This learning resource is linked to the ARR and NNT / NNH Calculator.
Use the ARR and NNT / NNH Calculator
Calculation Objective
Use comparable adverse-event risks over the same follow-up period. NNT/NNH is rounded up; no confidence intervals or treatment recommendation.
Formula
ARR = control adverse-event risk − treatment risk; NNT = 1/ARR (fraction); NNH = 1/abs(ARR) when ARR < 0
Input Variables and Units
| Input | Field Type | Unit |
|---|---|---|
| Control adverse-event risk (%) | Number | As specified |
| Treatment adverse-event risk (%) | Number | As specified |
| Shared follow-up period (e.g. 12 months) | Text | As specified |
Example Inputs
control=20, treatment=10, followup=12 months
Example Result
ARR=10 percentage points; NNT=10 over 12 months
How to Reproduce the Example
- Match each example value to the input variable and confirm units.
- Substitute those values into the displayed formula.
- Perform the arithmetic with appropriate intermediate precision.
- Compare the result with the recorded example output and the interactive calculator.
Assumptions and Interpretation
Check the formula scope, input basis, unit conversions and rounding against the source method. The stored example is not an independent verification of the calculator.