What does the odds ratio (OR) measure in case-control studies?

The odds ratio (OR) is a statistical measure used in case-control studies to quantify the strength of the association between an exposure and an outcome, typically a disease. Specifically, it compares the odds of exposure in cases (those with the disease) to the odds of exposure in controls (those without the disease).

When researchers calculate the OR, they aim to determine whether there is a higher or lower likelihood of having been exposed to a certain factor among those who have the disease compared to those who do not. An OR greater than 1 suggests a positive association, indicating that the exposure might be a risk factor for the disease. An OR less than 1 indicates a negative association, suggesting the exposure may be protective against the disease.

This measurement is particularly valuable because it allows for assessments of risk factors when directly measuring rates of disease incidence (as may be done in cohort studies) is not feasible. Therefore, the odds ratio is a fundamental tool in understanding the relationship between exposure and disease in the context of case-control studies.