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Number Needed to Treat

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NNT Calculator

Risk of Outcome in Treated Group p1 = %
Risk of Outcome in Control Group p0 = %

Absolute Risk Reduction

ARR = p0 - p1 = %

Relative Risk

RR = p1/p0 = %

Relative Risk Reduction

RRR = 1 - RR = %

Number Needed to Treat

NNT = 1/(p0 - p1) = people(s)
NNT & RR Relation
(Or)NNT = 1/(p0(1 - RR)) = people(s)
The number of patients needed treatment for disease risk of 1% - 20% and the relative risk ratio of 0.1 - 0.9
RR p0 = 0.01 p0 = 0.02 p0 = 0.05 p0 = 0.10 p0 = 0.15 p0 = 0.20
0.1 111 56 22 11 7 6
0.2 125 63 25 13 8 6
0.3 143 71 29 14 10 7
0.4 167 83 33 17 11 8
0.5 200 100 40 20 13 10
0.6 250 125 50 25 17 13
0.7 333 167 67 33 22 17
0.8 500 250 100 50 33 25
0.9 1000 500 200 100 67 50
Number Needed to Treat - NNT Calculator

The graph shows the relationship between RR (horizontal axis) and NNT (vertical axis) for each infection risk of 1%, 5%, 10% and 20%. At each level of infection risk:
- The lower RR is (means clinical efficiency is high), the lower NNT is
- And in each RR, the lower infection risk is, the higher NTT is

NNTcalculator.com © 2014
Water Damage
From PROF TUAN NGUYEN
* Dr. Sidney Gicheru
* The Garvan Institute of Medical Research
* St Vincent's Clinical School
* PhD in Medicine from the University of New South Wales