1. What is Absolute Risk Reduction?

Absolute Risk Reduction (ARR) is the difference in event rates between control and treatment groups in clinical trials. It represents the absolute benefit or harm of an intervention compared to control.

2. How Does the Calculator Work?

The calculator uses the ARR approximation formula:

Where:

• \( OR \) — Odds Ratio
• \( CER \) — Control Event Rate (as fraction)
• \( ARR \) — Absolute Risk Reduction (output as fraction)

Explanation: This formula approximates ARR from odds ratio and control event rate, providing a quick estimate when individual patient data is unavailable.

3. Importance of ARR Calculation

Details: ARR provides a more clinically meaningful measure of treatment effect than relative measures like odds ratio. It helps clinicians and patients understand the actual benefit of an intervention.

4. Using the Calculator

Tips: Enter odds ratio as a positive number (e.g., 0.5 for protective effect, 2.0 for harmful effect). Control event rate should be between 0 and 1 (e.g., 0.15 for 15% event rate).

5. Frequently Asked Questions (FAQ)

Q1: What is the difference between ARR and RRR?
A: ARR is the absolute difference in event rates, while RRR (Relative Risk Reduction) is the proportional reduction. ARR is often more clinically relevant.

Q2: When is this approximation most accurate?
A: The approximation works best when event rates are low to moderate (CER < 0.3) and odds ratios are close to 1.

Q3: Can ARR be negative?
A: Yes, negative ARR indicates the treatment increases risk compared to control (harmful effect).

Q4: How do I convert ARR to NNT?
A: Number Needed to Treat (NNT) = 1 / ARR (when ARR is expressed as decimal).

Q5: What are the limitations of this approximation?
A: This is an approximation and may not be accurate for extreme odds ratios or very high control event rates. For precise calculations, individual patient data is preferred.