Absolute Risk Reduction Calculation

Absolute Risk Reduction Formula:

\[ ARR = CER - EER \]

Absolute Risk Reduction (ARR):

Risk Reduction (Fraction):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Absolute Risk Reduction?

Absolute Risk Reduction (ARR) is the difference in risk between the control group and the experimental group in a clinical trial. It represents the absolute difference in event rates and provides a clear measure of treatment effect.

2. How Does the Calculator Work?

The calculator uses the ARR formula:

\[ ARR = CER - EER \]

Where:

\( CER \) — Control Event Rate (proportion of events in control group)
\( EER \) — Experimental Event Rate (proportion of events in experimental group)
\( ARR \) — Absolute Risk Reduction

Explanation: ARR measures the actual risk reduction attributable to the intervention, expressed as an absolute difference between groups.

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 clinical decisions about intervention benefits.

4. Using the Calculator

Tips: Enter both CER and EER as proportions between 0 and 1. For example, if 20% of control patients had an event, enter 0.20. The calculator will compute ARR and the risk reduction fraction.

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 in events relative to the control group rate.

Q2: How is ARR related to NNT?
A: Number Needed to Treat (NNT) is calculated as 1/ARR. It represents the number of patients needed to treat to prevent one additional adverse event.

Q3: When is ARR more useful than RRR?
A: ARR provides a more clinically meaningful measure when baseline event rates are low, as RRR can appear large even when absolute benefits are small.

Q4: What does a negative ARR indicate?
A: A negative ARR suggests the experimental treatment may be harmful, as the event rate is higher in the experimental group than in the control group.

Q5: How should ARR be interpreted in clinical practice?
A: ARR should be considered alongside confidence intervals, p-values, and clinical context to determine the practical significance of treatment effects.