1. What is Absolute Risk Increase?

Absolute Risk Increase (ARI) is the difference in risk between control and experimental groups in clinical studies. It measures the absolute change in risk attributable to an intervention or exposure.

2. How Does the Calculator Work?

The calculator uses the ARI formula:

Where:

• \( ARI \) — Absolute Risk Increase (%)
• \( CER \) — Control Event Rate (%)
• \( EER \) — Experimental Event Rate (%)

Explanation: A positive ARI indicates increased risk in the control group, while a negative ARI indicates increased risk in the experimental group.

3. Importance of ARI Calculation

Details: ARI provides a clear measure of the absolute difference in risk between groups, which is essential for clinical decision-making, risk-benefit analysis, and treatment recommendations.

4. Using the Calculator

Tips: Enter both control event rate and experimental event rate as percentages. Values should be between 0 and 100. The calculator will compute the absolute difference in risk.

5. Frequently Asked Questions (FAQ)

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

Q2: When is ARI most useful?
A: ARI is particularly useful when baseline risks are high, as it provides a more clinically meaningful measure of treatment effect than relative measures.

Q3: How do I interpret negative ARI values?
A: Negative ARI indicates the experimental treatment increases risk compared to control, which may represent harm or adverse effects.

Q4: What are typical ARI values in clinical studies?
A: ARI values vary widely depending on the intervention and condition, ranging from small fractions of a percent to several percentage points.

Q5: How does ARI relate to NNT?
A: Number Needed to Treat (NNT) is the reciprocal of ARI (NNT = 1/ARI), representing the number of patients needed to treat to prevent one additional bad outcome.