This learning resource is linked to the ARR and NNT / NNH Calculator.
Use the ARR and NNT / NNH Calculator
Why Calculation Errors Occur
Use comparable adverse-event risks over the same follow-up period. NNT/NNH is rounded up; no confidence intervals or treatment recommendation. Most calculation failures are caused by incorrect inputs, inconsistent units, an unsuitable formula, transcription errors, or incorrect interpretation rather than by arithmetic alone.
Common Mistakes
- Mixing units: Values are entered in different unit systems without conversion.
- Incorrect percentage format: A value expected as 5 is entered as 0.05, or the reverse.
- Using rounded source data: Intermediate values are rounded too early.
- Wrong parameter selection: A similarly named value is used in place of the required input.
- Ignoring assumptions: The selected method is used without confirming that its conditions apply.
- Missing independent review: A result is copied directly into a GMP record without verification.
How to Prevent Errors
- Use verified source data.
- Write down the units beside every input.
- Confirm the formula against the approved procedure.
- Retain sufficient decimal places during intermediate steps.
- Review the final result for scientific reasonableness.
- Record assumptions and obtain approval where required.
Before Final Use
Check the result against the example, historical data, specification, protocol, or a second calculation method whenever practical.