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Absolute Risk Reduction (Arr) in This Study 1

Absolute risk reduction (ARR) in this study


Vignette: A medical student is conducting a study to determine the efficacy of a new drug in treating hypertension. He selects 100 hypertensive patients and divides them into two groups: 50 patients receive the new drug, and 50 patients receive a placebo. At the end of the study period, he finds that the new drug was effective in treating hypertension in 40 patients, while the placebo was effective in only 20 patients.

Question: What is the absolute risk reduction (ARR) in this study?


A. 10%

B. 20%

C. 30%

D. 40%

E. 50%


B. 20%


The absolute risk reduction (ARR) is calculated by subtracting the incidence of the outcome in the treatment group from the incidence of the outcome in the control group. In this study, the incidence in the treatment group (new drug) is 40 out of 50, or 80%. The incidence in the control group (placebo) is 20 out of 50, or 40%. Therefore, the ARR is 80% - 40% = 40% - 20% = 20%. ARR is a useful measure in demonstrating the effectiveness of a new treatment compared to a control, and it provides a clear and practical understanding of the benefit of the new treatment.


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