Enter the control event rate and the experimental event rate into the calculator to determine the absolute risk reduction.

Absolute Risk Reduction Formula

The following equation is used to calculate an absolute risk reduction.


  • Where ARR is the absolute risk reduction (%)
  • CER is the control event rate (%)
  • EER is the experimental event rate (%)

Absolute Risk Reduction Definition

An absolute risk reduction is defined as the difference between the percentage rate of a control event and an experimental rate.

Absolute Risk Reduction Example

How to calculate absolute risk reduction?

  1. First, determine the control rate.

    Calculate the percentage rate of the control event rate.

  2. Next, determine the experimental event rate.

    Calculate the experimental event rate.

  3. Finally, calculate the absolute risk reduction.

    Calculate the absolute risk reduction using the formula above.

What is an absolute risk reduction?

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.

What is an absolute risk?

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.

absolute risk reduction calculator
absolute risk reduction formula