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Difficulty: MediumEpidemiologic Study Designs

Investigators at a multi-center orthopedic institute are evaluating the relationship between preoperative hemoglobin A1c (HbA1c) levels and the incidence of prosthetic joint infections. To conduct the analysis, they access a comprehensive surgical database containing records of all patients who underwent elective total knee arthroplasty between 2018 and 2023. The researchers categorize the identified patients into two groups: those who had a preoperative HbA1c ≥\geq 8.0% and those who had an HbA1c < 8.0%. They then examine the follow-up clinical notes and microbiology reports within the database to calculate and compare the frequency of prosthetic joint infections that occurred within one year of surgery for both groups. Which of the following best describes the study design used in this investigation?

  1. A
    Case-control study
  2. B
    Cross-sectional study
  3. C
    Nested case-control study
  4. D
    Prospective cohort study
  5. Retrospective cohort studyAnswer

Answer

The correct answer is Retrospective cohort study.
The correct answer describes a study design where investigators categorize participants based on an exposure (HbA1c level) and then determine the incidence of the outcome (prosthetic joint infection), using historical data where both the exposure and outcome have already occurred. This is the defining characteristic of a retrospective cohort study.

Step-by-Step Solution

1
Identify how the study participants were initially categorized.
Participants were divided into groups based on their exposure status (preoperative HbA1c levels).
Grouping by exposure rather than outcome distinguishes cohort studies from case-control studies.
2
Determine the temporal relationship between the study initiation and the outcome occurrence.
Both the exposure (surgery between 2018-2023) and the outcome (joint infection within one year) occurred before the investigators began their data analysis.
This historical timeframe distinguishes a retrospective design from a prospective one.
3
Combine the categorization method and the temporal timeline.
A study that groups patients by an exposure in the past and looks for the incidence of an outcome that also occurred in the past is a retrospective cohort study.
This fulfills the criteria for a retrospective cohort design.

Key Concept

In a retrospective cohort study, investigators group subjects by historical exposure status and utilize past records to ascertain the subsequent incidence of the outcome.
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Epidemiologic Study Designs

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