A randomized controlled trial is conducted to evaluate a new selective estrogen receptor modulator (SERM) for the prevention of breast cancer in high-risk postmenopausal women. The study enrolls 1,600 women, who are randomly assigned in a 1:1 ratio to receive either the new SERM or a placebo. The participants are followed for 5 years. During the follow-up period, 56 out of the 800 women receiving the new SERM develop deep vein thrombosis (DVT). In the placebo group, 16 out of the 800 women develop DVT.
Based on these study results, what is the number needed to harm (NNH) for DVT associated with this new SERM?
Answer: 20
Answer
20
The number needed to harm (NNH) is an epidemiological measure that indicates how many patients need to be exposed to a risk factor (in this case, the new SERM) over a specific period to cause harm in one patient that would not otherwise have been harmed. It is calculated as the inverse of the Absolute Risk Increase (ARI). First, the incidence of the adverse event in the exposed group is . The incidence in the unexposed (placebo) group is . The ARI is the difference between these two incidences: . The NNH is calculated as , which is . Therefore, 20 patients must be treated with the new SERM for 5 years to result in one additional case of deep vein thrombosis compared to placebo.
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Number Needed to Harm (NNH)