We created a set of standards to identify a comparison community similar to the impact zone. We considered income levels and racial and ethnic composition of the population as well as environmental conditions such as distance from possible sources of pollution like landfills and oil wells. We selected comparison communities that are in or near Los Angeles County and demographically similar to the impact zone. We did not use comparison communities in areas further away because that would introduce environmental, social, and contextual variations that are not quantifiable and would restrict our ability to draw meaningful conclusions.