NNT, the crucial health stat you’ve never heard of

Drug companies of course have an incentive to exaggerate a drug’s benefit – there’s lots of money to be made – but in the following article, you learn that public-health authorities tend to tolerate these exaggerations. The reason is because even if there’s only a slight percentage of people who benefit, but millions are on the drug, it may save a few lives. 

Found this article on MSN Slate about a health stat- the NNT – ‘the number needed to treat’ – which is a more objective measure of the benefit of any drug or procedure. If the NNT of a drug is 20 for instance, it means that out of 20 people, only 1 is expected to benefit. Drug companies usually leave this stat out in their promotions. More to follow …

By Darshak Sanghavi
Posted Tuesday, Sept. 26, 2006 on Slate – Medical Examiner

https://www.slate.com/id/2150354/?nav=navoa

Developed by epidemiologists in 1988, the NNT was heralded as a new and objective tool to help patients make informed decisions. It avoids the confusing distinction between “relative” and “absolute” reduction of risk. The NNT is intuitive: To a savvy, healthy person with high cholesterol that didn’t decrease with diet and exercise, a doctor could say, “A statin might help you, or it might not. Out of every 50 people who take them, one avoids getting a heart attack. On the other hand, that means 49 out of 50 people don’t get much benefit.”

But drug companies don’t want people thinking that way; whenever possible, they frame discussions of drugs in terms of relative risk reduction. That’s why the package insert for Pravachol highlights the 31 percent reduction and mentions the NNT not at all. In Pfizer’s 2005 press release promoting the Food and Drug Administration’s approval of Lipitor for patients with diabetes and other risk factors for heart disease, the company said the drug “reduced the relative risk of stroke by 26 percent compared to placebo.” In its 2002 press release promoting an anti-osteoperosis drug, Actonel, Aventis exulted that treated women were “75 percent less likely to experience a first vertebral fracture.” It’s standard for such promotions to make no reference to NNT and to bury information about absolute risks or leave it out entirely.

The reason is simple: Big numbers encourage people, even those who should know better, to prescribe drugs. In 1991, researchers performed a survey of faculty and students in epidemiology at Harvard Medical School—a group that should understand health statistics. When they were presented with identical information about a drug in different formats, almost half had a “stronger inclination to treat patients after reading of the relative change,” or risk reduction, as opposed to the NNT.

When a therapy is extremely effective—like surgery for acute appendicitis or insulin for juvenile diabetes—no one worries about NNTs. But most interventions aren’t home runs, and so NNTs are often the only way to tell if they may be worthwhile, medically and economically. Is your shoulder painful and stiff? The NNT for a cortisone shot is three, which is pretty good, but that also means two out of three patients won’t feel any better after the needles. Does your child have an ear infection? Your pediatrician obliges with a bottle of amoxicillin, but the NNT for antibiotics to shorten the duration of fever is more than 20; thus, at least 19 out of 20 parents force the stuff down their toddlers’ throats for no reason. Is your prostate enlarged? The NNT to avoid surgery is 18 if you take Proscar for four years. The drug costs $100 per month per person, so an insurer spends $86,400 to prevent a single surgery for enlarged prostate. Are you thinking of taking aspirin to help avoid a heart attack? The NNT is a lousy 208. Keep in mind that none of these figures include the risks of side effects.

In some cases, drug companies aren’t the only ones with an incentive to exaggerate a drug’s benefit. Consider statins again. Though an individual person with high cholesterol has little reason to take them (since 49 out of 50 get no benefit), when millions of at-risk people consume the drug, the numbers of averted heart attacks add up. Well-meaning public-health authorities may tolerate the exaggerations of relative risks because they scare people into taking drugs of very slight individual benefit, and if huge numbers of people comply, a few lives may be saved.

These kinds of not-entirely-honest messages about public health aren’t necessarily a problem, even when the NNT for a treatment is very high and thus the likelihood of individual benefit of treatment is very low—that is, as long as the touted intervention is cheap, painless, and accessible. Two examples: wearing a seatbelt and eating a healthy diet. But the calculation is different if we’re talking about an expensive drug. Or something people are supposed to do themselves that’s highly polemical, rife with guilt, and sometimes extremely stressful. Like breast-feeding.

In June, the New York Times ran an article headlined, “Breast-Feed or Else.” It suggested that experts believe that “breast-fed babies are at lower risk for sudden infant death syndrome and serious chronic diseases later in life, including asthma, diabetes, leukemia and some forms of lymphoma.” Yet, the article never mentions the NNT for breast-feeding to prevent these scary diseases. Neither does any general-interest press article in LexisNexis, a database. There’s a reason for this omission: The NNTs are astronomically high. Reasonable women might think that breast-feeding isn’t worth the trouble—a conclusion that you don’t want drawn if you’re promoting breast-feeding at any cost.

In the end, the excuse that it’s OK to promote largely ineffective drugs and interventions for the sake of the greater good doesn’t really wash. Nor does the excuse that NNTs are difficult to understand conceptually or that the math is too hard. Patients look to doctors to translate and interpret complex, often-conflicting information from drug companies, medical journals, and the media. NNTs are a tool for doing that. Doctors must keep faith that patients can get it together to understand their choices. If we make their use standard, patients and public discussion will follow suit.