During a morning report session, an internal medicine resident evaluates a manufacturer-sponsored slide deck for a newly approved migraine prophylactic medication. The featured slide contains a bar graph summarizing the primary outcome: the proportion of patients completely free of migraines at months. The data indicate that of the patients taking the new medication achieved migraine freedom, whereas of the placebo group achieved the same endpoint. The slide prominently highlights a " relative increase in migraine freedom" for the treatment group. Based on these results, how many patients need to receive the new medication instead of the placebo to result in one additional patient achieving migraine freedom at months?
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Answer
The Number Needed to Treat (NNT) is .
To find the number of patients that must be treated to achieve one additional positive outcome, the Number Needed to Treat (NNT) must be calculated. The first step is to calculate the Absolute Risk Reduction (ARR), which is the absolute difference in outcome rates between the experimental and control groups. Here, the treatment rate is and the placebo rate is . Thus, , or . The NNT is the inverse of the ARR: . Therefore, patients must be treated with the new medication instead of a placebo to achieve one additional instance of migraine freedom.
Step-by-Step Solution
Key Concept
Calculating Number Needed to Treat (NNT) from absolute risk differences in medical literature