ABSTRACT
In this chapter we illustrate fitting linear mixed models (LMMs) to clustered longitudinal data, in which units of analysis are nested within clusters, and repeated measures are collected on the units of analysis over time. Each cluster may have a different number of units of analysis, and the time points at which the dependent variable is measured can differ for each unit of analysis. Such data sets can be considered to have three levels. Level 3 represents the clusters of units, Level 2 the units of analysis, and Level 1 represents the longitudinal (repeated) measures made over time.
