To test whether episodes of anger trigger myocardial infarction, researchers interview patients soon after their MI about anger exposure in the two hours preceding the event, and compare this with anger exposure during matched control time periods for the same patient in the preceding week. Each patient serves as his own control. This design is:

• A Nested case-control study
• B Case-crossover study ✓
• C Cross-over randomized trial
• D Case series

Explanation

The case-crossover design suits transient exposures that acutely trigger sudden outcomes such as MI, injury, or asthma attack. Each subject acts as his own control, comparing exposure just before the event with exposure at other specified times, which automatically controls fixed confounders like genetics and chronic traits. A randomized cross-over trial involves deliberate treatment sequences assigned by the investigator, not observational exposure windows.

Reference: Gordis Epidemiology, 6th ed.

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