SIPP Panels

A SIPP panel is a group of households selected to be interviewed periodically over multiple years. A panel may run alone, such as the 2014 Panel, or concurrently with other panels, such as the 1990 through 1993 Panels. Since 1984, there have been 17 SIPP panels total. Table 1-1 shows historical SIPP panels and the time periods in which their interviews were conducted.

The first SIPP panel, the 1984 Panel, began interviews in October 1983. 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. Because of budget constraints, actual panel duration has varied. SIPP’s original goal was to have panels of eight interviews covering 32 months. In several instances, due to budget and other issues, panels were terminated after seven interviews (28 months). Three panels were terminated even earlier: 1988 (six interviews), 1989 (three interviews), and 2000 (2 interviews). With certain exceptions, each panel overlapped part of the previous panel, with the result that there were two or three active panels at any given time. Overlapping panels allow data users to pool records from different panels, thus having larger samples (and lower standard errors) for cross-sectional analyses.  The overlapping feature of the SIPP design was dropped for the 1996 through 2014 Panels, but standard errors for non-overlapping panels remained small since at least 29,000 households were interviewed (considerably more than in the previous panels).

Like the 1990 through 1993 Panels, the 2018 Panels and beyond overlap with new panels that begin each subsequent year (2019, 2020, and so on). Figure 1 1 depicts this design. Although multiple panels are now collected during each annual interview cycle, they are referred to by their calendar year of collection (e.g., all panels collected in 2021 are collectively referred to as “2021 SIPP”). Like the 1990 through 1993 Panels, the 2018 Panels and beyond overlap with new panels that begin each subsequent year (2019, 2020, and so on). Figure 1-1 depicts this design. Although multiple panels are now collected during each annual interview cycle, they are referred to by their calendar year of collection (e.g., all panels collected in 2020 are collectively referred to as “2020 SIPP”). 

Waves

Within a panel, a full cycle of administering the questionnaire – i.e., conducting a round of interviews with the selected households – is a wave. The first time an interviewer contacts a household, for example, is Wave 1; the second time is Wave 2, and so forth.  Prior to the 2014 Panel, most SIPP panels consisted of between 8 and 16 waves. Because SIPP changed to interviewing annually instead of every 4 months, the 2014+ Panels consist only of 4 waves. There were 4 interviews for the 2014+ Panels instead of the 8 to 16 interviews in previous SIPP panels. As before, each round of interviews results in published public-use data files.

Reference Periods

Each interview wave has a corresponding reference period that most of the data represent. For the 2014+ SIPP, most interview questions ask about the preceding calendar year, and therefore these data in general refer to the previous calendar year. Notable exceptions to this are questions about disability status and parent-child relationships, which are asked as of the time of the interview. Prior to the 2014 Panel, the reference period for most interview questions was the preceding 4 months.  Annual interviews still provide key month-level data, however. For example, SIPP asks each respondent if he or she had a health insurance plan at any time between January 1 of the reference year and the time of interview. If the answer is yes, the event history calendar develops spell- and month-level data for the respondent’s coverage over each of the months in the reference period. Over the course of a 4-wave panel, data are collected and released covering 48 consecutive months.

Interview Procedures

Locating Sample Address and Respondents

During Wave 1 of a panel, the interviewer visits the sampled address, compiles a household roster, and attempts to interview all members of the household who are aged 15 years and older.  Information about household members under 15 years of age is collected via a proxy interview. Typically, a household member is someone who sleeps in the household the majority of the time. The SIPP instrument determines whether each person is a household member by asking a series of questions.

While the Census Bureau prefers that all respondents who are present at the time of the interview answer for themselves, SIPP accepts proxy interviews from another household respondent when necessary. Within each household, the instrument identifies a reference person, typically the first person listed as the owner or renter of the housing unit.

For Waves 2+ cases, SIPP switches from a household survey to a person-based survey. All people who were interviewed in the first wave of the panel and any children subsequently born to or adopted by them are designated as original sample members.  When visiting the original household, the interviewer determines whether one or more original sample members are present. If so, the interviewer updates the household roster, listing all people living or staying there, including anyone who may have joined the household, such as a new spouse or baby, and the dates they entered the household. 

For those remaining at the same address, the interviewer verifies that certain previously collected information still applies, completes the questionnaire for each person aged 15 years and older, and collects certain information for children under age 15. Information is likewise collected for all new household members. They are interviewed each wave so long as they live with an original sample member. Also noted are people who left the household and their dates of departure, along with their new address (if known). Figure 2-1 illustrates a few examples of SIPP’s following rules.

Following Movers

SIPP is a true longitudinal survey that tracks people over time. With few exceptions, original sample members are interviewed annually over the duration of the panel. When original sample members move to new addresses, interviewers attempt to locate and interview them every year. Figure 2 1 illustrates a few examples of SIPP’s following rules.

Movers are interviewed at their new addresses, along with other household members who are living or staying there. When original sample members move into households with other individuals not previously in the survey, the new individuals become part of the SIPP sample for as long as they continue to live with an original sample member. Similarly, when new individuals move in with original sample people after the first interview, they too become part of the SIPP sample for as long as they continue to live with an original sample member. If no original sample members live at an address where a previous interview was conducted, SIPP does not collect information from the new occupants of that address.

If an entire household moves, the interviewer tries to find the original sample people and interview them at their new address(es). Should the entire household move more than 100 miles away from a SIPP PSU, Field Representatives (FRs) attempt to conduct the interview by telephone. If the household cannot be reached, the sample members are dropped from the survey.

SIPP does not interview original sample members if they move outside the United States, become members of the military living in barracks, or become institutionalized (e.g., nursing home residents, prison inmates). The Census Bureau attempts to track such individuals so they can be interviewed should they return to the noninstitutionalized resident U.S. population.

Please see the SIPP Users’ Guide specific to your year or panel of analysis for more information on survey organization and interview procedures.