title: Robust Bayesian inference for multivariate longitudinal data by using normal/independent distributions.
abstract: Many randomized clinical trials collect multivariate longitudinal measurements in different scales, for example, binary, ordinal, and continuous. Multilevel item response models are used to evaluate the global treatment effects across multiple outcomes while accounting for all sources of correlation. Continuous measurements are often assumed to be normally distributed. But the model inference is not robust when the normality assumption is violated because of heavy tails and outliers. In this article, we develop a Bayesian method for multilevel item response models replacing the normal distributions with symmetric heavy-tailed normal/independent distributions. The inference is conducted using a Bayesian framework via Markov Chain Monte Carlo simulation implemented in BUGS language. Our proposed method is evaluated by simulation studies and is applied to Earlier versus Later Levodopa Therapy in Parkinson's Disease study, a motivating clinical trial assessing the effect of Levodopa therapy on the Parkinson's disease progression rate.
authors.affiliation: Division of Biostatistics, University of Texas School of Public Health, 1200 Pressler St, Houston, Texas 77030, U.S.A.
authors.forename: Sheng
authors.initials: S
authors.lastname: Luo
authors.forename: Junsheng
authors.initials: J
authors.lastname: Ma
authors.forename: Karl D
authors.initials: KD
authors.lastname: Kieburtz
mesh_terms: D001499:Bayes Theorem; D003198:Computer Simulation; D006801:Humans; D007980:Levodopa / Q000008:administration & dosage / Q000627:therapeutic use; D008137:Longitudinal Studies / Q000379:methods*; D008390:Markov Chains; D015233:Models, Statistical; D009010:Monte Carlo Method; D015999:Multivariate Analysis; D010300:Parkinson Disease / Q000188:drug therapy / Q000523:psychology; D011788:Quality of Life / Q000523:psychology; D016032:Randomized Controlled Trials as Topic / Q000379:methods*
chemical_list: D007980:Levodopa
keywords: Markov Chain Monte Carlo; clinical trial; item response theory; latent variable; robust inference