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Difficulty: MediumBias and Confounding in Research

A team of neurologists is conducting a retrospective observational study using electronic health records to evaluate the association between a newly approved calcitonin gene-related peptide (CGRP) antagonist and the incidence of ischemic stroke in patients with chronic migraines. During the planning phase, the investigators identify that a history of severe hypertension is associated with both the likelihood of being prescribed this new medication and an increased risk of ischemic stroke. To prevent this variable from distorting the study's findings, the study protocol explicitly excludes any patient with a prior diagnosis of hypertension from the cohort. Which of the following epidemiological methods are the researchers using to control for this variable?

  1. RestrictionAnswer
  2. B
    Matching
  3. C
    Stratification
  4. D
    Randomization
  5. E
    Multivariable regression

Answer

The correct answer is restriction.
The researchers are controlling for confounding by explicitly excluding participants who possess the confounding characteristic (hypertension). This method, known as restriction, is applied during the design phase of a study to ensure the study population is uniform with respect to the potential confounder, thereby eliminating its ability to distort the association between the exposure and outcome.

Step-by-Step Solution

1
Identify the primary threat to validity described in the scenario.
Severe hypertension is identified as a confounder because it is associated with both the exposure (CGRP antagonist prescription) and the outcome (ischemic stroke).
Recognizing the epidemiological role of hypertension is necessary to understand why the researchers are taking action.
2
Determine the phase of the study in which the researchers are addressing this threat.
The researchers are addressing the confounder during the design (planning) phase by establishing strict inclusion/exclusion criteria.
Differentiating between design-stage controls (e.g., matching, restriction) and analysis-stage controls (e.g., stratification, regression) narrows down the possible answers.
3
Match the specific action to the correct epidemiological term.
Completely excluding any patient with the confounding trait from the study population is defined as restriction.
This confirms the exact methodological term being tested.

Key Concept

Control of confounding at the design stage via restriction
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Topics

Bias and Confounding in Research

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