1. What is Absolute Risk Reduction?

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

2. How Does the Calculator Work?

The calculator uses the ARR formula:

Where:

• \( CER \) — Control Event Rate (0 to 1)
• \( TER \) — Treatment Event Rate (0 to 1)

Explanation: ARR shows the actual difference in risk between two 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 treatment effects, calculating Number Needed to Treat (NNT), and making informed treatment decisions.

4. Using the Calculator

Tips: Enter both CER and TER as proportions between 0 and 1 (e.g., 0.25 for 25%). The calculator will compute the absolute difference.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between ARR and RRR?
A: ARR shows absolute difference (CER - TER), while RRR (Relative Risk Reduction) shows percentage reduction ((CER-TER)/CER).

Q2: How is ARR related to NNT?
A: Number Needed to Treat (NNT) is the reciprocal of ARR (NNT = 1/ARR), showing how many patients need treatment to prevent one event.

Q3: What's a good ARR value?
A: Depends on context. Higher ARR means greater treatment benefit. Values above 0.1 (10%) are generally considered clinically significant.

Q4: When is ARR most useful?
A: When event rates are moderate to high. For rare events, ARR will be small even if relative effect is large.

Q5: Can ARR be negative?
A: Yes, negative ARR indicates treatment increases risk (harm) compared to control.