If you don’t have high cholesterol, but you do have a high level of inflammation in your blood, you are about to be targeted by a new marketing campaign for Crestor, the statin drug. You will be told the drug can lower heart attack risk by as much as 50 percent. Should you swallow this advice, and should you take a daily dose of these pills for the rest of your life?
The downside of statin pills is the possibility that they increase risk of diabetes and liver damage. The upside, of course, is reducing your risk of dying from the nation’s No. 1 killer, heart disease. So it’s important to know accurate numbers to make an intelligent decision.
The 50% reduction in heart attack is actually a statistical sleight of hand. The correct risk reduction number is actually around one in 500, or 0.2%. To understand the number manipulation involved, read on for a gentle short course in medical statistics.
These numbers come from a big study that the FDA used to give the green light to Crestor’s new marketing campaign. The researchers found that around four in 1,000 patients with a high level of C-Reactive Protein (an inflammation marker in the blood) but with normal cholesterol had heart attacks if they took a dummy (placebo) pill in the study. Similar patients who took Crestor had a heart attack rate of around two in 1,000. These numbers come from the tail end of a new article in the New York Times on the FDA’s approval of the new Crestor campaign.
Now the difference between four and two is 50 percent, but that conveniently leaves out the denominator in the statistic. The real risk reduction is from four in 1,000 to two in 1,000, or a difference of two in 1,000, which is the same as 0.2 percent. The 50 percent number is called the relative risk, and the 0.2 percent number is the absolute risk. Absolute risk is what measures real people and is the one we should focus on, but marketers like relative risk because it produces more dramatic numbers. Put another way, you can have statistically significant benefits from taking a drug on paper, but the clinically significant benefit, in real life, is much much smaller.
In my book, The Life You Save: Nine Steps to Finding the Best Medical Care — and Avoiding the Worst, I discuss the Crestor story because it’s just one example of how consumers can be misled by medical numbers. There’s a straightforward solution, which I call “counting the people,” when you are looking at any supposed medical breakthrough. Here’s what I said in the book:
The real number [of how many patients benefit from a drug] might be enough to persuade some patients to take the drug. But it’s a lot different than fifty percent. Bottom line: to make intelligent choices about treatments, patients need to understand how many patients like them are really expected to benefit from the treatment. You can get these answers by focusing on how many actual people are helped by the treatment. Do not focus on misleading vague numbers like “50 percent improvement.” Fifty percent of what? Focusing on real numbers of real people will give you the answer.
As a patient safety advocate, I want all smart consumers of health care to know at least a little bit about statistics — because the real numbers can be very eye-opening.