Which statement about odds ratio is true?

Which statement about odds ratio is true?

• A. OR measures incidence.
• B. OR is used in cohort studies; cannot approximate RR.
• C. OR = odds of exposure among cases / odds of exposure among controls; used in case-control studies or logistic regression; approximates RR when the outcome is rare.
• D. OR cannot be used when the outcome is rare.

Answer: (C)

Odds ratio compares how often exposure is present among those with the outcome versus those without it. It is calculated as the odds of exposure in cases divided by the odds of exposure in controls, making it particularly suited to case-control studies and to logistic regression where the outcome is binary. It does not measure incidence or risk directly—that would be relative risk or risk difference—but it can approximate relative risk when the outcome is rare, because the odds and the actual probabilities become similar in that scenario.

Odds ratio compares how often exposure is present among those with the outcome versus those without it. It is calculated as the odds of exposure in cases divided by the odds of exposure in controls, making it particularly suited to case-control studies and to logistic regression where the outcome is binary. It does not measure incidence or risk directly—that would be relative risk or risk difference—but it can approximate relative risk when the outcome is rare, because the odds and the actual probabilities become similar in that scenario.