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Absolute Risk Reduction Formula:
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Absolute Risk Reduction (ARR) is the difference in event rates between control and experimental groups in clinical trials. It represents the absolute difference in risk of an outcome between two groups and is a key 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 a percentage point difference.
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 Control Event Rate and Experimental Event Rate as percentages (0-100%). Positive ARR values indicate risk reduction, while negative values indicate increased risk.
Q1: What is the difference between ARR and RRR?
A: ARR is the absolute difference in event rates, while Relative Risk Reduction (RRR) is the proportional reduction in risk relative to the control group.
Q2: How is ARR related to NNT?
A: Number Needed to Treat (NNT) = 1/ARR (when ARR is expressed as a decimal). NNT represents how many patients need treatment to prevent one additional bad outcome.
Q3: What is a clinically significant ARR?
A: Clinical significance depends on the context - the disease severity, treatment risks, and costs. Generally, larger ARR values indicate more effective interventions.
Q4: Can ARR be negative?
A: Yes, negative ARR indicates the experimental treatment increases risk compared to control, which may occur with harmful interventions.
Q5: When should ARR be used instead of RRR?
A: ARR provides a more realistic picture of treatment benefit for clinical decision-making, while RRR can sometimes overestimate the apparent treatment effect.