Enter the control event rate and the experimental event rate into the calculator to determine the absolute risk reduction.
How to interpret the result
ARR is calculated as CER − EER. If the result is positive, the experimental group had a lower event rate than the control group (risk reduction). If the result is negative, the experimental group had a higher event rate (risk increase, often reported as ARI).
When interpreting results, consider the study design, the baseline risk, and statistical uncertainty (such as confidence intervals) rather than relying on a single point estimate.
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Absolute Risk Reduction Formula
The following equation is used to calculate an absolute risk reduction (or increase) as a signed difference in event rates (in percentage points or proportion).
ARR = CER - EER
- Where ARR is the absolute difference in event rates (in % points or proportion); if negative, it indicates an absolute risk increase (ARI)
- CER is the control event rate (in % or proportion)
- EER is the experimental event rate (in % or proportion)
Absolute Risk Reduction Definition
An absolute risk reduction is defined as the difference between the control event rate and the experimental event rate (reported as a percentage point difference or as a proportion).
Absolute Risk Reduction Example
How to calculate absolute risk reduction?
- First, determine the control rate.
Calculate the percentage rate of the control event rate.
- Next, determine the experimental event rate.
Calculate the experimental event rate.
- Finally, calculate the absolute risk reduction.
Calculate the absolute risk reduction using the formula above.
An absolute risk reduction, or ARR for short, is a measure of the absolute difference between a control group and a group receiving a treatment to prevent the event from happening.
Absolute risk is a ratio of the number of people that have a particular event, typically a medical event, compared to the total number of people that it could happen to.
