The odds-ratio and risk-ratio effect sizes (OR and RR) are designed for contrasting two groups on a binary (dichotomous) dependent variable. It can be computed from 2 by 2 frequency tables or from outcome event proportions for each group. With the marginal distributions, it can be comptued from a chi-square and a phi coefficient. A method is also provided to estimate an approximate odds-ratio from a standardized mean difference effect size.
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