5 Ways to Size Up a Health Risk

Don't let misleading stats from doctors and the news lead you astray.

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Imagine being in a room with a mosquito. Now imagine another mosquito enters the room. Technically, your risk of getting bitten has just doubled. Should you be twice as worried? Maybe. But imagine that the room is the size of the Superdome. How worrisome is that doubling now? For most people, the elevated risk would be nearly meaningless.

When it comes to making decisions that are critical to our health, we often aren't told the size of the metaphorical room. A doctor or a news article might inform you that some unhealthy influence will double your risk of getting sick, or that some treatment will make you 30 percent more likely to feel better, but you don't always hear how big the risk was to begin with or how likely you'd be to recover without the treatment.

Pin that doctor or the medical reporter down, however, and you might learn that clean-sounding ratios and percentages sometimes belie a rather messy reality—that there's a great deal of uncertainty in the medical studies that doctors use to determine care. That's the gist of The Illusion of Certainty: Health Benefits and Risks, a book that argues that this layer of uncertainty makes medical decisions as much an art as a science. To make wise choices, argues Erik Rifkin, one of the book's authors, patients must be adept at spotting misleading facts and figures. Here are five strategies that can help.

When considering a medical procedure or drug treatment, make sure you understand the associated benefits in absolute—not relative—terms. In the mosquito example above, the appearance of the second mosquito doubles the relative risk (upping that risk by 100 percent), but it hardly increases the absolute risk. To get a sense of the absolute risk, ask your doctor what would happen to 1,000 people who decided to have the treatment and another 1,000 who decided not to have it. She should be able to tell you how many people in each group would have positive (or negative) outcomes—numbers that you can then compare head to head. The comparison might surprise you. For example, says Rifkin, men who don't get PSA tests live just as long as men who do, even though PSA screening catches prostate tumors early.

Find out the absolute risks associated with any medical procedure you consider. Using the same strategy as above, find out how many people in each thousand-person group would experience adverse side effects. Once you have the absolute benefits and risks straight, you'll have a better chance of comparing apples with apples. You may find that some of the treatments you thought would help a lot might actually offer only minimal benefits. The risks of some cholesterol-lowering statin drugs may outweigh the benefits among people who experience strong adverse side effects, for example. Likewise, a full-body CT scan doses the body with radiation that could cause later cancers without providing any clear benefits.

Consider whether you're facing a risk that you chose willingly or whether some larger force pushed the risk on you without your consent. People tend to underestimate risks when they choose them, while they tend to exaggerate those risks forced upon them, Rifkin says. You might find yourself outraged over air pollution caused by traffic fumes while indifferent about the risks caused by similar pollutants from the candle you choose to burn during dinnertime, for example. Whether you're willing to get a particular medical procedure or change your behavior to avoid a potential risk may be as dependent on how that risk originated as it is on the actual amount of danger—and that's worth knowing before you drop a lot of money or go way out of your way to remedy a minuscule risk that you didn't bring on yourself.

When your doctor suggests a new, technologically advanced procedure or drug over an old one, ask how many more people out of 1,000 would benefit from the former, from the latter, or from no treatment at all. The financial incentives in our medical system, Rifkin says,may encourage physicians to prescribe new, sophisticated treatments—even if there is no solid evidence that the new treatments will result in benefits. Though many new technologies and treatments do represent true advances, in some cases their marginal improvements are small.