Number Needed to Treat Calculator

The Number Needed to Treat (NNT) calculator helps determine how many patients need to be treated to prevent one additional adverse event. This is an important measure in clinical trial analysis and evidence-based medicine.

Input Parameters

Calculation Results

Calculation Formula

NNT = 1 / (AR_Treatment - AR_Control)

Where:
NNT = Number Needed to Treat
AR_Treatment = Absolute Risk in Treatment Group
AR_Control = Absolute Risk in Control Group

Number Needed to Treat Calculator Usage Guide

Learn how to use the Number Needed to Treat Calculator and interpret its results

How to Use This Calculator

  1. Enter the Absolute Risk in the Control Group (the risk of the adverse event in the group receiving no treatment)
  2. Enter the Absolute Risk in the Treatment Group (the risk of the adverse event in the group receiving the treatment)
  3. Click the Calculate button
  4. The calculator will display the Number Needed to Treat (NNT) and its 95% confidence interval

Interpreting the Results

  • NNT: This indicates how many patients need to be treated to prevent one additional adverse event. A lower NNT suggests a more effective treatment.
  • Confidence Interval: This provides a range within which the true NNT likely falls (with 95% confidence).
  • Example Interpretation: If the NNT is 10 with a 95% CI of 7-15, it means that treating 10 patients will prevent one adverse event, and we are 95% confident that the true NNT lies between 7 and 15 patients.

Principles of NNT Calculation

The NNT is calculated as the reciprocal of the absolute risk reduction (ARR), where ARR = AR_Treatment - AR_Control. The formula is straightforward but requires accurate input data. Remember that NNT is most meaningful when the intervention is relatively safe, as a high NNT might not justify the treatment if the side effects are severe.

Limitations

This calculator provides a simplified calculation. In practice, adjustments for baseline risk, adherence, and other factors may be needed. The confidence interval calculation here uses a simplified formula; more complex methods may be used in formal clinical research.