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Absolute Risk Increase Formula:
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Absolute Risk Increase (ARI) is a measure used in clinical trials and epidemiology to quantify the difference in risk between experimental and control groups. It represents the absolute difference in event rates between two groups.
The calculator uses the ARI formula:
Where:
Explanation: ARI shows the actual increase in risk attributable to the experimental intervention compared to the control group.
Details: ARI is crucial for understanding the clinical significance of treatment effects, calculating Number Needed to Harm (NNH), and making informed decisions about risk-benefit ratios in medical interventions.
Tips: Enter both EER and CER as fractions between 0 and 1. For example, 0.15 represents 15% event rate. Ensure EER is greater than CER for meaningful ARI interpretation.
Q1: What Is The Difference Between ARI And RRI?
A: ARI measures absolute difference in risk, while Relative Risk Increase (RRI) measures proportional increase: RRI = (EER - CER) / CER.
Q2: How Is ARI Related To NNH?
A: Number Needed to Harm (NNH) is the reciprocal of ARI: NNH = 1 / ARI. It represents the number of patients needed to be treated for one additional harmful event to occur.
Q3: When Is ARI Most Useful?
A: ARI is particularly valuable when assessing adverse effects of treatments or interventions where the risk increase needs to be understood in absolute terms.
Q4: Can ARI Be Negative?
A: Yes, if EER is less than CER, ARI becomes negative, indicating an Absolute Risk Reduction (ARR) instead of increase.
Q5: What Are Typical ARI Values In Clinical Practice?
A: ARI values vary widely depending on the intervention and outcome. Values range from very small (0.001-0.01) for rare events to larger values (0.1-0.3) for more common adverse effects.