Research Measurements
OR
Odds Ratio
The ratio of odds of an event in the treatment group vs. the control group.
The odds ratio (OR) compares the odds of an event occurring in one group to the odds in another. An OR of 1.0 indicates equal odds; OR > 1.0 indicates higher odds in the treatment group; OR < 1.0 indicates lower odds. Odds ratios are commonly used in case-control studies and meta-analyses where relative risk cannot be directly calculated. For rare events (< 10% incidence), OR approximates RR. For common events, OR tends to exaggerate the effect compared to RR. In supplement meta-analyses, pooled odds ratios with 95% CIs are standard summary measures.