To test whether intense mobile phone use immediately before driving raises crash risk, researchers enroll drivers involved in collisions and compare each driver's phone use in the hour before the crash with the same driver's phone use during an earlier, comparable hour without a crash. Each subject thus acts as his or her own control. This design is:

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

Explanation

The case-crossover design, introduced by Maclure, examines whether a transient exposure triggers an acute event by using each subject as his or her own control: the hazard period just before the event is compared with earlier control periods. Because self-matching eliminates between-person confounding, it suits intermittent exposures with immediate effects such as exertion, drug ingestion, or phone use preceding a myocardial infarction or crash. It is unsuited to stable exposures.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.