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New Mexico Small Areas

New Mexico Small Areas are 108 geographic areas across the state with population sizes that are just large enough to calculate rates for selected health events (e.g., diabetes deaths, asthma hospitalization, etc.). New Mexico small areas were based on population size, not land area. Most (95%) of the New Mexico small areas range in population size from 9,000 to 30,000 persons. Some counties have multiple small areas (Bernalillo County has 34 small areas within its boundaries). In other cases, entire counties (e.g., Harding, Quay and De Baca Counties) were combined to create a single small area.

Reporting of health data for New Mexico sub-state geographies has formerly consisted of presentation of data at the county level. County-level presentation is problematic in New Mexico because of the large differences in county population sizes. Smaller counties such as Harding and DeBaca (with 2010 U.S. Census estimated population sizes of 695 and 2,022, respectively)1, have unstable rates on most health measures, while health measures calculated for Bernalillo County (2010 Census population estimate=662,564) lack meaning because the population is large and diverse.

The New Mexico Department of Health (NMDOH) decision to embark on the small area project was based on the intense demand for health status information at the community level,2 the desire to study the associations between health inequity and place, and the belief that a standard set of small areas would improve efficiency in production of community data reports and accumulation of comparable community-level data across various public health indicators and datasets.

Contents
Methodology
Small Area Reference Materials
Geocoding and Classification of Data to Small Areas
Population Estimates
Small Area Workgroup
References


Methodology


From May of 2009 through November 2011, a workgroup consisting of staff from NMDOH, UNM, and others has met to design a set of New Mexico "Small Areas" for data reporting. The following design criteria were developed and used by the group.

Table 1. Criteria for Design of New Mexico Small Areas

  1. Areas should allow calculation of stable rates. To achieve stability in the rates, a target minimum population of 10,000 was set (yielding a denominator of at least 50,000 person-years across five years).
  2. NM small area geographies should be meaningful to communities. Small area boundaries should follow community boundaries whenever possible, and small areas should be as small as possible. A target maximum population size was set at 30,000.
  3. NM small areas will have within-area homogeneity and between-area heterogeneity on health-relevant demographic characteristics (given that criterion #2 is met). The demographic characteristics considered were(3):
    • Percentage of persons of Hispanic origin
    • Percentage of persons age 65+
    • Percentage of persons with a 4-year college degree
    • Percentage of children under age 17 in poverty
    • Percentage of owner-occupied housing units
  4. Numerators and denominators must be available at the census tract level to support the calculation of mortality and other rates. Small areas will be designed by combining census tracts.
  5. Absent other relevant considerations, a single area will not cross health region or county boundaries.

    6. Considerations for Presentation of Data by Small Areas:

  6. Adhere to the New Mexico DOH small numbers rules (to protect privacy).
  7. Combine up to five years of data to improve reliability of the estimates.
  8. Consider and communicate the likely impact of geocoding of numerator events to geographic features other than a complete, correct address.

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The New Mexico "Small Areas" Workgroup reviewed research and considered methods for defining small areas. All methods have advantages and disadvantages. For instance, ZIP code boundaries are relatively easy to communicate, but the boundaries shift over time and commercial marketing firms must be relied on to provide estimates of population size and other demographic characteristics.

The group decided to develop the New Mexico Small Areas by aggregating census tracts using above criteria as a guide. In the 2010 decennial census, New Mexico has 499 reporting census tracts with an average population size of 4,127. All but two NM Small Areas (4) were defined by combining adjacent census tracts. Demographic characteristics from the 2000 U.S. Decennial Census were examined to meet criterion #3.

The process yielded 108 New Mexico small areas with population sizes ranging from 929 (Area 99, Santa Fe County, State Penitentiary)(5) to 31,925 (Area 35, Chaves County, Roswell, N.E.). The area average population size is 18,892, and the median is 17,982. Many of New Mexico's more urban counties had sufficient population to support multiple sub-county small areas. In rural areas of the state, all or parts of two or more counties were often combined to reach the minimum population target of 10,000. Five New Mexico counties, Cibola, Torrance, Socorro, Lincoln, and Luna counties, were designated as single-county small areas.


Small Area Reference Materials

New Mexico Small Area Boundaries and Locations Map


New Mexico Small Area Map



Small Area Population Files


Small Area Mapping Resources

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A decision was made to avoid using tribal geographies as a design factor in the 108 small areas. That decision was based on the following considerations, 1) it is NMDOH policy to release tribal health data and results of analysis identified by tribe to only the tribe, and not release them publicly, 2) New Mexico census tracts did not always follow tribal area boundaries, and 3) the NMDOH tribal epidemiologist is able to provide tribes with tribe-specific data and analysis of results.



Classification of Data Records to Small Areas


Health event counts for a given New Mexico Small Area were derived by attempting to geocode the residential address of each decedent. Geocoding assigned each address an x and y coordinate that corresponded to the Earth's latitude and longitude. The accuracy and precision of the geocoding process depended on having a complete and correct address on every death certificate that could be matched uniquely to a standardized address in a geodatabase that provided the needed geographic coordinates. Death records such as P.O boxes or rural routes that could not be matched to a standardized address were geocoded with the most precise alternate geocode available. Often this was the geocode of a nearby intersection, or the geographic centroid of the ZIP code, populated place, or county referenced in the address. Certain conditions make it difficult to precisely geocode every death record, including:
  • Missing or incorrect street numbers
  • Missing, misspelled, or nonstandard street names
  • Use of a post office box only
  • Use of a rural route, highway contract route or general delivery address


important! icon It is important to recognize that small areas with misclassified data records will yield calculated health event rates that are higher or lower than the actual rate in that area. The New Mexico Department of Health is currently evaluating the small area rates published on NM-IBIS for misclassification errors. Until that evaluation is complete, please use those rates with caution and include the following caveat along with any report of your results:

Locating a data record in a New Mexico Small Area required geocoding (assigning latitude and longitude to) the residential address for each health event (birth, death, cancer incidence, etc.). Sometimes health events, especially those with addresses such as P.O boxes or rural routes, could not be assigned to a small area. Excluding these records from the small area analysis introduces bias (underestimates of counts and rates) into the results. This was more likely to occur in rural areas of the state (where P.O. boxes and rural routes are more common), but may have occurred in any of the 109 small areas. For more information on the New Mexico Small Area Methodology, please visit the [[a href="/nmibis-view/resource/SmallAreaMethods.html" Small Area Methods]] page.

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Population Estimates


Computation of death rates for a small area requires a count of deaths (numerator) and a population estimate (denominator) for each area and time period. The use of U.S. Census tract boundaries to define our small areas was based in part on the need for consistent geographies in the numerator and denominator. Census tract population estimates by year, age, sex and race for 2010 U.S. Census geographies for the years 1990 to 2010 were calculated by the Geospatial and Population Studies program at the University of New Mexico. (For more information on calculation of health event rates, please see the NM-IBIS page on Health Event Rates.)


New Mexico Department of Health Small Area Workgroup


The New Mexico Small Area Workgroup met from May of 2009 through November 2011 to design the New Mexico Small Areas and Small Area Methodology.

Will Athas - UNM, Family & Community Medicine
Alexis Avery - DOH, PHD, Family Health Services Bureau
Jack Baker - UNM, Bureau of Business and Economic Research
Paige Best - DOH, ERD, Community Health Assessment Program
David Broudy - DOH, Metro/Northwest Health Region
Camille Clifford - DOH, Bureau of Vital Records and Health Statistics
Kate Daniel - DOH, Northeast Health Region
Janet Flores - DOH, Southwest Health Region
Lois Haggard - DOH, ERD, Community Health Assessment Program
Corazon Halasan - DOH, PHD, Diabetes Program
Wayne Honey - DOH, ERD, Injury and Behavioral Epi Bureau, Survey Unit
Heidi Krapfl - DOH, ERD, Environmental Epi Bureau
Michael Landen - DOH, ERD
Tracey Luna - DOH, Southeast Health Region
Jerry Montoya - DOH, Metro/Northwest Health Region
Larry Nielsen - DOH, Bureau of Vital Records and Health Statistics
Srikanth Paladugu - Bernalillo County
Jim Roeber - DOH, Injury and Behavioral Epi Bureau, Substance Use Epidemiology Section
Tom Scharmen - DOH, Metro/Northwest Health Region
Karen Scherzinger - UNM, Institute for Public Health
Barbara Toth - DOH, ERD, Environmental Epi Bureau, EPHT Program



References


1. U.S. Census Population estimates downloaded from http://quickfacts.census.gov on 10/27/2011.

2. Bernalillo County Community Health Council: Health Data. Downloaded from http://www.berncohealthcouncil.org/health-data on 11/1/2011.

3. The five demographic characteristics were selected based on analysis performed by the Utah Department of Health suggesting that these characteristics were representative of a larger set of demographic characteristics that were strongly associated with a variety of health outcomes.

4. Area 9, Military bases, is spread across Bernalillo, Curry, Dona Ana, and Otero Counties. Area 93 is a bow-tie-shaped area in Santa Fe County that has two almost contiguous parts.

5. Area 100, Santa Fe County, State Penitentiary, is more of a "carve-out" to improve the representativeness of data for the surrounding area, 99 - Santa Fe County, South.

6. Scharmen, Thomas (2011) An Inventory of Address Variables in 18 Years of Birth and Death Records. Presented at the October 5, 2011 meeting of the New Mexico Department of Health Small Area Workgroup.




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