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Calculate the impact of a medical intervention by determining how many patients need to be treated to prevent one additional adverse outcome.
Enter the number of events and total patients for each group.
Calculated risk metrics and NNT
Enter event data to view NNT statistics.
The Number Needed to Treat (NNT) is an epidemiological measure used to communicate the effectiveness of a health-care intervention. It is defined as the number of patients who need to be treated for one of them to benefit compared with a control in a clinical trial.
Control Event Rate (CER) = Control Events / Control Total
Experimental Event Rate (EER) = Experimental Events / Experimental Total
Absolute Risk Reduction (ARR) = | CER - EER |
Number Needed to Treat (NNT) = 1 / ARR
Note: NNT is always rounded up to the nearest whole number.
If the Experimental Event Rate is higher than the Control Event Rate (e.g., side effects or adverse outcomes are more common in the treatment group), the calculation yields the Number Needed to Harm (NNH). This indicates how many patients need to be exposed to the risk factor to cause one additional person to be harmed.
Disclaimer: This tool is intended for educational and reference purposes only. It should not be used as a substitute for professional medical judgment or advice.