Kennedy, Edward HJoffe, Marshall MSmall, Dylan S2023-05-232023-05-232015-02-012018-07-16https://repository.upenn.edu/handle/20.500.14332/48039Efficient semiparametric estimation of longitudinal causal effects is often analytically or computationally intractable. We propose a novel restricted estimation approach for increasing efficiency, which can be used with other techniques, is straightforward to implement, and requires no additional modeling assumptions.© 2015 Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license (http://creativecommons.org/licenses/by-nc-nd/4.0/)doubly robustgeneralized method of momentsmarginal structural modelsemiparametric efficiencystructural nested modeltime-varying confoundingBusinessBusiness AnalyticsHealth Services AdministrationHealth Services ResearchMedical HumanitiesStatistics and ProbabilityArticle