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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 size.
The calculator uses the ARR formula:
Where:
Explanation: ARR measures the actual reduction in risk attributable to the intervention, expressed as a percentage difference between control and experimental 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 treatment benefits.
Tips: Enter both CER and EER as percentages (0-100%). Positive ARR values indicate risk reduction, while negative values indicate increased risk in the experimental group.
Q1: What is the difference between ARR and RRR?
A: ARR is the absolute difference in risk, while RRR (Relative Risk Reduction) is the proportional reduction relative to control risk. ARR provides more clinically meaningful information.
Q2: How is ARR related to NNT?
A: Number Needed to Treat (NNT) = 1/ARR. NNT represents how many patients need to be treated to prevent one additional bad outcome.
Q3: What is a clinically significant ARR?
A: Clinical significance depends on the context. Larger ARR values indicate greater treatment benefit. Generally, ARR > 5% is considered clinically important for many outcomes.
Q4: When is ARR preferred over RRR?
A: ARR is preferred for clinical decision-making as it provides the actual magnitude of benefit. RRR can be misleading when control event rates are low.
Q5: 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).