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Learning about CHAS data: An Interview with Paul Joice

In this column, Paul Joice, Social Science Analyst with PD&R, talks about the Comprehensive Housing Affordability Strategy (CHAS) data.

Photograph of two multi-story single family homes along a street in the Woodlawn neighborhood of Chicago, Illinois.
CHAS data allow local recipients of CDBG and HOME program funds to determine how many low-income or extremely low-income households reside within a city, county, or census-designated place. Credit: Eric Allix Rogers, Creative Commons.

1. What is CHAS, and how did it come about?

In the early 1990s, HUD began to require grantees receiving Community Development Block Grant and HOME program funds to develop a Comprehensive Housing Affordability Strategy (CHAS). Although the CHAS regulations have long since been superseded by the Consolidated Planning process, CHAS data live on as an important source of information for assessing local housing needs. CHAS data have been produced by HUD and the U.S. Census Bureau from the 1990 census, the 2000 census, and more recently from the American Community Survey (ACS). Today, grantees continue to use CHAS data to decide how to use funds through important programs from HUD's Office of Community Planning and Development.

2. How are CHAS data compiled?

CHAS data are produced through a partnership between HUD and the Census Bureau. HUD provides the income limits that determine eligibility for HUD programs. Income limits vary; they are much higher in Washington, DC, than they are in Birmingham, Alabama. So the Census Bureau matches the income limit for each county, township, or metropolitan area with the corresponding ACS responses, which include information on household income, household size, housing cost, and many other key housing characteristics.

3. What information does the CHAS data set offer that the ACS does not?

The main thing that makes CHAS data unique is the addition of HUD income limits, which allows us to see how each household's income (based on the ACS) compares with the income limit for their city and to say how many households meet HUD definitions such as "low-income" or "extremely low-income." This information is also combined with other ACS variables. For example, whereas the ACS tells us how many renter households pay 50 percent of their income for rent, CHAS data tell us how many extremely low-income renter households pay 50 percent of their income for rent. CHAS data also include a custom variable that estimates affordability for a particular unit (regardless of the income of the household currently living there); this allows for the analysis of an important concept called "affordability mismatch." Finally, CHAS data allow us to combine variables that the Census Bureau does not combine in their standard ACS data products, such as the table that combines family status, tenure, and persons per room to estimate households at risk of homelessness.

4. How often are CHAS data updated and why?

Now that the Census Bureau is releasing ACS data every year, HUD is updating CHAS data every year as well. With ACS 5-year estimates, CHAS data should not change substantially from one year to the next. But because grantees across the country have different schedules for their Consolidated Plans, we want to provide them with the most recent data possible.

5. There seem to be two ways one can access the data: through the data download tool or by using the Query Tool/Table Generator. Please tell us more about these two methods.

When HUD receives CHAS data from the Census Bureau, we receive dozens of very large data files with thousands of records and hundreds of variables. Initially, after adapting the CHAS to rely on the ACS, these data files were the only way HUD provided CHAS data. But information in this format can be very difficult to work with, so we explored other ways to make the data more accessible. Our biggest breakthrough is the CPD Maps tool, which was initially released in 2012. This easy-to-use online mapping tool comes preloaded with key variables from the CHAS data and much more. Users can download reports with the data, or they can create custom maps. Another recent development is the CHAS Query Tool. Users can use simple drop-down menus to select the geography of interest and get a prepackaged set of tables, including some of the most commonly used indicators available from the CHAS data. Of course, more ambitious analysts can still download the full files to unlock the full potential of the CHAS.