The paper under analysis characterizes the spatial point pattern of air toxics in the U.S. Environmental Protection Agency (EPA) designated Environmental Justice area of West Oak-land, California. Integrating a GIS framework and an interdisciplinary statistical technique called Ripley’s K-function, Fisher et al. verify the neighborhood as an environmental justice site across multiple spatial scales, and by means of an air dispersion model, identify the number of people potentially affected by a particular facility, and engage the problem of non-point sources of diesel emissions with an analysis of the street network (Fisher, 2003; Fisher et al, 2006). DATA SOURCES
The data used in this study was mainly obtained from two different sources: 1. US Census Bureau’s 2000 survey, referred to as census 2000, and spatially referenced by means of TIGER digital files.
2. Toxic Releases Inventory (TRI; volume and location of emissions from facilities). The census is a statistical method to collect data about every unit within a population or universe. The information does not need to be transformed to be statistically useful, unlike what happens with administrative data sources. The advantages and disadvantages of the census in comparison to other methods are commented below (based on Glejberman, 1997). Between the strengths:
* Total coverage of the population aimed (sampling variance is zero). *“Cross-tabulation of a wide range of demographic, social and economic data” (Vidler, 2001) *The results can be presented per administrative units or smaller classification criteria (national to local scale), thus the level of aggregation can be chosen. * The census represent a reference for countinous statistics, due to its periodical updates. * Allows the selection of samples and design of further studies. * The only procedure to investigate low-frequency events: detailed small sub-groups of the population are represented.
* Broad acceptance by the population, in general.
And with regard to the limitations of a census:
* High human and material costs.
* Wide organization needed that covers and controls the whole universe, avoiding omision and duplication of data.
* Delay in obtaining results.
* Response burden: every member of the target population needs to provide data * As a result, information obtained can be of lower precision/quality (due to a bigger error, both in data collection and processing) than if other sampling technique had been used. The Census 2000 has been acclaimed to be "the largest peacetime effort in the history of the United States", a motto made popular by the Bureau and widely spread through the media (see Edel 1999 as an example). The Bureau provides census tract boundary files (referred to small geographic areas with 2,500 to 8,000 inhabitants), containing demographic and socio- economic data for the entire nation. However, it is impossible to cover every person, and in the last decades, some cities have claimed that the mail questionnaire method results in an under-count of minorities. Different sampling techniques were proposed in order to adjust the final count (Pence, 1997). Eventually, it turned to become a political issue and by a parliamentary decision, the statistically obtained population were not finally reflected on the 2000 census. A criticism to the present study could certainly be that in additional to the decennial federal census, more localized versions could have been used, in order to obtain more accurate results. About Census Bureau Topographically Integrated Geographic Encoding and Referenc- ing System (TIGER) files, or the Tiger...