What is a “number needed to treat?”
Number needed to treat is a statistic calculated by epidemiologists (I am an epidemiologist by training) to determine how effective something is.
I was going to put the derivation and the formula here, but I decided that linking to Wikipedia was easier.
The real power of number needed to treat is in how easy it is to understand. Let’s say that you do a study with Drug A and do all the statistics and find out that the number needed to treat is 3. That means that to avoid getting Disease X, you have to give Drug A to 3 people. Let’s say you do another study with Drug B and find out the number needed to treat is 100 (meaning you have to treat 100 people for the drug to work in 1 of them). Which drug is more effective?
Well, if I want one person to get better, I have to give Drug A to 3 people or Drug B to 100 people.
To put it another way, if I gave Drug A to 100 people, 33 would get better. If I gave Drug B to 100 people, only 1 would get better.
Man, maybe number needed to treat isn’t that easy to understand…