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CHAS: Background

CHAS Background

The primary purpose of the CHAS data is to demonstrate the number of households in need of housing assistance. This is estimated by the number of households that have certain housing problems and have income low enough to qualify for HUD’s programs (primarily 30, 50, and 80 percent of median income). It is also important to consider the prevalence of housing problems among different types of households, such as the elderly, disabled, minorities, and different household types. The CHAS data provide counts of the numbers of households that fit these HUD-specified characteristics in HUD-specified geographic areas.

In addition to estimating low-income housing needs, the CHAS data contribute to a more comprehensive market analysis by documenting issues like lead paint risks, "affordability mismatch," and the interaction of affordability with variables like age of homes, number of bedrooms, and type of building.

Data Format

HUD has identified a large set of characteristics of interest to housing planners and policy-makers, and as a result the CHAS data can be quite unwieldy. To streamline the data and make it easier to use, HUD has created a series of "tables," which are grouped by theme.

Each of these tables contains certain "dimensions" (also referred to as variables). These dimensions can be combined in a number of ways, and the data files for each table present every possible combination of those dimensions. As an example, consider Table 11. Table 11 contains 3 dimensions: tenure, housing problems, and household income. Tenure has 2 options: owner-occupied or renter-occupied. Housing problems has 3 options: household has at least one housing problem, household has no housing problems, or household has no income (so cost burden could not be computed) but no other housing problems. Household income, in this particular table, has 13 options. Thus Table 11 essentially has 78 buckets (2*3*13=78), and every household belongs in one (and only one) of those buckets. In the CHAS data, we have counted the number of households in each of those buckets, for thousands of states, counties, cities, and neighborhoods.

Because CHAS provides count estimates, users interested in percentage estimates (e.g. percentage of low-income renters with severe housing cost burden) will need to make the calculation themselves. To make these calculations, users may need to sum count estimates (buckets) in both the numerator and denominator before dividing to obtain the percentage estimate. Users should be careful to identify the appropriate total or subtotal that serves as the denominator. In some cases, totals and subtotals are provided in the CHAS data.

Data Source & History

CHAS consists of “custom tabulations” of data from the U.S. Census Bureau that are generally not otherwise publicly available. Originally, CHAS estimates were drawn from decennial census data. HUD first obtained the CHAS data after the 1990 Census and again after the 2000 Census (available here: CHAS 2000 Data). Since 2005, the Census Bureau has administered an annual survey called the American Community Survey (ACS), which replaced the detailed survey portion of the decennial census. The ACS offers timely data for the period between censuses, allowing for a relatively current picture of local conditions. The transition from the Census long-form to the ACS forced HUD to revise the CHAS data, so the 1990 CHAS and 2000 CHAS differ in some important ways from the ACS-based CHAS data released in 2009 and later. For general information about comparing Census 2000 data to ACS data, see this guidance from the Census Bureau.

At various points, HUD has needed to revise CHAS data after public release to correct errors or improve usability. These changes have been logged on the CHAS Updates page, which also catalogs data releases and improvements to the web applications. Users should check Updates to insure that they are using the latest version of data.


A full data dictionary is provided (see here: Data Documentation), but is targeted to advanced users of the CHAS data working with the raw data files. This section defines some terms that may be unfamiliar to newer users of the CHAS or Census data:

HAMFI – HUD Area Median Family Income. This is the median family income calculated by HUD for each jurisdiction, in order to determine Fair Market Rents (FMRs) and income limits for HUD programs. HAMFI will not necessarily be the same as other calculations of median incomes (such as a simple Census number), due to a series of adjustments that are made (For full documentation of these adjustments, consult the HUD Income Limit Briefing Materials). If you see the terms "area median income" (AMI) or "median family income" (MFI) used in the CHAS, assume it refers to HAMFI.

Household – All people living in a housing unit. Members of a household can be related (see family) or unrelated.

Household Income – Adjusted household income, which includes the income of all members of the household at the time of the survey, adjusted for inflation to reflect the most recent year of the data release (e.g. 2013 dollars in the 2009-2013 CHAS data).

Family – Related individuals living in the same household. The Census Bureau also tracks subfamilies.

Housing Problems – There are four housing problems in the CHAS data: 1) housing unit lacks complete kitchen facilities; 2) housing unit lacks complete plumbing facilities; 3) household is overcrowded; and 4) household is cost burdened. A household is said to have a housing problem if they have any 1 or more of these 4 problems.

Overcrowding – More than 1 person per room.

Severe overcrowding – More than 1.5 persons per room.

Cost burden – Monthly housing costs (including utilities) exceeding 30% of monthly income.

Severe cost burden – Monthly housing costs (including utilities) exceeding 50% of monthly income.

Elderly – People aged 62 and up. Individuals age 75 and up are generally recognized as a population with different needs than those 62-74, so the CHAS data separates these groups. "Elderly" refers to individuals 62-74, while those 75 and up may be referred to as "extra elderly" or "frail elderly".

Disabled – In 2008, Census modified the ACS questions related to disability. Beginning with the 2008-2010 and 2008-2012 CHAS data, HUD has separately identified four different physical or cognitive limitations: hearing or vision impairment, ambulatory limitation, cognitive limitation, and independent living limitation.