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Difficulty: MediumStudy Design

A public health researcher is designing a study to investigate whether short-term use of high-dose oral corticosteroids is associated with an increased risk of acute psychiatric admissions. The outcome of interest is acute, and the suspected trigger is a transient exposure. To comprehensively account for unmeasured time-invariant confounding variables such as genetic predisposition, baseline psychiatric history, and stable socioeconomic factors, the investigator designs a protocol that identifies patients recently admitted for acute psychosis. The frequency of corticosteroid prescriptions in the 30-day period immediately preceding each patient's admission is then compared to the frequency of corticosteroid prescriptions in a 30-day control period exactly one year prior for those exact same individuals. Which of the following best describes this study design?

  1. A
    Retrospective cohort study
  2. B
    Crossover randomized trial
  3. Case-crossover studyAnswer
  4. D
    Matched case-control study
  5. E
    Nested case-control study

Answer

Case-crossover study
The correct answer accurately identifies a study design tailored for transient exposures (short-term corticosteroid use) and acute outcomes (psychiatric admission). By comparing the exposure status during a 'hazard period' just before the event to a 'control period' at a previous time in the exact same individual, the investigator eliminates the influence of time-invariant confounders (e.g., genetics, chronic conditions). This is the hallmark of a case-crossover study.

Step-by-Step Solution

1
Analyze the starting point and directionality of the investigation.
The researcher identifies patients who already have the outcome (acute psychiatric admission) and looks backward at their exposure history, making it a retrospective observational analysis.
Determining the directionality distinguishes cohort studies (exposure to outcome) from case-control and similar backward-looking designs.
2
Evaluate the nature of the control group used in the study.
The investigator compares the exposure in the period immediately before the event to an earlier control period within the exact same individuals.
Recognizing that patients serve as their own controls eliminates traditional case-control studies where different individuals are compared.
3
Synthesize the design features to identify the specific epidemiological method.
An observational study assessing a transient exposure for an acute event, where each case serves as their own control at a different time point to eliminate time-invariant confounding, is characteristic of a case-crossover study.
This confirms the correct study design while ruling out experimental crossover trials.

Key Concept

Case-crossover study design characteristics and indications
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Topics

Study Design

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