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 actual reduction in risk attributable to the intervention, calculated from Relative Risk Reduction (RRR) and Control Event Rate (CER).

2. How Does the Calculator Work?

The calculator uses the ARR formula:

Where:

• \( ARR \) — Absolute Risk Reduction (proportion)
• \( RRR \) — Relative Risk Reduction (decimal)
• \( CER \) — Control Event Rate (decimal)

Explanation: ARR provides the actual clinical benefit by showing how much the risk is reduced in absolute terms, which is often more meaningful than relative measures alone.

3. Importance of ARR Calculation

Details: ARR is crucial for understanding the real-world impact of treatments, calculating Number Needed to Treat (NNT), and making informed clinical decisions about treatment benefits versus risks.

4. Using the Calculator

Tips: Enter RRR and CER as decimals between 0 and 1. For example, 25% RRR should be entered as 0.25, and 15% CER should be entered as 0.15.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between ARR and RRR?
A: RRR shows the proportional reduction in risk, while ARR shows the actual difference in event rates. ARR is generally more clinically meaningful.

Q2: How do I convert ARR to Number Needed to Treat (NNT)?
A: NNT = 1 / ARR. For example, if ARR is 0.05, NNT = 1 / 0.05 = 20.

Q3: When is ARR more useful than RRR?
A: ARR is more useful when baseline risk is low, as RRR can make small absolute benefits appear large in relative terms.

Q4: Can ARR be negative?
A: Yes, negative ARR indicates the treatment may be harmful, showing an increase in risk compared to control.

Q5: How should I interpret ARR values?
A: Larger ARR values indicate greater treatment benefit. Values are typically interpreted in clinical context considering treatment risks and costs.