention, or treatment interventions and that they should be considered carefully based on the available evidence for that particular patient," Thompson said. "In many cases, part of that personalization will include a discussion of the patient's priorities."