1. What is Absolute Risk Reduction?

Absolute Risk Reduction (ARR) is the difference in risk between the control group and the experimental group in a clinical trial. It represents the absolute difference in event rates and is expressed as a percentage.

2. How Does the Calculator Work?

The calculator uses the ARR formula:

Where:

• \( CER \) — Control Event Rate (proportion)
• \( EER \) — Experimental Event Rate (proportion)
• \( ARR \) — Absolute Risk Reduction (percentage)

Explanation: The formula calculates the absolute difference in event rates between control and experimental groups, multiplied by 100 to convert to percentage.

3. Importance of ARR Calculation

Details: ARR is crucial for understanding the clinical significance of treatment effects, calculating Number Needed to Treat (NNT), and making informed medical decisions about interventions.

4. Using the Calculator

Tips: Enter both CER and EER as proportions between 0 and 1. For example, if 30% of control group had the event, enter 0.30.

5. Frequently Asked Questions (FAQ)

Q1: What is the difference between ARR and RRR?
A: ARR shows absolute difference in risk, while RRR (Relative Risk Reduction) shows the proportional reduction in risk relative to control group.

Q2: How is ARR related to NNT?
A: Number Needed to Treat (NNT) = 1/ARR. It represents how many patients need to be treated to prevent one additional bad outcome.

Q3: What is a clinically significant ARR?
A: Clinical significance depends on the condition and intervention. Generally, larger ARR values indicate more effective treatments.

Q4: Can ARR be negative?
A: Yes, negative ARR indicates the experimental treatment is worse than control, which would be called Absolute Risk Increase (ARI).

Q5: When should ARR be used instead of RRR?
A: ARR is preferred for clinical decision-making as it provides the actual risk difference, while RRR can be misleading when baseline risk is low.