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Reducing Confounding During Study Design

Lead Author(s): Jeff Martin, MD

Methods for Reducing Confounding During Study Design

The causal diagram below presents ways to prevent or manage confounding during study design.

0402_3dags.JPG

  • You can block or interrupt the association between the confounder and the exposure (shown in the top diagram)
  • You can block or interrupt the association between the confounder and the disease (in the bottom diagram).
  • You can block or interrupt both arms.
There are three main ways to reduce confounding during study design:

1. Randomization

Definition of Randomization:
  • random assignment of subjects to exposure (e.g., treatment) categories 0402_rand.JPG
This will block all association between the confounder and the exposure:

0402_dag_ran.JPG

2. Restriction

Definition of Restriction: Restrict enrollment to only those subjects who have a specific value/range of the confounding variable

This will eliminate:

  • any possible association between the exposure and the confounder
  • any possible association between the disease and confounder
0402_4restrict.JPG

3. Matching

Definition of Matching:
  • Match unexposed or non-case subjects to those of the comparison group (either exposed or cases) in terms of the confounder in question.
Cohort Study: unexposed subjects are matched to exposed subjects according to their values for the potential confounder. 0407_3amatch.JPG

Case Control Study: non-diseased controls are matched to diseased cases on the confounding variable. 3bmatch.JPG



Topic revision: r18 - 04 Jun 2009 - 18:30:07 - MaryB?
 

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