In the Tuesday, 6 November 2007 edition of the Wall Street Journal, Pfizer took out a full-page ad encouraging people to “Ask your doctor” about Lipitor, a drug which claims to lower your “risk” of a heart attack (p. A13). In enormous bold print are the words:
Lipitor reduces risk of heart attack by 36%*.
Following that asterisk on the 36% leads to something interesting:
*That means in a large clinical study, 3% of patients taking a sugar pill or placebo had a heart attack compared to 2% of patients taking Lipitor.
Congratulations, Pfizer! This ad scores a solid 7 on the Statistical Deception Scale.
First, if you take Lipitor your risk is only lowered by a relative amount, from an already low 2% to a slightly lower 1%. Your real risk is only lowered by 1%. There is a world of difference between that 36% and 1%, and the ad did say, sort of, that the risk was relatively lowered, not lowered absolutely, so it wasn’t terribly deceptive at that point. It’s true, too, that some people might think to themselves, “Ah, any lowering is good, even if it’s only 1%.” More on that sentiment in a moment.
But what most people won’t see, or will ignore, are the smaller words under the bold headline, which say that your risk is lowered “If you have risk factors such as family history, high blood pressure, age, low HDL (‘good’ cholesterol) or smoking.” Aha! This is what ups Pfizer’s ranking on the deception scale.
Thus, in order to get the 1% reduction it turns out that you have to be in a pretty high risk group to begin with; namely, those with “multiple” risk factors. How many risk factors do you have to have before you can hope for the reduction? Two? Three? The ad doesn’t say. Maybe you need all five before you can hope for the reduction. That is the most likely reading of the ad.
What if you don’t have all five? We might guess that your absolute risk reduction is either zero or negligible. We guess this because if people could reduce their risk generally, without belonging to a highly selective group, that Pfizer would have boasted of this. They did not so boast, so etc. etc.
Back to the “any lowering is good” sentiment. On the page opposite the pictures, Pfizer has quite a long list called “POSSIBLE SIDE EFFECTS OF LIPITOR”. Among these new risks are, muscle problems, kidney “problems” or even failure, liver problems, nausea, vomiting, brown colored urine, tiredness, yellowing eyes (!), rash, gas, and others. The key words are these:
Fewer than 3 people out of 100 stopped taking LIPITOR because of side effects.
Well, must I point out that 3 out of 100 is 3%, which is more—67% more!—than the 2% (in the high risk group) who will have a heart attack, and 200% more than the 1% (or so) of the “regular” people who will have a heart attack? I guess I don’t need to. Of course, we can’t figure out, given only the data that Pfizer provides in the ad, what the actual chance is that a regular person will have a heart attack or suffer “side” effects. But there is enough information provided that should severely limit enthusiasm for this drug.
The advertisement also pictures Robert Jarvik, inventor of the “Jarvik artificial heart”, badly in need of a haircut, standing in front of a colorful heart-like object. But he is a celebrity doctor, and isn’t that all you really need to know?