8. A Graphical Introduction
One of the main attractions of multilevel models for public health research is their ability to allow relationships to vary across different contextual settings.
We illustrate this with a two-level structure consisting of individuals at level-1 nested within neighborhoods at level-2 with a single continuous outcome (e.g., poor health score) and a single continuous individual (compositional) predictor (e.g., age) centered about its mean.
illustrates a range of hypothetical graphical models for representing this data structure. In Figure 5(a), the poor health/age relationship is shown as a straight line with a positive slope: older people generally have poorer health. This model conceptualizes health status only in terms of an individual’s age, and the neighborhood context is ignored.