To test whether heavy physical exertion acts as a transient trigger of acute myocardial infarction, researchers enroll patients immediately after an MI and compare their activity level in the hour preceding the event with their usual activity level in matched control hours from prior days. This design is:

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

Explanation

The case-crossover design, analogous to a matched case-control analysis, evaluates transient exposures acting close in time to an acute outcome. Each subject serves as his own control, with the hazard period compared with self-selected control periods, thereby controlling fixed personal characteristics such as genotype and chronic habits. B nested case-control or case-cohort design samples from within a cohort for chronic exposure-outcome questions, and a retrospective cohort requires a defined exposed and unexposed population followed through records.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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