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ERIC Number: ED519118
Record Type: Non-Journal
Publication Date: 2011
Pages: 10
Abstractor: ERIC
Reference Count: 15
The Threshold of Embedded M Collider Bias and Confounding Bias
Kelcey, Benjamin; Carlisle, Joanne
Society for Research on Educational Effectiveness
Of particular import to this study, is collider bias originating from stratification on retreatment variables forming an embedded M or bowtie structural design. That is, rather than assume an M structural design which suggests that "X" is a collider but not a confounder, the authors adopt what they consider to be a more reasonable position and that is "X" is both a collider and confounder. Accordingly, in this study they examined the extent to which confounder induced bias exceeds collider induced bias. To inform this tradeoff, they quantified the bias from two simple linear model estimators which are asymptotically equivalent to stratification and matching on these variables (alone or with the propensity score) (e.g. Pearl, 2009). More specifically, they examined this tradeoff by quantifying the net bias induced from adjusting for "X" versus the net bias from ignoring it. As a result, stratifying on "X" removes confounding bias but induces collider bias whereas ignoring "X" alleviates collider bias but invokes confounding bias. For that reason, this study quantified the threshold by which collider and confounder bias due to a hypothesized confounder (e.g. "X") is equal. The intention is to provide pragmatic guidance as to the consequences of and the decision to stratify on covariates hypothesized to be confounders and/or colliders. (Contains 7 figures.)
Society for Research on Educational Effectiveness. 2040 Sheridan Road, Evanston, IL 60208. Tel: 202-495-0920; Fax: 202-640-4401; e-mail:; Web site:
Publication Type: Reports - Evaluative
Education Level: Elementary Education; Elementary Secondary Education
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: Society for Research on Educational Effectiveness (SREE)
Identifiers - Location: Michigan
Identifiers - Assessments and Surveys: Iowa Tests of Basic Skills