Epidemiology & Public Health
Intermediate

Number Needed to Treat

Number of patients who must receive a treatment for one additional patient to benefit.

Formula

NNT=1ARRNNT = \frac{1}{ARR}

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Variables

NNTNumber needed to treat
ARRAbsolute risk reduction (control rate − treatment rate)

Example

Control event rate 20 %, treatment 15 % → ARR = 0.05, NNT = 20

Did You Know?

An NNT of 1 would be a perfect cure. In practice, aspirin for heart-attack prevention has an NNT around 100.

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