Home
Back
Absolute Risk Reduction Formula:
| From: | To: |
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.
The calculator uses the ARR formula:
Where:
Explanation: ARR measures the actual reduction in risk attributable to the intervention, expressed as an absolute difference between the two groups.
Details: ARR is crucial for understanding the clinical significance of treatment effects, calculating Number Needed to Treat (NNT), and making informed clinical decisions about therapeutic interventions.
Tips: Enter both CER and EER as fractions between 0 and 1. For example, 0.15 represents 15% risk. Ensure CER is greater than EER for meaningful ARR interpretation.
Q1: What is the difference between ARR and RRR?
A: ARR shows absolute difference in risk, while Relative Risk Reduction (RRR) shows proportional reduction. ARR is generally more clinically meaningful.
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 bad outcome.
Q3: What constitutes a clinically significant ARR?
A: Clinical significance depends on the condition and intervention. Generally, larger ARR values indicate more effective treatments, but context matters.
Q4: Can ARR be negative?
A: Yes, negative ARR indicates the experimental treatment increases risk compared to control, which would be reported as Absolute Risk Increase (ARI).
Q5: When should ARR be used instead of other measures?
A: ARR is preferred when you need to understand the actual magnitude of risk difference for clinical decision-making and patient communication.