Number needed to treat
An EBM term - 'Number Needed to Treat to produce benefit in one.
An effective intervention well-targeted at a clearly defined group should have a low NNT.
Interventions with a high NNT may nevertheless be worth considering and trying. The one who gets the benefit gets the benefit despite however many do not. In that situation, and particularly if there is a big placebo effect or the effect is difficult to determine, the n-of-1 trial is worth considering.
The companion term to NNT is NNH - the Number Needed (to treat) to Harm one patient.