Odds ratio calculator
Enter a 2×2 table of exposure by event. Everything is calculated in your browser.
Relative risk (not the odds ratio), from the raw counts: 2.000
Questions
How is the odds ratio calculated?
The odds ratio is (a×d)/(b×c): the odds of the event in the exposed group divided by the odds in the unexposed group. A value above 1 means higher odds with exposure.
What happens when a cell is zero?
The odds ratio or its standard error is undefined with a zero cell, so this page adds 0.5 to every cell (the Haldane–Anscombe correction) and uses those cells for both the OR and the CI.
Is the odds ratio the same as relative risk?
No. Relative risk compares event proportions; the odds ratio compares odds. They are close when the event is rare and diverge when it is common. The odds ratio here is also unadjusted for confounders.
Educational only. Not medical advice, not a regulatory determination, and not a substitute for qualified RA/QA, legal, clinical, or statistical counsel. Odds ratio calculator does not submit to FDA, Notified Bodies, or IRBs. This is a 2×2 summary, not a diagnosis and not adjusted for confounders.