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.


There are three main ways to reduce confounding during study design:

1. Randomization

Definition of Randomization: This will block all association between the confounder and the exposure:


2. Restriction

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

This will eliminate: 0402_4restrict.JPG

3. Matching

Definition of Matching: 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