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Census.govPopulation Income Main Income MethodologyGuidance about Income Sources › Background

Guidance on Survey differences in Income and Poverty Estimates - Background

The Annual Social and Economic Supplement to the Current Population Survey (CPS ASEC) is designed to give annual, calendar-year, national estimates of income and official poverty numbers and rates. It is, nonetheless, used for many other purposes, including the allocation of federal funding.

The CPS is primarily a labor force survey, not an income survey, and is conducted every month by the Census Bureau for the Bureau of Labor Statistics using Computer-Assisted Telephone Interviewing (CATI) and Computer-Assisted Personal Interviewing (CAPI). The Basic CPS is used to calculate the monthly unemployment rate estimates. Supplements are added in most months; the ASEC is conducted in February, March, and April with a sample of about 100,000 addresses per year. The questionnaire asks about income from more than 50 sources and records up to 27 different income amounts, including receipt of numerous noncash benefits, such as Supplemental Nutrition Assistance (formerly known as the food stamp program), subsidized school lunches, and housing assistance.

The American Community Survey (ACS), replaced the decennial census long-form sample questionnaire. The ACS offers broad, comprehensive information on social, economic, and housing data and is designed to provide this information at many levels of geography. During the 2000-2004 testing program, the ACS collected income data for a much larger sample than the CPS ASEC (about 800,000 addresses per year). Beginning in 2005, the ACS sample size grew to about 3 million addresses. As with the decennial census long form, the ACS relies heavily on questionnaire responses mailed in by respondents. These estimates are collected on a rolling basis every month throughout the year, and the questionnaire asks about eight types of income received in the previous 12 months. For example, those interviewed in January 2010 were asked about income received in the January to December 2009 period, and those interviewed in December 2009 were asked about the December 2008 to November 2009 period.

There are many differences between the ACS and the CPS ASEC. Some of the most significant are:

  • The ACS uses an up-to-date sampling frame (the Census Bureau’s Master Address File updated by using the U.S. Postal Service’s Delivery Sequence File and targeted address canvassing). The CPS ASEC uses the Census 2000 sampling frame (updated with new construction since April 2000). Evaluations by separate updating operations are underway, but overall coverage for the ACS and the CPS ASEC appear to comparable.
  • The ACS data collection methodology is substantially different from the CPS ASEC, as the CPS ASEC is conducted by interviewers via CATI or CAPI. In contrast, the ACS uses a self-response mail-out/mail-back questionnaire, followed by CATI or CAPI follow-up conducted by interviewers. Additionally, the ACS, like the decennial long form, is mandatory, and therefore response at the unit and item level is higher in the ACS than the CPS ASEC.
  • The income questions in the ACS cover the major income sources, while the CPS ASEC income questions are much more detailed and provide a more comprehensive coverage of all potential income sources.
  • The calendar time period differs for ACS income estimates from those from the CPS ASEC and Census 2000, as the latter two use the previous calendar year while the ACS questions ask about income in the previous twelve months.
  • Until 2006 the ACS had excluded group quarters from its sampling frame, slightly affecting the estimates of income and poverty, as some people in the poverty universe are in noninstitutional group quarters, such as those in group homes and shelters. The ACS began including both institutional and noninstitutional group quarters in its sampling frame starting in January 2006 while the CPS ASEC includes only noninstitutional group quarters.

Data on income are also released periodically from the Survey of Income and Program Participation (SIPP), a longitudinal survey designed to track changes in income over time for the same households. Whereas the CPS ASEC is a labor force survey with supplementary questions on income, the SIPP focuses on income and typically reports more income (and therefore lower poverty) than the CPS ASEC. The SIPP consists of 9 or 12 interviews spaced 4 months apart over a 3- or 4-year period and asks a set of "core" questions about the previous 4 months by telephone and personal visit. Interviewers return to the same household (not housing unit) and attempt to follow each individual interviewed in the first series of interviews, even if they move. About 62,000 addresses were in the initial sample for the 2004 SIPP.

The SIPP is useful mainly for examining the changes in income (and poverty) for particular households and individuals over a 3- or 4-year period or for time periods shorter than a year, since it collects monthly income by source using a much more detailed questionnaire than the CPS ASEC – up to 81 sources of income and up to 73 individual income values.

The SIPP also contains information on many other subject areas that are critical for understanding social and economic well-being. These areas include wealth, disability status, health insurance coverage, child support, pension coverage, and measures of material well-being. The richness of this survey, coupled with its collection of high-quality income data, make the SIPP a unique and extremely valuable federal survey. Its estimates have been used to understand the relationship between job loss and health insurance coverage, to understand the employment of former welfare recipients, to estimate housing affordability, to understand the economic well-being of the disabled, and in many other policy-relevant analyses.

The Census 2000 long form used a mail-out/mail-back questionnaire that was very similar that used by the ACS (asking about eight income types). However, Census 2000 used only personal-visit follow-up using paper questionnaires while the ACS uses CATI, CAPI, and other methods to improve data quality. The estimates from Census 2000 are becoming more and more outdated as time passes, but that is all that is available for census tracts until ACS results are available in 2010.

The Small Area Income and Poverty Estimates (SAIPE) program was created by the U.S. Census Bureau, with support from other Federal agencies, to provide estimates of selected income and poverty statistics for states, counties, and school districts. The main objective of this program is to provide updated estimates of income and poverty statistics for the administration of federal programs and the allocation of federal funds to local jurisdictions. Beginning with the estimates for 2005, data from the ACS are used in the estimation procedure; all prior year estimates used data from the CPS ASEC. Estimates are produced annually.

The SAIPE program "borrows strength" from multiple data sources, including administrative records and multiple household surveys, to produce estimates with lower variance than estimates from any one source, but they are available a year later than the annual estimates from the CPS ASEC. The SAIPE program uses statistical methods to improve subnational estimates of income and poverty by using information from a variety of sources, including current surveys, population estimates, and administrative records such as aggregate food stamps and aggregate adjusted gross income from tax returns. Although used for critical purposes, such as in the funding formula that is used to distribute about $14 billion dollars a year to school districts under the Department of Education’s Title I Program, such information is provided only as a characteristics of a specific geographic area. A significant advantage of household surveys is their ability to allow analysis of how income varies along with other household and individual characteristics, such as nativity and work experience.


Source: U.S. Census Bureau | Income |  Last Revised: September 13, 2011