title: Pseudo-empirical Likelihood-Based Method Using Calibration for Longitudinal Data with Drop-Out.
abstract: In observational studies, interest mainly lies in estimation of the population-level relationship between the explanatory variables and dependent variables, and the estimation is often undertaken using a sample of longitudinal data. In some situations, the longitudinal data sample features biases and loss of estimation efficiency due to non-random drop-out. However, inclusion of population-level information can increase estimation efficiency. In this paper we propose an empirical likelihood-based method to incorporate population-level information in a longitudinal study with drop-out. The population-level information is incorporated via constraints on functions of the parameters, and non-random drop-out bias is corrected by using a weighted generalized estimating equations method. We provide a three-step estimation procedure that makes computation easier. Some commonly used methods are compared in simulation studies, which demonstrate that our proposed method can correct the non-random drop-out bias and increase the estimation efficiency, especially for small sample size or when the missing proportion is high. In some situations, the efficiency improvement is substantial. Finally, we apply this method to an Alzheimer's disease study.
authors.affiliation: Department of Biostatistics, University of Nebraska Medical Center, Omaha, NE, US 68198 baojiang.chen@unmc.edu.
authors.forename: Baojiang
authors.initials: B
authors.lastname: Chen
authors.affiliation: Department of Biostatistics, University of Washington, Seattle, Washington, US 98195 Northwest HSR&D Center of Excellence, VA Puget Sound Health Care System, Metropolitan Park West, 1100 Olive Way #1400, Seattle, WA 98101 azhou@u.washington.edu.
authors.forename: Xiao-Hua
authors.initials: XH
authors.lastname: Zhou
authors.affiliation: Department of Biostatistics, University of Washington, Seattle, Washington, US 98195 kcgchan@u.washington.edu.
authors.forename: Kwun Chuen Gary
authors.initials: KC
authors.lastname: Chan
keywords: Calibration; drop-out; empirical likelihood; longitudinal data