Journal Article

An Application of Model-Fitting Procedures for Marginal Structural Models

Kathleen M. Mortimer, Romain Neugebauer, Mark van der Laan and Ira B. Tager

in American Journal of Epidemiology

Published on behalf of Johns Hopkins Bloomberg School of Public Health

Volume 162, issue 4, pages 382-388
Published in print August 2005 | ISSN: 0002-9262
Published online August 2005 | e-ISSN: 1476-6256 | DOI:
An Application of Model-Fitting Procedures for Marginal Structural Models

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Marginal structural models (MSMs) are being used more frequently to obtain causal effect estimates in observational studies. Although the principal estimator of MSM coefficients has been the inverse probability of treatment weight (IPTW) estimator, there are few published examples that illustrate how to apply IPTW or discuss the impact of model selection on effect estimates. The authors applied IPTW estimation of an MSM to observational data from the Fresno Asthmatic Children's Environment Study (2000–2002) to evaluate the effect of asthma rescue medication use on pulmonary function and compared their results with those obtained through traditional regression methods. Akaike's Information Criterion and cross-validation methods were used to fit the MSM. In this paper, the influence of model selection and evaluation of key assumptions such as the experimental treatment assignment assumption are discussed in detail. Traditional analyses suggested that medication use was not associated with an improvement in pulmonary function—a finding that is counterintuitive and probably due to confounding by symptoms and asthma severity. The final MSM estimated that medication use was causally related to a 7% improvement in pulmonary function. The authors present examples that should encourage investigators who use IPTW estimation to undertake and discuss the impact of model-fitting procedures to justify the choice of the final weights.

Keywords: epidemiologic methods; models, statistical; AIC, Akaike Information Criterion; ETA, experimental treatment assignment; IPTW, inverse probability of treatment weight; MSM(s), marginal structural model(s); PEFR, peak expiratory flow rate; RSS, residual sums of squares

Journal Article.  4848 words.  Illustrated.

Subjects: Public Health and Epidemiology

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