Odds Ratio Calculator
Compute the odds ratio OR = a·d/(b·c) and its 95% confidence interval from a 2×2 table.
Input Data
Exposed with outcome.
Exposed without outcome.
Unexposed with outcome.
Unexposed without outcome.
Results
1.5556
0.866
2.7941
At a glance:OR = a·d / (b·c); 95% CI via ln(OR) ± 1.96·√(1/a+1/b+1/c+1/d).
Formula
OR = (a/b) / (c/d) = (ad)/(bc)
$$OR = \frac{a/b}{c/d} = \frac{ad}{bc}$$How to Use
- Fill in the four cell counts a, b, c, d of the 2×2 table.
- The calculator outputs the OR.
- Read the 95% confidence interval (lower/upper).
- If the interval excludes 1, the association is significant at the 5% level.
FAQ
How is OR different from relative risk (RR)?
OR compares the ratio of odds; RR compares the ratio of probabilities. They are similar when the outcome is rare, but OR overestimates RR when the outcome is common. Case-control studies report OR because RR cannot be estimated directly.
What does OR = 1 mean?
OR=1 means no association between exposure and outcome; OR>1 means exposure increases the odds of the outcome; OR<1 means exposure is protective.
References
Content reviewed by the Calculatorism editorial team. Results are for reference only; please refer to the relevant authorities for the official figures.