ties, we can potentially lay claim to a commonality of results. Additionally, we want to point out that with any analysis a trade-off exists between aggregation problems (variation within the regions of analysis) and the availability of data (the finer the resolution, the lower the availability of region- specific data). The geopolitical units selected for our analysis are large enough to include the effects of hazards yet small enough to record significant socioeconomic variation, 10 and they can generate sufficient data sources to operationalize and test the model in Equation 2.5.
Third, most of the existing research has examined too few environmental threats; in other words, these studies have utilized too few dependent variables. Just because there is evidence of a relationship between toxic exposure of a single type (e.g., Superfund sites) and minority populations or the poor, that finding says nothing about the multitude of other kinds of toxic exposures and minority populations and the poor, such as water pollution and air pollution of varying types.
By the same token, the available research has been limited by the number of independent variables used in the analyses. Most environmental injustice research used models based on Equations 2.1-2.3. Many other measures besides race, class, and mobilization--as suggested by the environmental politics literature--could have been used as independent variables. We discuss these variables in Chapter 4.
Finally, most of the previous research has been limited to a single unit of analysis (e.g., state, county, city, ZIP code, SMSA), when what is needed is multiple analyses at several different levels. Finding evidence of environmental injustice at the county level says nothing about the relationship between toxic exposures, race, class, and mobilization at other levels of analysis, such as states and cities.
Given the conceptual and methodological problems in existing literature, the question arises as to how, without substantial scientific proof of the existence of race- or class-based inequities, did environmental justice surface onto the public agenda as a major public policy issue during the early 1990s? Moreover, why did the Clinton administration decide to vigorously pursue this issue when previous administrations (from Richard Nixon to George Bush) looked upon this issue as one that needed additional research before policies were put into place? Chapter 3 is devoted to those questions.