Number needed to treat

Number Needed to Treat (NNT) is a statistical concept used in epidemiology and evidence-based medicine to measure the effectiveness of a health intervention. The NNT is the average number of patients who need to be treated to prevent one additional bad outcome or produce one additional good outcome. It is a way of communicating the benefits of a treatment in a meaningful way.

Definition

The Number Needed to Treat is defined as the inverse of the absolute risk reduction (ARR). The ARR is the difference in risk between the control group and the treatment group in a randomized controlled trial. The NNT is calculated as 1/ARR.

Interpretation

The NNT provides a measure of the impact of a treatment or intervention. A lower NNT means that fewer people need to be treated for one person to benefit. Conversely, a higher NNT means that more people need to be treated for one person to benefit. The NNT can be used to compare the effectiveness of different treatments.

Limitations

While the NNT is a useful measure, it has some limitations. It does not take into account the severity of the outcome that is being prevented or the side effects of the treatment. It also assumes that the treatment effect is the same for all individuals, which may not be the case.

Examples

For example, if a drug has an NNT of 5, it means that 5 people need to be treated with the drug for one person to benefit. If a surgical procedure has an NNT of 20, it means that 20 people need to undergo the procedure for one person to benefit.

See also

• Number needed to harm
• Relative risk reduction
• Odds ratio
• Risk ratio