Odds Ratio (OR)
Reference work entry
DOI: https://doi.org/10.1007/978-1-4020-5614-7_2420
Synonyms
Cross-product ratio; Relative odds
Definition
Odds ratios are one way of expressing the size of the effect of a treatment on an even rate. The odds of an event are ratio of the probability of occurring to the probability of it not occurring. The odds ratio is the ratio of the odds of an event in the treatment (or exposed) group compared to the odds in the control (or unexposed) group.
$$ \begin{aligned} \text{OR}&=\frac{a / c}{b / d}=\frac{ad}{bc} \\ 95{\%}CI_\text{OR}&=\exp [\ln \text{OR}\pm 1,96SE _{(\ln\text{OR})}] \end{aligned} $$
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© Springer-Verlag 2008