Mixed-effect models to assess consistency and reliability across multiple evaluations

The issue of consistency and reliability arises frequently in applied clinical trials, and there is a considerable amount of literature on this topic. For a continuous random variable, we describe a process to assess whether the mean and variance are the same from one evaluation to the other and we derive the intraclass correlation (ICC) for evaluating consistency in the distributions of paired data. Mixed-effects linear models are applied, and these procedures are illustrated using dietary recall data from the Girls health Enrichment Multi-site Studies (GEMS). The SAS program code for performing the statistical analysis is provided. The models can be generalized to account for more design factors and other applicable covariates.