Risk Ratio Calculator
Calculate Risk Ratio from 2x2 Contingency Table
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Risk Ratio Formula
Risk Ratio = [a/(a+b)] / [c/(c+d)]
ln(RR) = ln(a) - ln(a+b) - ln(c) + ln(c+d)
SE(ln(RR)) = √(1/a - 1/(a+b) + 1/c - 1/(c+d))
Risk Ratio is also called Relative Risk (RR)!
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Ensure a, c ≥ 1 for stable calculations (add 0.5 to each cell if any zero).
What is Risk Ratio?
Risk Ratio (Relative Risk) compares the risk of an outcome between exposed and unexposed groups.
Risk Ratio
Relative risk comparison
Confidence Interval
Precision estimate
RR > 1
Higher risk in exposed
RR < 1
Lower risk in exposed
💡 Example: a=20, b=80, c=10, d=90 → Risk1=20/(20+80)=0.20, Risk0=10/(10+90)=0.10, RR=2.0
Applications
Epidemiology
Medicine
Public Health
Clinical Trials
Research
Frequently Asked Questions
What is risk ratio?▼
RR = (a/(a+b))/(c/(c+d)). Measures association by comparing risks. RR=1 no association.
How to interpret risk ratio?▼
RR>1: exposure increases risk. RR<1: exposure decreases risk. RR=1: no association.
What is confidence interval for RR?▼
CI for ln(RR) = ln(RR) ± z×√(1/a - 1/(a+b) + 1/c - 1/(c+d)). Exponentiate.
Risk ratio vs odds ratio?▼
RR directly compares risks (more intuitive). OR compares odds, overestimates RR for common outcomes.
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