One of the greatest concepts I have run across since I finished school is the Number Needed to Treat (abbreviated NNT). NNT was never taught back when I went to medical school (we had barely given up The Four Humors!). Instead, we were taught “the p-value.” Does anyone else remember the p-value? The p-value of a study, it turns out, is a relatively poor measure of study validity, partly because it implies an “all-or-nothing” kind of understanding of studies: either the study is “valid” (meaning a p-value of >95%) or it is not. Either the treatment being studied works or it does not. And if a treatment works, it must work for all people.
Of course, in real life, this is not the case. No drug is universally good or bad. All drugs help some people, harm some people (with adverse side effects) and make no difference one way or another in some people. These numbers can be derived from any study’s data. There is even a fabulous website devoted to this where you can look up the NNT and its corollary, the Number Needed to Harm (NNH) for all sorts of drugs and treatments (found here).
Since it is influenza season and time for us to get our flu shots (I got mine yesterday), I thought it would be a great time to see how beneficial the flu vaccine is. What is the NNT for the flu vaccine? And while we are at it, why don’t we also look at the data on oseltamivir (Tamiflu) while we’re at it?
Influenza Ward, Great Pandemic 1919
