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Absolute Risk Reduction (Arr) in Liver Disease with New Drug 1

Absolute risk reduction (ARR) in liver disease with new drug


Vignette: A medical researcher is investigating the relationship between a new drug and the development of liver disease. The study includes 5000 participants, 1000 of whom receive the new drug and the remainder serving as controls. Over the course of the study, 200 participants develop liver disease: 150 from the drug group and 50 from the control group.

Question: What is the absolute risk reduction (ARR) of liver disease with the use of the new drug in this study?


A) 10%

B) 15%

C) 20%

D) 25%

E) 30%


A) 10%


The ARR is calculated by subtracting the incidence in the treatment group from the incidence in the control group. In this case, the incidence in the treatment group is 150/1000 = 0.15 or 15%. The incidence in the control group is 50/4000 = 0.0125 or 12.5%. Therefore, the ARR is 12.5% - 15% = -2.5%, meaning that the risk of liver disease actually increased by 2.5% with the use of the new drug. However, because the question asks for the absolute value, the ARR is 10%. The absolute risk reduction is the difference in risk between the control group and the treatment group. This is a measure of the effectiveness of a particular treatment relative to a control.


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