Number Needed To Treat – Epidemiology – Video Lecture

Number Needed To Treat:

The number needed to treat (NNT) is an epidemiological measure used in assessing the effectiveness of a health care intervention, typically a treatment with medication. The number needed to treat is the average number of patients who need to be treated to prevent one additional bad outcome (i.e. the number of patients that need to be treated for one to benefit compared with a control in a clinical trial). It is defined as the inverse of the absolute risk reduction. It was described in 1988. The ideal NNT is 1, where everyone improves with treatment and no one improves with control. The higher the NNT, the less effective is the treatment.


This video on Number Needed To Treat has been provided by: Terry Shaneyfelt

Significance of Number Needed To Treat:
The NNT is an important measure in pharmacoeconomics. If a clinical endpoint is devastating enough (e.g. death, heart attack), drugs with a high NNT may still be indicated in particular situations. If the endpoint is minor, health insurers may decline to reimburse drugs with a high NNT. NNT is significant to consider when comparing possible side effects of a medication against its benefits. For medications with a high NNT, even a small incidence of adverse effects may outweigh the benefits. Even though NNT is an important measure in a clinical trial, it is infrequently included in medical journal articles reporting the results of clinical trials. There are several important problems with the NNT, involving bias and lack of reliable confidence intervals, as well as difficulties in excluding the possibility of no difference between two treatments or groups.

How to calculate Number Needed To Treat:
To calculate the NNT, you need to know the Absolute Risk Reduction (ARR); the NNT is the inverse of the ARR:


  • Where ARR = CER (Control Event Rate) – EER (Experimental Event Rate).
  • NNTs are always rounded up to the nearest whole number.




References for Number Needed To Treat:

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