What does the number needed to treat (NNT) define?

The number needed to treat (NNT) is a measure used in healthcare to indicate how many patients must be treated with a specific intervention to prevent one additional adverse event or achieve one additional desired outcome, such as recovery or clinical improvement. This statistic is particularly useful in comparing the effectiveness of different treatments and in assessing their overall benefit to patients.

For instance, if an NNT of 5 is calculated for a certain drug regarding stroke prevention, this means that five patients would need to be treated with that drug to prevent one stroke from occurring. The lower the NNT, the more effective the treatment is considered to be, as fewer patients need to be treated to achieve the desired healthcare outcome.

In contrast, the other options do not accurately represent the definition of NNT. The percentage of patients who respond to treatment focuses on the response rate rather than the number needed to prevent an outcome. The total number of side effects from treatment would be more related to safety profiles and adverse effects rather than efficacy measured by NNT. Lastly, the duration of treatment required for efficacy pertains to the length of time a treatment is administered, not the quantification of patient outcomes as expressed by NNT.