A ratio comparing the odds of an outcome between two groups.
The odds ratio expresses how much more (or less) likely an outcome is in one group compared with another, calculated as the odds of the event in the exposed/treatment group divided by the odds in the comparison group. An OR of 1 indicates no difference, values above 1 suggest greater odds of the outcome, and values below 1 suggest lower odds. It approximates relative risk well when the outcome is rare, but can overstate the effect size when the outcome is common, so it should be interpreted alongside baseline event rates.
This guide was auto-drafted and is pending editorial review.