Relative risk vs Odds ratio and hazard ratio
How to tell Relative risk and Odds ratio and hazard ratio apart when a board question makes them look alike.
RR: risk ratio for cohorts and trials; OR: odds ratio for case-control; HR: hazard ratio for time-to-event survival analysis.
Side by side
Relative risk compares probability of outcome in exposed versus unexposed groups and is natural in cohort trials.
Odds ratio compares odds and is classic for case-control studies; hazard ratio compares event rates over time in survival analysis.
Relative risk compares probability of outcome in exposed versus unexposed groups and is natural in cohort trials.
Odds ratio compares odds and is classic for case-control studies; hazard ratio compares event rates over time in survival analysis.
The trap
RR compares risks; OR compares odds; HR compares time-to-event hazards.
The repair move
Before naming the answer, force the stem through the separator: RR compares risks; OR compares odds; HR compares time-to-event hazards.
Try a free question
CoreA prospective cohort study follows 10,000 individuals (5,000 smokers, 5,000 non-smokers) for 20 years. Over follow-up, 800 smokers develop lung cancer (incidence 16%); 80 non-smokers develop lung cancer (incidence 1.6%). Which measure of association is appropriate?
Show answer and explanation
Answer: A. Relative risk (RR) = 10. Relative risk = incidence in exposed / incidence in unexposed, used in COHORT studies and clinical trials where incidence is directly measured. RR = 1 (no association), >1 (risk factor), <1 (protective). Smokers have RR = 10 for lung cancer (10-fold higher risk).
Why the other choices are tempting
- B. OR is used in case-control studies where incidence is unknown.
- C. HR is from survival analysis (Cox proportional hazards) for time-to-event data.
- D. NNT is from intervention studies.
- E. ARR is absolute risk difference, not relative.
Flashcards
Tap a card to flip it.
What clue supports Relative risk?
Choose Relative risk when the stem gives this pattern: Relative risk compares probability of outcome in exposed versus unexposed groups and is natural in cohort trials.
What clue supports Odds ratio and hazard ratio?
Choose Odds ratio and hazard ratio when the stem gives this contrasting pattern: Odds ratio compares odds and is classic for case-control studies; hazard ratio compares event rates over time in survival analysis.
Quick answers
What is the fastest way to tell Relative risk from Odds ratio and hazard ratio?
RR: risk ratio for cohorts and trials; OR: odds ratio for case-control; HR: hazard ratio for time-to-event survival analysis.
What is the key clue for Relative risk?
Relative risk compares probability of outcome in exposed versus unexposed groups and is natural in cohort trials.
What is the key clue for Odds ratio and hazard ratio?
Odds ratio compares odds and is classic for case-control studies; hazard ratio compares event rates over time in survival analysis.
What is the common trap with Relative risk vs Odds ratio and hazard ratio?
RR compares risks; OR compares odds; HR compares time-to-event hazards.