Number Needed To Treat
- NNT quantifies how many patients must receive a treatment to produce one additional desired outcome.
- A lower NNT indicates greater practical effectiveness for the specified outcome.
- NNT is study-dependent and should be interpreted alongside cost, side effects, and other risk measures.
Definition
Section titled “Definition”Number needed to treat (NNT) is defined as the number of patients who need to receive a treatment in order to achieve a specific benefit or outcome.
Explanation
Section titled “Explanation”NNT is a statistical measure used to quantify treatment effectiveness for a predefined outcome. It is calculated from the results of a particular study and describes how many treated patients are required to realize one additional positive outcome compared with a control. Because NNT is derived from study data, it can vary with factors such as condition severity, treatment duration, and baseline risk in the population studied.
Examples
Section titled “Examples”General interpretation
Section titled “General interpretation”If a treatment has an NNT of 10, this means that 10 patients need to receive the treatment in order to achieve 1 additional positive outcome (such as a reduced risk of heart attack).
Cholesterol-lowering medications
Section titled “Cholesterol-lowering medications”If a study finds that 10 patients need to receive the cholesterol-lowering medication in order to prevent one additional heart attack, and 50 patients receive the medication in the study, the NNT for the medication would be 5 (50 patients / 10 heart attacks prevented).
Vaccines
Section titled “Vaccines”If a study finds that 100 individuals need to receive a vaccine in order to prevent one additional case of influenza, and 500 individuals receive the vaccine in the study, the NNT for the vaccine would be 5 (500 individuals / 100 cases prevented).
Use cases
Section titled “Use cases”- Evaluating the effectiveness of cholesterol-lowering medications.
- Assessing vaccine effectiveness in preventing cases of infectious disease.
Notes or pitfalls
Section titled “Notes or pitfalls”- NNT is study-specific and may not generalize to a broader population.
- NNT can be affected by the severity of the condition, length of treatment, and the population’s baseline risk.
- Context matters: a low NNT does not alone determine whether a treatment is preferable; cost, side effects, and availability also influence decisions.
- NNT should be considered alongside other measures such as relative risk reduction (RRR) and absolute risk reduction (ARR).
Related terms
Section titled “Related terms”- Relative risk reduction (RRR)
- Absolute risk reduction (ARR)