Do you know about the number needed to treat?

The world of medical stats is just as confusing – and seductive – as political stats. The raw value of a stat is often left out of the equation.

For example, a study of 1,000 people finds that 6 people get a particular cancer and 4 of them die. Taking drug A as opposed to old drug B reduces that number from 4 to 3. 1/6 = roughly 16%. Since 15% is the benchmark of statistical significance in science (and many disciplines), the study can promote the finding that deaths are significantly reduced with new drug A. Never mind that the news is irrelevant for 994 study participants and in real numbers, we’re talking about one person.

I believe even one person is certainly worth saving, but I use this example to highlight a very real problem with statistics. It’s all in your perspective, and when you view new drugs from a less popular statistic – the number needed to treat, or NNT – the picture sometimes changes.

To use a real-world example I recently read in Time magazine, let’s look at statins. Statins have become a commonplace Rx for the post-40 crowd, and they’re especially popular for men. (By the way, this gender skewing is something I have a problem with, as just as many women have cardiovascular health issues and 1 in 3 women – period – die from heart disease.)

Statins are used to reduce bad cholesterol, in the hopes that heart disease and subsequent heart attacks will be prevented. We’ve all seen the “30% reduced risk” in statin ads. But this isn’t 30% across the board – although that’s the perception and that’s why everyone’s on statins. Enter NNT.

This 30% number is the number of people in one of the study’s control groups (there’s a statin-taking group and a placebo-taking group). Moreover, this is 30% in real numbers – meaning, of men who would have had the heart attacks anyway (a very small number), that number was reduced by 30%. It’s not a 30% reduction in total.

But millions of men are taking statins. To prevent one heart attack, thousands of men who likely wouldn’t have a heart attack are taking statins. This is the number needed to treat. According to Time, 50 people have to take this drug to stop one heart attack (which, as Time points out, is not likely to be fatal). That’s 50 people needlessly popping a daily pill with untold side effects. Now, of those 50 people taking a drug to stop one heart attack that probably won’t be fatal, I wonder how many face serious, expensive and possibly life-threatening health problems.

Of course, on the scale of the total population, 50:1 becomes many thousands of heart attacks prevented – but many hundreds of thousands facing unnecessary and dangerous side effects (and spending a lot of extra cash).

That’s NNT, and that’s the true measure of a drug’s effectiveness and value.

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[tags]statistics, cancer, statins, cholesterol, heart disease, heart attack, NNT, number needed to treat[/tags]

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