Absolute Risk Reduction (ARR)

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Absolute Risk Reduction


The absolute difference (risk difference) in frequency of harmful outcomes between experimental and control groups, calculated as the frequency of harmful outcomes in the control group minus the frequency of harmful outcomes in the experimental group (CER–EER). Typically used to describe a beneficial exposure or intervention (e.g., if 20% of patients in the control group have an adverse event, as do 10% among treated patients, the ARR or risk difference would be 10% expressed as a percentage or 0.10 expressed as a proportion).

Risk Difference
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