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Absolute Risk Reduction Formula:
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Absolute Risk Reduction (ARR) is the absolute difference in event probabilities between control and experimental groups. It represents the actual reduction in risk attributable to an intervention or treatment.
The calculator uses the ARR formula:
Where:
Explanation: The formula calculates the absolute difference between the control group's event rate and the experimental group's event rate, expressed as a percentage.
Details: ARR is crucial for understanding the clinical significance of treatment effects, calculating Number Needed to Treat (NNT), and making informed healthcare decisions based on intervention effectiveness.
Tips: Enter both CER and EER as proportions (values between 0 and 1). For example, if 30% of patients experienced an event, enter 0.30. The calculator will output ARR as a percentage.
Q1: What is the difference between ARR and RRR?
A: ARR shows the absolute difference in risk, while Relative Risk Reduction (RRR) shows the proportional reduction in risk compared to the control group.
Q2: How is ARR related to NNT?
A: Number Needed to Treat (NNT) is calculated as 1/ARR (when ARR is expressed as a decimal). 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 - the condition being treated, the severity of outcomes, and the risks/costs of the intervention.
Q4: Can ARR be negative?
A: Yes, a negative ARR indicates that the experimental treatment is worse than the control, meaning it increases the risk of the event.
Q5: When should I use ARR vs other risk measures?
A: ARR is most useful for understanding the absolute benefit of treatment, while RRR may be better for understanding the relative effect size. Both have important roles in clinical decision-making.