Odds Ratio Calculator
Compares the odds of an outcome between two groups.
Odds ratio
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Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
Confidence interval —
Odds in group 1 —
Odds in group 2 —
p-value, two-sided —
Reading this —
The formula
OR = (a × d) ÷ (b × c) SE(ln OR) = √(1/a + 1/b + 1/c + 1/d)
The interval is worked out on the log scale (Woolf’s method), then converted back. It is a large-sample method.
What to watch out for
A ratio of 1 means no difference. Above 1 means higher odds in group 1 and below 1 means lower. Here “outcome” can be anything counted: a purchase, a pass, a defect.
Frequently Asked Questions
What is a worked example?
15 with and 85 without in group 1, against 30 and 70 in group 2, gives an odds ratio of 0.412.
What is the difference between an odds ratio and relative risk?
In the same example the risk ratio is 0.5. The two grow apart as the outcome becomes common, and an odds ratio is always further from 1.