Compatible Imputation for Hierarchical Linear Models with Incomplete Data: Interaction Effects of Continuous and Categorical Covariates MAR

Abstract

This article focuses on Bayesian estimation of a hierarchical linear model (HLM) from incomplete data assumed missing at random where continuous covariates C and discrete categorical covariates $D$ have interaction effects on a continuous response $R$. Given small sample sizes, maximum likelihood estimation is suboptimal, and existing Gibbs samplers are based on a Bayesian joint distribution compatible with the HLM, but impute missing values of $C$ and the underlying latent continuous variables $D^*$ of $D$ by a Metropolis algorithm via proposal normal densities having constant variances while the target conditional distributions of $C$ and $D$ have nonconstant variances. Therefore, the samplers are neither guaranteed to be compatible with the joint distribution nor ensured to always produce unbiased estimation of the HLM. We assume a Bayesian joint distribution of parameters and partially observed variables, including correlated categorical $D$, and introduce a compatible Gibbs sampler that draws parameters and missing values directly from the exact posterior distributions. We apply our sampler to incompletely observed longitudinal data from the small number of patient-physician encounters during office visits, and compare our estimators with those of existing methods by simulation.