title: Variable selection for semiparametric mixed models in longitudinal studies.
abstract: We propose a double-penalized likelihood approach for simultaneous model selection and estimation in semiparametric mixed models for longitudinal data. Two types of penalties are jointly imposed on the ordinary log-likelihood: the roughness penalty on the nonparametric baseline function and a nonconcave shrinkage penalty on linear coefficients to achieve model sparsity. Compared to existing estimation equation based approaches, our procedure provides valid inference for data with missing at random, and will be more efficient if the specified model is correct. Another advantage of the new procedure is its easy computation for both regression components and variance parameters. We show that the double-penalized problem can be conveniently reformulated into a linear mixed model framework, so that existing software can be directly used to implement our method. For the purpose of model inference, we derive both frequentist and Bayesian variance estimation for estimated parametric and nonparametric components. Simulation is used to evaluate and compare the performance of our method to the existing ones. We then apply the new method to a real data set from a lactation study.
authors.affiliation: Discovery Analytics, GlaxoSmithKline, Five Moore Drive, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Xiao
authors.initials: X
authors.lastname: Ni
authors.forename: Daowen
authors.initials: D
authors.lastname: Zhang
authors.forename: Hao Helen
authors.initials: HH
authors.lastname: Zhang
mesh_terms: D000465:Algorithms; D001499:Bayes Theorem; D001699:Biometry / Q000379:methods*; D003198:Computer Simulation; D003627:Data Interpretation, Statistical; D004812:Epidemiologic Methods; D016247:Information Storage and Retrieval / Q000379:methods*; D008137:Longitudinal Studies; D015233:Models, Statistical