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Epidemiology. 2007 Sep;18(5):561-8.

Four types of effect modification: a classification based on directed acyclic graphs.

Author information

1
Department of Health Studies, University of Chicago, Chicago, Illinois 60637, USA. vanderweele@uchicago.edu

Abstract

It is possible to classify the types of causal relationships that can give rise to effect modification on the risk difference scale by expressing the conditional causal risk-difference as a sum of products of stratum-specific risk differences and conditional probabilities. Directed acyclic graphs clarify the causal relationships necessary for a particular variable to serve as an effect modifier for the causal risk difference involving 2 other variables. The directed acyclic graph causal framework thereby gives rise to a 4-fold classification for effect modification: direct effect modification, indirect effect modification, effect modification by proxy and effect modification by a common cause. We briefly discuss the case of multiple effect modification relationships and multiple effect modifiers as well as measures of effect other than that of the causal risk difference.

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PMID:
17700242
DOI:
10.1097/EDE.0b013e318127181b
[Indexed for MEDLINE]

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