Abbreviated to NNT or NNTT, this is a simple statistical concept, relevant to clinical practice in medicine. It is the number of people you need to treat in order to gain some specified benefit. This number is quoted with reference to who you're treating, what the treatment is, the outcome of interest, and a time scale. Examples of commonly quoted NNT's are:

• Current wisdom is that you need to treat 78 people who have never had a heart attack with statins for 5 years in order to prevent one Myocardial Infarction.
• You need to treat 30 people who have ischaemic heart disease with statins for 5.4 years in order to prevent one death (see the Scandinavian Simvastatin Survival Study)
• You need to treat 43 elderly hypertensive people for 4.5 years to prevent one stroke.
• You need to give aspirin to 40 people with acute Myocardial Infarction in order to prevent one death.

This number is good for working out whether it's worth trying some treatment, it helps you and your doctor do a cost/benefit analysis.