title: Robust Bayesian hierarchical model using normal/independent distributions.
abstract: The multilevel item response theory (MLIRT) models have been increasingly used in longitudinal clinical studies that collect multiple outcomes. The MLIRT models account for all the information from multiple longitudinal outcomes of mixed types (e.g., continuous, binary, and ordinal) and can provide valid inference for the overall treatment effects. However, the continuous outcomes and the random effects in the MLIRT models are often assumed to be normally distributed. The normality assumption can sometimes be unrealistic and thus may produce misleading results. The normal/independent (NI) distributions have been increasingly used to handle the outlier and heavy tail problems in order to produce robust inference. In this article, we developed a Bayesian approach that implemented the NI distributions on both continuous outcomes and random effects in the MLIRT models and discussed different strategies of implementing the NI distributions. Extensive simulation studies were conducted to demonstrate the advantage of our proposed models, which provided parameter estimates with smaller bias and more reasonable coverage probabilities. Our proposed models were applied to a motivating Parkinson's disease study, the DATATOP study, to investigate the effect of deprenyl in slowing down the disease progression.
authors.affiliation: Clinical Statistics, GlaxoSmithKline, 1250 South Collegeville Road, Collegeville, PA, 19426, USA.
authors.forename: Geng
authors.initials: G
authors.lastname: Chen
authors.affiliation: Department of Biostatistics, The University of Texas Health Science Center at Houston, 1200 Pressler St, Houston, TX, 77030, USA.
authors.forename: Sheng
authors.initials: S
authors.lastname: Luo
mesh_terms: D001499:Bayes Theorem; D001699:Biometry / Q000379:methods*; D018450:Disease Progression; D006801:Humans; D008137:Longitudinal Studies; D015233:Models, Statistical; D016011:Normal Distribution; D010300:Parkinson Disease / Q000188:drug therapy; D012642:Selegiline / Q000627:therapeutic use
chemical_list: D012642:Selegiline
keywords: Clinical trial; Item-response theory; Latent variable; MCMC; Outliers