In a clinical trial investigating the efficacy of a new medication for hypertension, 500 participants are randomized to receive either the new medication or placebo. After one year, the incidence of stroke in the treatment group is 10%, while in the control group it is 15%.

Which of the following is the correct calculation of the absolute risk reduction (ARR) associated with the medication?

**A) ARR = 5%**

ARR is calculated by subtracting the risk in the treatment group from the risk in the control group. In this scenario, the risk in the control group (15%) minus the risk in the treatment group (10%) equals an ARR of 5%.

**Answer choice B:** ARR = 10%, is incorrect. To calculate ARR, subtract the risk in the treatment group from the risk in the control group. In this case, 15% (risk in control group) minus 10% (risk in treatment group) equals an ARR of 5%, not 10%.

**Answer choice C:** ARR = 15%, is incorrect.

**Answer choice D:** ARR = 33.3%, is incorrect. This is the relative risk reduction which is (risk in unexposed minus risk in exposed)/risk in unexposed.

**Answer choice E:** ARR = 100%, is incorrect. An ARR of 100% implies that the incidence of the outcome in the treatment group is reduced to zero compared to the control group. While theoretically possible, achieving an absolute risk reduction of 100% is rare in practice and may not be feasible in many clinical settings.

###### Key Learning Point

Absolute risk reduction (ARR) is a measure of the reduction in incidence associated with a treatment. It is calculated by subtracting the risk in the treatment group from the risk in the control group. ARR provides valuable information about the effectiveness of a treatment in reducing the absolute risk of an outcome, such as stroke in this clinical trial. In this scenario, the ARR associated with the new medication for hypertension is 10% compared with 15% in the control group, indicating a 5% absolute risk reduction in the incidence of stroke compared to placebo.