Public health researchers are analyzing data from a recent prospective cohort study investigating the adverse effects of a new oral synthetic retinoid used for severe nodular acne. The study followed patients taking the new retinoid and patients taking standard topical therapies for one year. During the study period, patients in the new retinoid group developed significantly elevated liver transaminases. In the standard therapy group, patients developed similar transaminase elevations. Based on these findings, what is the number needed to harm (NNH) for the new oral synthetic retinoid compared to standard therapy?
Answer: 10
Answer
10
The Number Needed to Harm (NNH) represents the number of patients who must be exposed to a risk factor (or treatment) over a specific period to cause one additional adverse outcome. It is calculated as the inverse of the Absolute Risk Increase (ARI), which is also known as the Attributable Risk. First, the incidence of the adverse event in the exposed group is . Next, the incidence in the unexposed group is . The ARI is the difference between these two incidences: (or ). The NNH is calculated as , which is . Therefore, patients need to be treated with the new retinoid instead of standard therapy to cause one additional case of elevated liver transaminases.
Step-by-Step Solution
Key Concept
Number Needed to Harm (NNH) is calculated as the inverse of the Absolute Risk Increase (ARI) between an exposed and an unexposed group.