American Board of Internal Medicine (ABIM) Certification Practice Exam

How is the Absolute Risk Reduction (ARR) calculated?

1. The difference in treatment outcomes between two groups

2. The rate of complications in the treatment group

3. The percentage of patients who improved in the control group

4. The average treatment outcome in each group

The correct answer is: The difference in treatment outcomes between two groups

Absolute Risk Reduction (ARR) is calculated by determining the difference in the rates of an outcome between two groups, typically a treatment group and a control group. This measurement provides a straightforward way to understand how much the treatment reduces the risk of the negative outcome compared to not receiving the treatment. In practical terms, ARR can be expressed using the formula: ARR = (Event Rate in Control Group) - (Event Rate in Treatment Group) This calculation focuses purely on the actual difference in risk between the two groups, allowing clinicians to appreciate the tangible benefit of the intervention being studied. For example, if the event rate (e.g., disease occurrence) in the control group is 10% and in the treatment group is 5%, the ARR would be 5%. This means there is a 5% reduction in risk of the event occurring due to the treatment, offering clear insight into its effectiveness. Other options do not represent the correct approach to calculating the ARR. The rate of complications in the treatment group, the percentage of patients who improved in the control group, and the average treatment outcome in each group do not directly compare the risk between both groups in the way that ARR is meant to illustrate. This distinction is crucial for understanding the efficacy of treatments in