Odds-Ratio

The odds of an event happening in one group divided by the odds of an event happening in another group. It is literally the ratio of two odds. It acts like effect size for a chi-square. The chi-square tells you if there is a difference – the odds ratio tells you how big/strong that difference is. If the chi-square is significant – the odds ratio is also statistically significant. Literal interpretation is how much more likely an event is to happen in one group versus another. It’s easier to see in our example…