THE SECOND COMMANDMENT
Thou shalt always seek knowledge of the benefits, harms, and costs of treatment, and share this knowledge at all times
Both health professionals and lay people tend to overestimate the benefits of treatments and underestimate their harms. The traditional way to express these is as the number-needed-to-treat (NNT) and the number-needed-to-harm (NNH).
It is important to have a ‘ball-park’ idea of these figures in common clinical situations, but also important to bear in mind their limitations.
First, patients mostly find NNTs and NNHs hard to understand. Second, the numbers do not apply to individuals equally but are just average figures across the populations of clinical trials. Third, people vary widely in how they would balance a given benefit against a given harm.
So we need better ways of a) knowing the true NNT and the NNH in the populations we treat; b) sharing this knowledge with people in ways they can understand; and c) applying this knowledge to the goals and preferences of the individual in front of us.
What is the number needed to treat (NNT)? BMJ 2013