To test whether brief episodes of intense anger act as a trigger for acute myocardial infarction, researchers enrol MI survivors and compare each patient's level of physical activity and emotional state in the two hours preceding symptom onset with the same patient's exposure status at control times such as the same hour on the previous day. Which study design is this?

• A Nested case-control study
• B Case-crossover study ✓
• C Case-cohort study
• D Retrospective cohort study

Explanation

The case-crossover design uses each subject as his or her own control, comparing exposure immediately before an acute event with exposure during a defined control period. It suits transient exposures that trigger short-lived outcomes. A nested case-control study selects unmatched controls sampled from the source cohort's risk set, not self-comparisons. Case-cohort sampling uses a random subcohort as the common comparison group, and a retrospective cohort starts with defined exposure groups, neither of which occurs here.

Reference: Gordis Epidemiology, 6th ed.

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