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Show central and southern portions of the state having the highest percentages of uninsured persons, and urban and northern areas having the lowest percentages. Over 90% of Utah households obtained insurance coverage through an employer or union (Bureau of Surveillance and Analysis) suggesting that differences in the types of jobs and industries predominant in a given area may be an important cause of the observed pattern. Cigarette Smoking The overall adult cigarette smoking rate reported by the 1996 Utah Health Status Survey was 12.3%. Smoking rates ranged from 0.1% in South Jordan (#35) to 34.8% in Magna (#20) (Figure 5). The association in the 1996 Utah Health Status Survey data between smoking rates and LDS religion among the 61 small areas in Utah r = -.61, £ < .001) suggests that smoking behavior is strongly influenced by the LDS religion in Utah. However, membership in the LDS religion accounts for only 36% of the variance in cigarette smoking in Utah, suggesting that other correlates of cigarette smoking, such as education level or local cultural factors, are also important. Discussion The four health measures described in this paper offer examples of how small area analysis can be a useful tool for examining, describing, and exploring relationships among health variables in small areas. Three issues that warrant further discussion are 1) the method used to specify small area boundaries, 2) the use and interpretation of statistical techniques, and 3) the process of mapping itself. Difficulties with Designating Small Area Boundaries Using Existing Administrative Boundaries. One of the ongoing challenges to meaningful mapping of health information is that administrative boundaries designed for a particular purpose do not typically match boundaries that would be ideal for planning purposes (Kirby, 1996). Ideally, other boundaries should have been incorporated into this small area design, such as city boundaries, school district boundaries, and boundaries that signify neighborhood identities. Because ZIP code areas are arbitrary areas designed for the convenience of postal carriers, they often do not correspond to other, more meaningful boundaries, such as those of cities or towns, school districts, or political voting districts. They may also be heterogeneous with respect to relevant characteristics, such as socio-economic status. However, ZIP codes are found on most public health data records (e.g., birth, death, hospital discharge, etc.), they are routinely gathered or can easily be incorporated in survey and other data collection efforts, and population denominators and other demographic characteristics are often available for ZIP code areas. Regardless of how well small area boundaries match relevant community boundaries, they may not match boundaries of a particular health event. In such cases, the zone where the event (e.g., a disease or exposure) occurred will be divided between two or more small areas, diluting the observed rates and perhaps resulting in the pattern being missed altogether. However, there is a scientific argument for deriving a priori the small area boundaries independent of the geographic patterns of health events. Stability of Administrative Boundaries. An investigator who uses them does so with the understanding that they may change at any time, without regard for the investigator's needs. Areas such as U.S. Census Bureau block groups and ZIP code areas are subdivided as the populations within them increase. Although it is possible for an investigator to stay current with prospective changes to administrative boundaries, particular problems are encountered in retrospective application of a small area design. Small area boundaries may align with ZIP codes in the present, but a given ZIP code essentially either grows bigger or disappears as one goes back in time. An investigator must decide how methodologically to deal with ZIP code areas whose former boundaries spanned more than one current small area. Availability of Data for Administrative Areas. Area boundaries must also take into account the availability of data, such as population estimates. Valid population estimates are needed to calculate disease and mortality rates, and are not always easily obtained. Establishing Area Size. For some health measures, such as prenatal care, where rates are based on the almost 40,000 births each year in Utah, rates were precise enough that the areas could have been subdivided further into more geographic detail. That would satisfy the needs of those for whom areas, such as the large, multi-county areas, cover too much territory to provide meaningful local information. For other measures based on relatively rare events, such as lung cancer deaths, the small areas defined here were already too small, yielding imprecise estimates 22 |
