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Difficulty: EasyStudy Design

A physician at a community clinic is interested in the long-term health outcomes of a popular high-protein diet. She identifies 500 healthy adult patients in her practice who report strictly following this diet and 500 healthy adults of similar ages who consume a standard diet. At the time of enrollment, none of the 1,000 patients have a history of cardiovascular disease. The physician plans to review their medical records annually for the next 10 years to determine the incidence of new-onset hypertension and myocardial infarction in both groups. Which of the following best describes this study design?

  1. A
    Case-control study
  2. B
    Cross-sectional study
  3. Prospective cohort studyAnswer
  4. D
    Randomized controlled trial
  5. E
    Retrospective cohort study

Answer

Prospective cohort study
The correct answer is a prospective cohort study. In this scenario, the physician groups patients based on their current exposure status (high-protein diet vs. standard diet). Crucially, the patients are free of the outcome (cardiovascular disease) at the start of the study. The physician then follows these groups forward in time (for 10 years) to measure the incidence of the outcome. This forward-looking, observational design based on exposure is the definitive structure of a prospective cohort study.

Step-by-Step Solution

1
Determine how the study groups were initially formed.
The patients were grouped based on their exposure status: following a high-protein diet versus following a standard diet.
Identifying the initial grouping (by exposure vs. by outcome) distinguishes cohort studies from case-control studies.
2
Determine the role of the investigator in assigning the exposure.
The investigator did not assign the diet; the patients were already following it.
This confirms the study is observational rather than experimental (like a randomized controlled trial).
3
Analyze the direction of time in the study.
The patients are being followed forward in time for 10 years to see if they develop the outcome (cardiovascular disease).
Following patients forward from the present to the future differentiates a prospective cohort study from a retrospective cohort study.

Key Concept

A prospective cohort study identifies individuals based on their exposure status at the present time and follows them forward in time to observe the incidence of a specific disease or outcome.
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Study Design

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