1. What is Absolute Risk Reduction?

Absolute Risk Reduction (ARR) is the difference in event rates between control and experimental groups in clinical trials. It represents the absolute difference in risk of an outcome between two treatment groups.

2. How Does the Calculator Work?

The calculator uses the Absolute Risk Reduction formula:

Where:

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

Explanation: ARR measures the actual reduction in risk attributable to the intervention, expressed as a percentage difference.

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 clinical decisions about intervention benefits.

4. Using the Calculator

Tips: Enter both CER and EER as proportions (values between 0 and 1). For example, if 20% of control group had an event, enter 0.20.

5. Frequently Asked Questions (FAQ)

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

Q2: How is ARR related to NNT?
A: Number Needed to Treat (NNT) = 1/ARR (when ARR is expressed as decimal). NNT indicates how many patients need treatment to prevent one adverse event.

Q3: What is a clinically significant ARR?
A: Clinical significance depends on the context - the condition being treated, severity of outcomes, and treatment risks/costs.

Q4: When is ARR more useful than RRR?
A: ARR is more informative when baseline risks are low, as RRR can exaggerate small absolute benefits.

Q5: Can ARR be negative?
A: Yes, negative ARR indicates the experimental treatment increased risk compared to control.