Math clogs people’s brains

One of the most common drugs people have is Atorvastatin known more popularly as Lipitor:


I can’t speak for everyone else, but when I see a number like that it makes me think that you can prevent a heart attack in more than 1 out of 3 people. But four years ago, Businessweek pointed out the details of the fine print below the glaring asterisk of the 36% number.

“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”

What that boils down to is maybe one fewer heart attack per 100 people. What wasn’t covered in the article was how such a huge number came to be. That 36% is a real number and this is how its done.

In statistics it’s known as relative risk and compares the ratio of heart attacks between both groups. I’ll just use the 2 and 3 percent numbers they provided instead of looking up the actual study. That breaks down to:

Lipitor: 2 heart attacks per 98
Sugar Pill: 3 heart attacks per 97

So the odds of heart attack for the Lipitor group is 2:98 which is 0.02041 and the odds of heart attack on sugar pill is 3:97 which is 0.03093. Next, you take these two numbers and you do (odds with Lipitor)/(odds with sugar pill) which is (0.02041)/(0.03093). This comes out to 0.66 which means the odds of a heart attack on Lipitor is 66% to the odds of having one with a sugar pill. You then subtract 1.00 from the percent: 1.00-0.66 and you get 34% lower. The reason it is not 36% exactly is because the 2 and 3 percent numbers used were probably rounded.

The confusion comes because we don’t often think in terms of relative risks but absolute risk instead. Was that Ad portraying the 36% as a relative risk instead of an absolute risk? Hmm, that depends on the reader but I definitely thought it was absolute risk when I first saw it.

BTW if sugar really is the culprit behind heart disease and not fat….maybe they shouldn’t be giving sugar pills to control groups in these sort of studies!


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