Each of the eight broad variables shown in Figure 1 can be unpacked and then further unpacked into multiple conceptual tiers. How far down or up a conceptual hierarchy a researcher needs to proceed depends on the specific empirical or policy question under investigation. Further, many interactions and outcomes depend on the specific combination of several variables at one or multiple tiers. The direction and strength of impact of one variable frequently depend on the combination of other variables present as well as the past history of processes in the SES.