The CHAS special tabulation is a count of the number of households (or housing units) that have certain combinations of HUD-specified characteristics, summarized for HUD-specified geographies.
2005-2009 CHAS (released January 2012):
For the data dictionary for the 2005-2009 data, click here: Data Dictionary 05-09.
2006-2008 CHAS (released December 2010):
For the data dictionary for the 2006-2008 data, click here: Data Dictionary 06-08.
2005-2007 CHAS (released December 2009):
For the data dictionary for the 2005-2007 data, click here: Data Dictionary 05-07.
Underlying Data:
The American Community Survey (ACS), from which the CHAS are now derived, has a smaller sample size than the Decennial Census (which was the basis of the 2000 CHAS). As a result, the Census Bureau cannot produce data using only one year of survey responses, except in very populous areas. For areas with population 65,000 or greater, ACS estimates are available each year using only the most recent year’s survey responses (known as "1-year data"). For areas with population 20,000 or greater, ACS estimates are available each year based on averages of the previous three years of survey responses ("3-year data"). For areas with population less than 20,000—including all census tracts, and many places, counties, and minor civil divisions—the only ACS estimates available are based on averages of the previous five years of survey responses ("5-year data").
HUD can purchase special tabulations of 1-year data, 3-year data, or 5-year data, subject to the same population thresholds. In 2009 and 2010, HUD only requested a special tabulation of 3-year data (2005-07 and 2006-08). In 2011, HUD requested a special tabulation of 5-year data (2005-2009). In future years, HUD expects to rotate to balance the timeliness of the data and its geographic precision.
Available Geographies:
HUD has obtained, or will obtain, the CHAS tabulations at the following geographic summary levels:
- 040 = State
- 050 = State - County
- 060 = State - County - County Subdivision
- 070 = State - County - County Subdivision - Place/Remainder
- 080 = State - County - County Subdivision - Place/Remainder - Tract
- 155 = State - Place - County
- 160 = State - Place
- 170 = State - Consolidated City
These are census definitions, which may be different than terminology used at the local level. For instance, St. Louis city and Baltimore city are treated as counties by the Census Bureau, and are geographically exclusive of their surrounding counties. Minor civil divisions are a census term for cities in certain states, while "place" is the Census designation for the vast majority of cities. For instance, Chicago is both a place and a minor civil division within Cook County; the CHAS data for Cook County includes Chicago households, but Chicago's data can be separately viewed in the MCD files or place files.
Other issues:
As with the CHAS 2000, rounding rules applied to all special tabulation data. This causes discrepancies when adding up smaller geographies. It has a similar effect when creating your own subtotals within a table. As a result, HUD recommends using the largest geographies possible, and the fewest number of table dimensions possible. In addition, the ACS can have very large margins of error, particularly with cross-tabulated data such as the CHAS. HUD realizes that some in some jurisdictions, for certain data elements, the ACS data may show unexpected results.
More explanation of Census geography is available here: Understanding Census Bureau Geography.
