ATSDR Uses GIS and Demographics to Characterize Communities at Risk

Janet L. Heitgerd, PhD, ATSDR

The demographic characterization of a population living near a hazardous waste site provides ATSDR with essential information needed to assess and address public health issues in local communities. ATSDR uses this information to (a) estimate the size and demographic characteristics of the population that potentially has been exposed to hazardous substances, (b) identify sensitive populations in the area (e.g., children, childbearing-aged women, and the elderly), and (c) provide insight about the social context of the area.

The ability to link population and housing data to the geographic location (e.g., a point defined by longitude and latitude) of a hazardous waste site through geographic information system (GIS) technology improves ATSDR's capability to estimate current population numbers. This results in a more accurate characterization of site demographics in a shorter period of time. It also helps the agency to develop communication and health education efforts for the local community and to identify potential environmental justice issues at a site.

ATSDR relies principally on data from the U.S. Department of Commerce, Bureau of the Census, to characterize community demographics. Decennial census data are the most complete source of residential population information for the United States and its territories (e.g., Puerto Rico and the U.S. Virgin Islands). Demographic data are currently available from the 1990 census, and data from Census 2000 are expected to be released in spring 2001. The Bureau of the Census estimated that 248.7 million persons resided in the United States in 1990. By 2000, this estimate was expected to be more than 275 million.

Understanding the population distribution across the nation's landscape and using this information in a GIS requires knowledge of census geography (i.e., the political and statistical areas the Bureau of the Census uses to tabulate and report demographic data). Most U.S. residents know the country's geographic/political areas (e.g., states, counties, cities, and Native American reservations), but many are less familiar with the geographic/statistical areas developed by the Bureau of the Census, and which form the basis ATSDR uses to analyze and report population and housing data for small geographic areas (e.g., census tracts and census blocks) (Table 1) (1,2).

U.S. census data describing residential population and housing provide the most complete picture of our nation and its subareas. Basic population and housing data (e.g., age, race/ethnicity, and sex) are reported for all census geographic levels (e.g., state, city, census tract, and census block). Additional demographic data, including socioeconomic information, are available at the block group level and at the larger geographic levels (3).

ATSDR incorporates U.S. census population and housing data into a GIS application, which generates demographic maps for the areas near active hazardous waste sites (e.g., those listed by EPA on the National Priorities List). A map of each site contains the location of the site and its surrounding area (within a 1-mile buffer). Using an area-proportion spatial analysis technique in a GIS, demographic statistics from the 1990 census are calculated and the results listed in a site map. ATSDR also records these data in its HazDat database, which contains detailed site-specific information regarding hazardous waste sites. Through GATHER, a site map can be generated that contains these demographic statistics for any hazardous waste site in the comprehensive HazDat database.

GIS maps that overlay data on population, environmental contaminants, and health outcomes are produced routinely for hazardous waste sites. Requests by ATSDR staff for additional current and historical demographic data, such as housing age, length of residence, and socioeconomic status, are easily incorporated into the GIS system. ATSDR also provides GIS-generated demographic statistics in response to requests from other public health agencies, including CDC and the 28 state health departments that have cooperative agreements with ATSDR.

Demographic Data and Segmentation Systems

An issue in using census data to examine area demographics is that the data reflect the population and housing status of U.S. residents on April 1 of a census year (e.g., 1990, 2000), but area demographics can change over time, particularly in smaller geographic areas. Several companies use the most recently published census data to project current-year demographic estimates for the period between official censuses. These projections are then incorporated into a system that segments small geographic areas into categories reflecting the demographic characteristics, lifestyle, and consumer behavior patterns of residents.

To meet the agency's need for updated data statistics, ATSDR licenses with Claritas, Inc., for estimates of current-year demographic data at the block-group level. These data include age, race/ethnicity, sex, income, education, and housing. ATSDR uses the PRIZM segmentation system developed by Claritas, Inc., to obtain additional demographic and lifestyle information about populations living near hazardous waste sites (4). The concept behind the PRIZM segmentation system is that individuals are more likely to live near others who share similar demographic and behavioral characteristics. The PRIZM segmentation system divides the U.S. population into 62 neighborhood types, or "clusters," on the basis of residential location (i.e., geodemographics).

PRIZM has copyrighted names for each of the 62 neighborhood types (e.g., "Kids and Cul-de-Sacs" and "Southside City") that it assigns to census block groups, census tracts/block numbering areas, and zip codes. These neighborhood types can be used to analyze and display demographic data in a GIS. The cluster names are meant to catch interest and convey a general sense of the character of an area; however, they should not be interpreted literally. PRIZM contains demographic and market research data that define and differentiate each cluster. The marketing research data include information on lifestyle (e.g., smoking, gardening, and exercise), media habits (e.g., television, newspaper, and radio), financial product usage (e.g., health insurance information), and general product use (e.g., foods and alcohol).

Used successfully as a marketing tool for many years by the business industry, segmentation systems are increasingly used by public health agencies to (a) explore the relationship between community and disease, (b) target health interventions, and (c) develop communication strategies. For example, the Georgia Division of Public Health used cluster information to target mammography programs in factory towns designated as "Mines and Mills" because women in those communities had higher rates of breast cancer (5). The Office of Communication (OC) of the Centers for Disease Control and Prevention (CDC) collaborates with the centers that comprise CDC on projects that integrate PRIZM data with epidemiologic and other data for communication planning (6). One example of this collaborative work concerns prevention efforts for hantavirus. Using zip code information, OC and the National Center for Infectious Diseases (NCID) identified the PRIZM clusters at which 164 cases of hantavirus had been diagnosed in the United States during 1993 through 1997. Residents of these clusters then can be targeted as the priority audience to address for prevention messages about hantavirus (6).

Community Research

In support of ATSDR programs and initiatives (e.g., the Minority Health Program and the Child Health Initiative) to define the issues concerning hazardous substances and special populations, agency staff also use GIS technology and techniques to conduct demographic research on populations living near hazardous waste sites. This research helps ATSDR to understand the health status of these segments of the population. For example, if racial/ethnic minority groups and/or residents of areas designated as having lower socioeconomic status are more adversely affected by close proximity to hazardous waste sites, ATSDR must determine the implications for public health activities in these areas.

In 1995, ATSDR published an article in the International Journal of Occupational Medicine and Toxicology about a GIS approach used to analyze the 1990 racial and ethnic composition of the population near 1,200 National Priorities List sites (7). Approximately 11 million persons were found to live within a 1-mile buffer of these sites. ATSDR staff are updating this analysis using current-year demographic estimates for race/ethnicity and socioeconomic status and reviewing data for 1980-1999 to better understand the types of demographic changes that occur in areas near hazardous waste sites. Using the PRIZM segmentation system database, ATSDR is also studying the types of neighborhoods in which NPL sites are found. An initial analysis of the data suggest that a concentration of these sites exists in neighborhoods described as "Middle America," "Family Scramble," and "Military Quarters."

Creating Community Profiles

ATSDR is using a wide range of small-area demographic data to create community profiles as a logical first step in its public health activities for communities near hazardous waste sites. Data products from Census 2000 will provide up-to-date, small-area population and housing data. The 2000 TIGER/Line File, the digital database of U.S. geographic features developed by the Bureau of the Census, will include Census 2000 statistical area boundaries. Census 2000 and the 2000 TIGER/Line File are expected to be available in spring 2001. ATSDR plans to publish a report this fall on how the population changes reported in Census 2000 affect the agency's population analysis for areas near hazardous waste sites. Significant changes are not expected, except possibly in the reporting of race/ethnicity. Census 2000—for the first time—instructs individuals to check one or more categories on the form's race/ethnicity question. ATSDR will continue to refine its GIS-based applications for population estimation to produce more timely and accurate demographic data for communities located near hazardous waste sites.

References

1. Bureau of the Census. Census `90 basics. Washington (DC): U.S. Department of Commerce; 1990. Pub. No. CPH-I-8.

2. Bureau of the Census. 1990 Census of Population and Housing: Summary Tape File 3 Technical Documentation. Washington (DC): U.S. Department of Commerce; 1992.

3. Bureau of the Census. United States Census 2000; Uses for questions on the Census 2000 forms: Appendix B. Washington (DC): U.S. Department of Commerce; 1998. Available at http://www.census.gov/dmd/www/content.htm.

4. Claritas, Inc. PRIZM methodology. Arlington (VA): Claritas, Inc.; 1994.

5. Weiss MJ. The clustered world. Boston: Little, Brown and Company; 2000.

6. Pollard WE, Kirby SD. Geographic information systems (GIS), public health data, and syndicated market research data bases in health communication. Presented at the National Conference on Health Statistics; 1999 August 2-4, Washington, DC; 1999.

7. Heitgerd JL, Burg JR, Strickland HG. A geographic information systems approach to estimating and assessing National Priorities List site demographics: racial and Hispanic origin composition. Int J Occup Med Toxicol 1995;4(3):343-63.

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