NNT Calculator
Number needed to treat.
NNT = 1 ÷ absolute risk reduction. How many to treat for one benefit.
How the Math Works
The Number Needed to Treat (NNT) is calculated by taking the reciprocal of the absolute risk reduction (ARR). First, determine the treatment event rate (TER) in the treated group and the control event rate (CER) in the untreated group. Subtract CER from TER to get ARR (ARR = CER - TER). Then divide 1 by the ARR: NNT = 1 / ARR. A smaller NNT indicates a more effective treatment, meaning fewer patients need to be treated to prevent one adverse outcome.
Practical Applications
To apply the NNT calculation, researchers conduct clinical trials comparing a treatment group to a control group. After determining the event rates in both groups, apply the formula to quantify how many patients need treatment for one to benefit. Healthcare professionals use this metric to weigh treatment effectiveness against costs, side effects, and patient preferences when making clinical decisions or advising patients on treatment options.
Day-to-Day Use
In everyday life, understanding NNT helps patients make informed decisions about their health. When a doctor recommends a medication, knowing the NNT lets you understand how many people like you would need to take the drug for one person to benefit. This empowers you to ask meaningful questions about treatment risks and benefits, helping you weigh whether the potential benefits justify the time, cost, and potential side effects for your specific situation.
FAQ
Ideal NNT?
Lower is better — ideally close to 1.