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The Approach to Updating the ZCTA-Level Demographic Data in the UDS Mapper Prior to the Release of the Official 2010 ZCTA Attributes

Background:

The transition between detailed, long-form, decennial census data and annual American Community Survey (ACS) data leaves 2011 as a bridge year. For ZIP Code Tabulation Areas (ZCTAs), certain demographic data such as income and poverty, will not be available until 2012 in the 2007-2011 ACS 5-year estimates. (See this link: https://askacs.census.gov/app/answers/detail/a_id/8803/kw/z5year/session/L3RpbWUvMTMwNjE3NTIyNC9zaWQvTmU4X0RIdWs%3D) As a result, it is not possible to update the ZCTA-based information in the UDS Mapper with directly-surveyed Census data for the next year and a half, despite the current availability of actual 2010 population counts at the block level and 2005-2009 ACS poverty data (which now serves as the Census basis for income and poverty rates).

One option to provide a much needed update to the population denominator data for the UDS Mapper is to apply ACS 2005-2009 demographic/income rates to Census 2010 Block populations using currently available 2010 Re-Districting data, and then re-aggregate that data to newly defined 2010 ZCTA areas based on Block centroids provided by Census. This would have the dual benefit of 1) providing updated poverty and income data for 2011 that would not otherwise be available and 2) provide the UDS Mapper with updated ZIP Code/ZCTA area geographies that will be ready to transition to actual ACS tabulations after the 2012 release.

JSI created these estimates using Geographic Information Systems (GIS) spatial tools to connect 2010 Census Block centroids with poverty and income data from American Community Survey 2009 5-year estimates, and then re-aggregated these data to the new 2010 ZCTA boundaries for use in the UDS Mapper.

Methods:

Datasets available for this process:
Using a spatial join in GIS, Census 2010 Block centroids were coded with Census 2000 Block Group and Tract FIPS ID numbers and 2010 ZCTA FIPS ID numbers. The ACS 2005-2009 data was tabulated using Census 2000 geographies. Block Group Income and poverty rates were assigned to each Block that fell within that Block Group and combined with the actual 2010 population counts to estimate the number of poor and low-income individuals in each block in 2010, controlling for the portion of the population for whom poverty has been determined. Note: due to Census Bureau errors in the 2005-2009 ACS, approximately 300 Block groups were tabulated using Census 2010 boundaries instead of the 2000 boundaries used in all other areas of the country. In these areas, tract-level ACS values for income and poverty were used instead of block groups, as that level was not impacted. Minority population values are available at the 2010 Block level and were used directly.

Once poverty/low-income population was calculated for the Block centroids, these values can be aggregated up to any other geography. Using a spatial join in GIS, each 2010 ZCTA area was summed with the block totals that fall inside its boundaries.

The final product provides updated poverty/low-income and minority values calculated for the new 2010 ZCTA boundaries. JSI also created a new ZIP Code-to-ZCTA crosswalk table to permit UDS user data reported by ZIP Code to be connected to the new 2010 ZCTA boundaries. JSI assures that comparisons to prior years of UDS data will remain valid by recalculating 2008 and 2009 data to the updated boundaries. JSI provided these data to be incorporated into the UDS Mapper for a major update to demographic, income and patient data.