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Computes the Number Needed to Treat (NNT), a standard evidence-based medicine statistic used to interpret clinical trial results: Absolute Risk Reduction (ARR) = control event rate - treatment event rate, and NNT = 1 / ARR. If the treatment rate is higher than the control rate, the standard convention reports a Number Needed to Harm (NNH) instead. Pure arithmetic given the two rates. For general reference and educational (statistics/EBM) purposes only — not a specific treatment recommendation.
How it works
Enter the control group event rate and the treatment group event rate as percentages. The tool computes the absolute risk reduction and its reciprocal.
- Enter control group event rate (%).
- Enter treatment group event rate (%).
- Click Calculate to see your results.
Examples
Control 20%, Treatment 10%
ARR = 20% - 10% = 10%. NNT = 1/0.10 = 10 — on average, 10 patients need to receive the treatment to prevent one additional event.
Who should use it
- Evidence-based medicine education.
- Interpreting clinical trial results.
Industry applications
- Clinical education
- Evidence-based medicine teaching
Advantages
- Standard, widely-taught EBM statistic.
- Automatically reports NNH when the treatment rate is worse than control.
Limitations
- Does not account for confidence intervals around the underlying rates.
- Not a substitute for full trial-result interpretation.
Common mistakes to avoid
- Comparing NNTs across different studies or conditions without considering baseline risk, time horizon, and outcome severity, which all affect what counts as a "good" NNT.
Best practices
- Always pair NNT with the Number Needed to Harm (NNH) for the treatment's side effects when making a full risk-benefit judgment, per standard EBM teaching.
Tips
- NNT is most meaningful when reported alongside its confidence interval and the study's follow-up duration, per standard EBM practice.