Home
Back
ARI Formula:
| From: | To: |
Absolute Risk Increase (ARI) is an epidemiological measure that quantifies the difference in risk between an experimental group and a control group. It represents the absolute difference in event rates between two groups being compared.
The calculator uses the ARI formula:
Where:
Explanation: A positive ARI indicates increased risk in the experimental group, while a negative ARI indicates decreased risk (Absolute Risk Reduction).
Details: ARI is crucial in clinical trials and epidemiological studies for understanding the absolute magnitude of risk difference between interventions. It provides a more intuitive measure of treatment effect than relative measures.
Tips: Enter both EER and CER as fractions between 0 and 1. For example, 0.15 represents 15% event rate. Ensure values are valid fractions within the 0-1 range.
Q1: What is the difference between ARI and RRI?
A: ARI measures absolute difference in risk, while Relative Risk Increase (RRI) measures the proportional increase in risk relative to the control group.
Q2: When is ARI most useful?
A: ARI is particularly useful for clinical decision-making as it provides the actual magnitude of risk difference that patients and clinicians can understand directly.
Q3: Can ARI be negative?
A: Yes, a negative ARI indicates that the experimental treatment reduces risk compared to control, which is then called Absolute Risk Reduction (ARR).
Q4: How does ARI relate to NNT?
A: Number Needed to Treat (NNT) is the reciprocal of ARR (1/ARR) when ARI is negative, representing how many patients need to be treated to prevent one adverse event.
Q5: What are the limitations of ARI?
A: ARI doesn't account for baseline risk and may be less informative when control event rates vary significantly across populations.