Chapter 3: Mood Changes Associated With Smoking in Adolescents: An Application of a Mixed-Effects Location Scale Model for Longitudinal Ecological Momentary Assessment Data

Modern data collection procedures, such as ecological momentary assessments (EMA; Smyth & Stone, 2003; Stone & Shiffman, 1994), experience sampling (Feldman Barrett & Barrett, 2001; Scollon, Kim-Prieto, & Diener, 2003), and diary methods (Bolger, Davis, & Rafaeli, 2001) yield relatively large numbers of subjects and observations per subject, and data from such designs are sometimes referred to as intensive longitudinal data (Walls & Schafer, 2006). Analysis of EMA data using mixed models (also known as multilevel or hierarchical linear models) is well described by Schwartz and Stone (2007). Additionally, Moghaddam and Ferguson (2007) analyzed EMA data using mixed models to examine smoking-related changes in mood. These articles focus on the effects of covariates, either subject-varying or time-varying, on the EMA mean responses. Here we extend this approach by examining the degree to which covariates influence the within-subjects variation inherent in the EMA data.