The odds ratio (OR) is a measure of association that is used to describe the relationship between two or more categorical (usually dichotomous) variables (e.g., in a contingency table) or between continuous variables and a categorical outcome variable (e.g., in logistic regression). The OR describes how much more likely an outcome is to occur in one group as compared to another group. ORs are particularly important in research settings that have dichotomous outcome variables (e.g., in medical research).

As the name implies, the OR is the ratio of two “odds,” which are, in turn, ratios of the chance or probability of two (or more) possible outcomes. Suppose one were throwing a single die and wanted to calculate the odds of getting a 1, 2, 3, or ...

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