An investigator studies whether intense physical exertion triggers acute myocardial infarction. For each patient hospitalised with MI, she compares the level of exertion during the 2 hours preceding symptom onset with that patient's usual exertion level during the same 2-hour window on prior days. Each subject thus serves as his or her own control. This design is called:

• A Crossover randomized trial
• B Cross-sectional study
• C Case-crossover study ✓
• D Historical cohort study

Explanation

The case-crossover design is built for transient, short-lived exposures acting as triggers of acute outcomes. Each case alternates between a hazard period just before the event and control periods, so time-invariant confounders such as genotype, personality and chronic habits are controlled by self-matching. A crossover trial involves intervention sequences assigned by the investigator, which is impossible here because the exposure cannot be ethically or practically assigned.

Reference: Modern Epidemiology (Rothman), 4th ed.

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Written and medically reviewed by the StethoPrep medical team.