To test whether episodes of anger trigger acute myocardial infarction, researchers enroll patients who suffered an MI and ask them about their activity and emotional state during the two hours before symptom onset, then compare this with the same information collected for identical two-hour windows on previous days. Each patient thus serves as his own control. This design is:

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

Explanation

The case-crossover design suits transient exposures that briefly raise the risk of an abrupt outcome. Exposure frequency in a defined hazard period immediately before the event is compared with the patient's own habitual exposure, so time-invariant confounders are controlled by self-matching. D randomized cross-over trial involves planned intervention sequences and washout periods, which cannot be applied here.

Reference: Park's Textbook of Preventive and Social Medicine, 26th ed.

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