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Figure 1 | BMC Medical Research Methodology

Figure 1

From: Reducing bias through directed acyclic graphs

Figure 1

The bi-directional arrows in A show the traditional representation of a confounder as being associated with the exposure (X) and outcome. Because confounders must cause (or be a marker for a cause) of both exposure and outcome (see text for rationale based on basic principles), directed acyclic graphs use only unidirectional arrows to show the direction of causation (B).

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