Invited Commentary 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 iden-tified by the terms ‘‘multilevel’ ’ and ‘‘epidemiology’ ’ in 2005 than there were in 1995. In recent years, the American Jour-nal 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). Accom-panying these content-specific contributions have been sev-eral discussions of the strengths and limitations of multilevel modeling techniques (8, 9) and the rationale for applying these methods to public health (10, 11). In this issue of the Journal, Wight et al. (12) examine whether neighborhood context influences the cognitive function of older adults. This paper contributes to the liter