Invited Commentary: Considerations about Specificity of Associations, Causal Pathways, and Heterogeneity in Multilevel Thinking

During the past decade, there has been a dramatic increase in the use of multilevel modeling in epidemiologic analysis. There were 10 times as many papers in Index Medicus identified by the terms “multilevel” and “epidemiology” in 2005 than there were in 1995. In recent years, the American Journal of Epidemiology has published papers that use multilevel analyses to consider the associations between group-level characteristics and a range of health indicators (1–7). Accompanying these content-specific contributions have been several discussions of the strengths and limitations of multilevel modeling techniques (8, 9) and the rationale for applying these methods to public health (10, 11).