1. What is Absolute Risk Reduction?

Absolute Risk Reduction (ARR) is the difference in event rates between control and treatment groups in a clinical study. It represents the absolute change in risk attributable to the treatment.

2. How Does the Calculator Work?

The calculator uses the ARR formula:

Where:

• Control Rate — Event rate in control group (0 to 1)
• Treatment Rate — Event rate in treatment group (0 to 1)

Explanation: ARR shows the actual risk difference between groups, unlike relative measures which can exaggerate small absolute differences.

3. Importance of ARR Calculation

Details: ARR is crucial for understanding the clinical significance of study results. It helps determine the Number Needed to Treat (NNT = 1/ARR) and assess treatment impact in real-world terms.

4. Using the Calculator

Tips: Enter both rates as values between 0 and 1 (e.g., 0.25 for 25%). The control rate should typically be higher than the treatment rate for a positive ARR indicating treatment benefit.

5. Frequently Asked Questions (FAQ)

Q1: How does ARR differ from Relative Risk Reduction?
A: ARR shows the absolute difference in risk, while RRR shows the proportional reduction relative to control risk. ARR is generally more clinically meaningful.

Q2: What's a good ARR value?
A: This depends on context. Larger ARR values indicate more effective treatments, but even small ARRs can be important for common or serious conditions.

Q3: Can ARR be negative?
A: Yes, negative ARR indicates the treatment increased risk compared to control.

Q4: How is ARR related to NNT?
A: NNT (Number Needed to Treat) is the inverse of ARR (NNT = 1/ARR). It tells how many patients need treatment to prevent one adverse event.

Q5: When should I use ARR vs other measures?
A: Use ARR when you need to understand the actual clinical impact. Use RRR when comparing effect sizes across studies with different baseline risks.