# Relative and Absolute Risk

I have been reading a fascinating book on data in the medical world and how it is doctored. Doctoring Data by Malcolm Kendrik, in case anyone wants to read it.

One of the concepts he introduced to me was the concept of absolute and relative risk. Both of these concepts are vital to our understanding of the efficacy of a drug.

Absoulute risk measures the actual difference a medicine makes to people. Relative risk measures the difference it makes as compared to another group. The difference is vital.

So let us take two groups of, say, 1000 people. Let us say both have a risk of 2/1000 dying of a particular disease, or 0.2%. Now assume a drug comes along claiming that it can reduce risk.

Wonderful; bring it on, we would say.

But you might want to ask how much risk would be reduced. Would the reduction be worth it?

The drug manufacturer would like to say that we reduced the relative risk by 50%. Excitedly, we would want to sign up in droves. Except there is a catch.

When asked about absolute risk reduction, they would ruefully say 0.1%.

0.1%? But didn't you say there would be a reduction of 50%?

Yes, that is where statictics come into play. The actual numbers are 2/1000 prior to the medicine and 1/1000 after the medication.

So yes, technically speaking, there was a 50% reduction in the relative risk, but only 1 less person per thousand in absolute terms. That is the power of statistics and how you use them.

If you were that one person, of course, you would be delighted.

But what about the 998 people who took the medicine thinking they would benefit, seduced by the claim of a 50% reduction, only to find out it made no difference at all?

It is not my argument that you should not medicate yourself if you are at risk. Just that, you should be aware of what you are doing and the benefits you would get.

PS: Since the concept has been taken from the book, naturally, the contents would sound similar to the original book.

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