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Absolute Risk Increase Formula:
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Absolute Risk Increase (ARI) measures the difference in event rates between experimental and control groups in clinical studies. It represents the increase in event rate attributable to the intervention being studied.
The calculator uses the ARI formula:
Where:
Explanation: ARI quantifies the absolute difference in risk between treatment and control groups, providing a clear measure of intervention effect size.
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 percentages (0-100%). Positive ARI values indicate increased risk with intervention, while negative values suggest risk reduction (Absolute Risk Reduction).
Q1: What is the difference between ARI and ARR?
A: ARI (Absolute Risk Increase) measures increased risk from intervention, while ARR (Absolute Risk Reduction) measures decreased risk. ARR = CER - EER.
Q2: How is ARI related to NNH?
A: Number Needed to Harm (NNH) = 1 / ARI (decimal). It represents the number of patients needed to treat for one additional harmful event to occur.
Q3: When is ARI used in clinical practice?
A: ARI is used when evaluating interventions that may cause harm, assessing side effects, and comparing risk-benefit profiles of different treatments.
Q4: What is a clinically significant ARI?
A: Clinical significance depends on context - the severity of the outcome, baseline risk, and available alternatives. Even small ARIs can be important for serious outcomes.
Q5: Can ARI be negative?
A: Yes, a negative ARI indicates that the intervention actually reduces risk, which would then be called Absolute Risk Reduction (ARR).