An investigator wants to determine whether episodes of heavy physical exertion act as triggers of acute myocardial infarction. For each patient admitted with MI, exposure to strenuous activity in the two hours preceding symptom onset is compared with exposure during identical two-hour windows on previous days. Each patient thus serves as his or her own control. This design is:
- A Case-cohort study
- B Case-crossover study ✓
- C Cross-over randomized trial
- D Retrospective cohort study
Correct answer: B. Case-crossover study
Explanation
The case-crossover design, described by Maclure, is suited to transient exposures precipitating acute outcomes. Each case contributes paired observations: a hazard window immediately before the event and one or more control windows, making the subject his own control and automatically controlling fixed confounders. A case-cohort study samples a comparison subcohort rather than using within-person windows, and a randomized cross-over trial involves deliberate intervention sequences.
Reference: Modern Epidemiology (Rothman, Greenland, Lash), 4th ed.
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