title: An application of model-fitting procedures for marginal structural models.
abstract: 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.
authors: Division of Epidemiology, School of Public Health, University of California, Berkeley, CA 94704, USA. kmort@berkeley.edu
authors: Kathleen M
authors: KM
authors: Mortimer
authors: Romain
authors: R
authors: Neugebauer
authors: Mark
authors: M
authors: van der Laan
authors: Ira B
authors: IB
authors: Tager
mesh_terms: D000393:Air Pollutants / Q000009:adverse effects*; D018927:Anti-Asthmatic Agents / Q000627:therapeutic use; D001249:Asthma / Q000188:drug therapy / Q000209:etiology*; D002140:California / Q000453:epidemiology; D002648:Child; D004812:Epidemiologic Methods; D006801:Humans; D015233:Models, Statistical; D010366:Peak Expiratory Flow Rate / Q000187:drug effects*; D012135:Respiratory Sounds / Q000209:etiology
chemical_list: D000393:Air Pollutants; D018927:Anti-Asthmatic Agents