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ARR Formula:
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Absolute Risk Reduction (ARR) is a measure of treatment effect that represents the difference in event rates between control and experimental groups in clinical trials. It quantifies the absolute benefit or harm of an intervention compared to control.
The calculator uses the ARR formula:
Where:
Explanation: ARR represents the absolute difference in event rates between the control group and treatment group. A positive ARR indicates benefit, while a negative ARR indicates harm.
Details: ARR is crucial for understanding the clinical significance of treatment effects, calculating Number Needed to Treat (NNT), and making informed decisions about therapeutic interventions in evidence-based medicine.
Tips: Enter both Control Event Rate and Experimental Event Rate as percentages (0-100%). The calculator will compute the Absolute Risk Reduction, which can be positive (benefit) or negative (harm).
Q1: What's 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. ARR provides more clinically meaningful information.
Q2: How is ARR related to NNT?
A: Number Needed to Treat (NNT) = 1/ARR. For example, an ARR of 5% means NNT = 20 (you need to treat 20 patients to prevent one event).
Q3: When is ARR most useful?
A: ARR is particularly valuable when baseline event rates are high, as it provides a clearer picture of the actual clinical benefit than relative measures.
Q4: Can ARR be negative?
A: Yes, negative ARR indicates the experimental treatment increases risk compared to control, which would be expressed as Absolute Risk Increase (ARI).
Q5: What are typical ARR values in clinical trials?
A: ARR values vary widely by condition and intervention. In cardiovascular prevention, ARR might be 1-3%, while in infectious diseases it could be much higher.