Odds Ratio Calculator

This tool works out the odds ratio for a 2 x 2 table and puts a confidence interval around it. Enter the four counts, or a group size and an event rate for each arm, and it returns the odds ratio, its interval from Woolf's standard error on the log scale, a z test, and the relative risk, risk difference and number needed to treat from the same table. When a cell holds zero it adds 0.5 to all four cells, the Haldane-Anscombe correction, and says so. The odds ratio and the relative risk are printed together because they are different numbers and only agree when the outcome is rare.