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SIPP Introduction & History

SIPP’s Purpose

As the face of SIPP has changed over the years, the concept and purpose has remained the same. SIPP serves to collect source and amount data related to various types of income, labor force participation, social program participation and eligibility, and general demographic characteristics to measure the effectiveness of existing federal, state, and local programs. SIPP also serves to estimate future costs and coverage for government programs and to provide improved statistics on the distribution of income and measures of economic well-being in the country.  

The main objective of the SIPP has been, and continues to be, to provide accurate and comprehensive information about the income and program participation of individuals and households in the United States. The survey’s mission is to provide a nationally representative sample for evaluating: 1) annual and sub-annual income dynamics; 2) movements into and out of government transfer programs; 3) family and social context of individuals and households; and 4) interactions among these items. A major use of the SIPP has been to evaluate the use of and eligibility for government programs and to analyze the impacts of modifications to those programs. The re-engineering of SIPP pursues these objectives in the context of several goals; including cost reduction, improved accuracy, increased relevance and timeliness, reduced burden on Survey Participants, and increased accessibility. The 2014 SIPP Panel will collect detailed information on cash and non-cash income (including participation in government transfer programs) once per year, from 1983-2013 interviews were conducted at 4 month intervals.

Survey Design and Sample Size

The SIPP survey design is a continuous series of national panels, with sample size ranging from approximately 14,000 to 52,000 interviewed households. The duration of each panel ranges from 2 ½ years to 4 years. The SIPP sample is a multistage-stratified sample of the U.S. civilian non-institutionalized population. From 1984-1993, a new panel of households was introduced each year in February. A 4-year 1996 Panel was implemented in April 1996; however, a 3-year panel that was started in February 2000 was cancelled after 8 months due to budget restrictions. Consequently, a 3-year panel was introduced in February 2001. The 2 ½ year 2004 SIPP Panel was started in February 2004 and was the first SIPP panel to use the 2000 decennial-based redesign of the sample. The 2014 Panel, starting in February of 2014, is the first SIPP panel to use the 2010 decennial as the basis for its sample. 

The SIPP content through the end of the 2008 Panel centered around a "core" of labor force, program participation, and income questions designed to measure the economic situation of people in the United States. These core questions expanded the data currently available on the distribution of cash and noncash income and repeated during each wave of interviewing. The survey used a 4-month recall period, with approximately the same number of interviews being conducted in each month or “wave” of the 4-month period. Interviews for all SIPP panels are conducted by personal visit and by decentralized telephone.  

The survey was also designed  to provide a broader context for analysis by adding questions on a variety of topics not covered in the core section. These questions were labeled "topical modules" and assigned to particular interviewing waves of the survey. Topics covered by the modules include personal history, child care, wealth, program eligibility, child support, utilization and cost of health care, disability, school enrollment, taxes, and annual income.

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Eligible Survey Participants

All household members age 15 years and older are interviewed by self-response, if possible; proxy response is permitted when household members are not available for interviewing.

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Sponsoring Agency and Legal Authority

The U.S. Census Bureau sponsors the survey under the authority of Title 13, United States Code, Section 182. This law protects all Survey Participants and their privacy.

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Release of Results

Data are released periodically in cross-sectional, topical module (through 2008 Panel), and longitudinal reports. These files are available currently for all waves of the 1984 through 1993 Panels, all waves of the 1996, 2001, and 2004 Panels, and for waves 1-13 of the 2008 Panel, which is scheduled to end in December 2013. Topical module files containing core and topical module data also are available for the 1984 through 1988 Panels, 1990 through 1993 Panels, the 1996, 2001, 2004 Panels and waves 1-11 of the 2008 Panel. Longitudinal files are also available for the 1984 through 1993 Panels. Longitudinal files for all waves of the 1996, 2001, 2004 Panels, and for the 2008 Panel for calendar years 2009 through 2011.

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Historical Background

Before SIPP

Until the advent of SIPP, the major source of data on income and program participation was the Current Population Survey’s (CPS) March Income Supplement. The CPS continues to be the source of all official income and poverty statistics published by the Census Bureau. However, the CPS is designed primarily to obtain information on employment. Because income measurement was never the primary purpose of the CPS, it has certain gaps in that area. The CPS does not capture the impact of changes in household composition during the year, nor does the survey explicitly measure periods of program participation. Additionally, the CPS does not collect data on assets and liabilities, which are needed to more completely measure a household’s economic status and eligibility for program benefits. To add those items to the CPS questionnaire would dilute the main purpose of that survey and unduly increase Survey Participant burden. Finally, the CPS is designed to be a cross-sectional survey. During the 1970s, the increasing size of government programs and their interactions with the labor market led to a need for longitudinal data.

To address those data issues, the Department of Health, Education, and Welfare (HEW) initiated the Income Survey Development Program (ISDP) in the late 1970s. In developing ISDP content and procedures, HEW focused on questionnaire length, length of reference period, and linkage of survey data to program records. The 1979 ISDP Panel was a longitudinal survey in which Survey Participants were asked about their income, labor force participation, and other characteristics. Survey Participants were then re-contacted every 3 months to supply information on themselves and others with whom they resided; consequently, the 3-month span was the reference period for the interview.

Creation and Evolution of SIPP 

The lessons learned from ISDP were incorporated into the initial design of SIPP, which was used for the first 10 years of the survey. The original design of SIPP called for a nationally representative sample of individuals 15 years of age and older to be selected in households in the civilian non-institutionalized population. Those individuals, along with others who subsequently lived with them, were to be interviewed once every 4 months over a 32-month period. To ease field procedures and spread the work evenly over the 4-month reference period for the interviewers, the Census Bureau randomly divided each panel into four rotation groups. Each rotation group was interviewed in a separate month. Four rotation groups thus constituted one cycle, called a wave, of interviewing for the entire panel. At each interview, surve participants were asked to provide information covering the 4 months since the previous interview. The first sample, the 1984 Panel, began interviews in October 1983 with a sample of 19,878 households. The second sample, the 1985 Panel, began in February 1985. Subsequent panels began in February of each calendar year, resulting in concurrent administration of the survey in multiple panels.  

The original goal was to have each panel cover eight waves. However, a number of panels were terminated early because of insufficient funding. For example, the 1988 Panel had six waves; the 1989 Panel, part of which was folded into the 1990 Panel, was halted after three waves. The intent was for each SIPP panel to have an initial sample size of 20,000 households; however, due to budget issues that target was rarely achieved.

As part of a SIPP redesigning effort, the 1992 Panel was extended to ten waves and the 1993 Panel was extended to nine waves. SIPP did not introduce new panels in 1994 and 1995. Before the redesigned SIPP questionnaire was introduced in the 1996 Panel, a dress rehearsal was conducted between February 1995 and September 1995. The dress rehearsal consisted of Wave 1 and Wave 2 interviews in approximately 9,000 households.

The 1996 Redesign

In 1990, the Census Bureau asked the Committee on National Statistics (CNSTAT) at the National Research Council to undertake a comprehensive review of SIPP. The resulting report, The Future of the Survey of Income and Program Participation (Citro and Kalton, 1993), summarized the first 9 years of SIPP and provided recommendations for the future of the survey. Some of those recommendations were implemented with the 1996 SIPP Panel in what is known as the 1996 redesign. 

One of the goals of the 1996 redesign was to improve the quality of longitudinal estimates in order to provide better information for policy makers. Specific changes include the following: 

  • A larger initial sample than in previous panels, with a target of 37,000 households;  
  • A single 4-year panel instead of overlapping 32-month panels;  
  • Twelve or thirteen waves instead of eight;  
  • The introduction of computer-assisted interviewing (CAI), which, among other improvements, permitted automatic consistency checks of reported data during the interview. Those checks reduced the level of post-collection edits and imputation and thus helped to maintain longitudinal consistency; and  
  • Oversampling of households from areas with high poverty concentrations. 

The first interviews of the redesigned SIPP began in April 1996 with the 1996 Panel. Later in 1996, Congress passed the Personal Responsibility and Work Opportunity Reconciliation Act (PRWORA). That law significantly altered the nature of public transfer programs, shifting more responsibility to state governments, establishing new eligibility rules for a number of programs, and setting limits on who could receive benefits. The existing welfare program, Aid to Families with Dependent Children (AFDC), was replaced with a new program, Temporary Assistance for Needy Families (TANF). Those changes came after interviewing for the 1996 Panel had already begun with a questionnaire designed for the array of transfer programs that existed before PRWORA was enacted. To accommodate program changes brought about by PRWORA, the Census Bureau began adapting transfer-program questions to reflect the current situation.

Continuous Improvement

In 1996, the SIPP Executive Committee established the Continuous Instrument Improvement Group (CIIG), consisting of staff from numerous divisions, whose task was to review and improve the SIPP core instrument. The CIIG generated an extensive set of recommendations including the need for thorough and rigorous testing, which led to the creation of a methods panel separate from the production survey. The methods panel project consisted of a small survey separate from the SIPP 2001 panel, which was experimentally designed to support rigorous testing of new alternative instrumentation. Testing took place between 1999 and 2003, including three field tests in 2000, 2001, and 2002. Field tests included a test instrument (consisting of CIIG's recommendations) and a control instrument (the SIPP 2001 production instrument). Results were then compared and analyzed, and the final instruments were delivered for implementation in the 2004 Panel.  

The 2014 Redesign

The 2014 SIPP Panel began in February 2014 with a sample of approximately 53,000 households based on the 2010 decennial census.  Each household was interviewed four times. Households were interviewed once a year with the new SIPP Event History Calendar (EHC), as compared to three times a year in previous SIPP panels. 

Previously, SIPP was molded around a central "core" of labor force and income questions supplemented with questions designed to address specific needs in complementary subject areas. The 2014 SIPP Panel design did not contain freestanding topical modules; however, a portion of traditional SIPP topical module content was integrated into the main body of the SIPP interview. Examples of 2014 SIPP content includes questions on medical expenses, child care, retirement and pension plan coverage, marital history, adult and child well-being, and others. The 2014 SIPP Panel used an EHC to assist the Survey Participant’s ability to recall events accurately over the longer reference period, and provide increased data quality and inter-topic consistency for dates reported by Survey Participants.

The 2014 SIPP Panel followed adults (ages 15 years and older) who move from prior wave households. Also, subsequent interviews increasingly incorporated dependent data, which is information collected from the prior wave interview brought forward to the current interview.

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