From the Guidelines
A high patient-to-treat (number-to-treat) ratio is generally considered to be greater than 100, as it indicates that a large number of patients need to be treated to achieve one additional good outcome. When evaluating the effectiveness of a treatment, the number needed to treat (NNT) is a crucial metric, as it represents the number of patients who need to be treated to achieve one additional good outcome 1. According to the study published in the Annals of Emergency Medicine in 2011, the NNT is calculated as 1/absolute risk reduction, where absolute risk reduction is the risk difference between two event rates (i.e., experimental and control groups) 1. The study provides a framework for interpreting likelihood ratios and NNT, highlighting that an NNT of 100 or higher is generally considered high, as it indicates a small absolute risk reduction and a low likelihood of achieving a good outcome 1. Some key points to consider when evaluating NNT include:
- NNT is inversely related to absolute risk reduction, meaning that a higher NNT indicates a smaller absolute risk reduction
- An NNT of 100 or higher is generally considered high, as it indicates that a large number of patients need to be treated to achieve one additional good outcome
- The interpretation of NNT depends on the context and the specific treatment being evaluated, as well as the potential benefits and harms of the treatment 1. In clinical practice, a high NNT should prompt clinicians to carefully weigh the potential benefits and harms of a treatment and to consider alternative therapies that may be more effective or have a more favorable risk-benefit profile 1.
From the Research
Definition of Number Needed to Treat (NNT)
- The Number Needed to Treat (NNT) is a measure of the effectiveness of a treatment, representing the number of patients who must be treated to prevent one adverse outcome or to achieve one beneficial outcome 2, 3, 4.
- It is calculated as the reciprocal of the risk difference between the treatment and control groups 5.
Factors Affecting NNT
- The NNT depends on the baseline risk of the population, with higher baseline risks resulting in lower NNTs 3.
- The NNT also depends on the specific treatment or intervention being used, as well as the population being studied 6.
Interpretation of NNT
- A lower NNT indicates a more effective treatment, as fewer patients need to be treated to achieve a beneficial outcome 5.
- For example, an NNT of 2 indicates that 2 patients need to be treated to prevent one death, whereas an NNT of 15 indicates that 15 patients need to be treated to prevent one stroke or death 5.
High Patient-to-Treat Ratio
- A high patient-to-treat ratio, or high NNT, indicates that many patients need to be treated to achieve one beneficial outcome.
- This can be seen in treatments with low efficacy or in populations with low baseline risks 3, 5.
- For instance, a treatment with an NNT of 15 has a higher patient-to-treat ratio compared to a treatment with an NNT of 2 5.