Through the 2008 Panel, SIPP was administered in panels and conducted in waves and rotation groups. Within a SIPP panel, the entire sample was interviewed at 4-month intervals. These groups of interviews are called waves. The first time an interviewer contacts a household is Wave 1; the second time is Wave 2, and so forth. As discussed in Chapter 3 of the SIPP Users' Guide, each wave contains core questions that are asked each time, along with topical questions that vary from one wave to the next.
Sample members within each panel are divided into four subsamples of roughly equal size; each subsample is referred to as a rotation group. One rotation group is interviewed each month. During the interview, information is collected about the previous 4 months, which are referred to as reference months. Thus, each sample member is interviewed every 4 months, with information about the previous 4-month period collected in each interview.
The original design of SIPP called for an initial selection of a nationally representative sample of households, with all adults in those households being interviewed once every 4 months over a 32-month period. In addition, interviews were to be conducted with any other adults living with original sample members at subsequent waves. The first sample, 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. The original goal was to have panels covering eight waves (32 months). In several instances, panels were terminated after seven waves (28 months). Two panels were terminated even earlier: 1988 (six waves) and 1989 (three waves).
With certain exceptions (Table 2-1), each panel overlapped part of the previous panel, with the result that there were two or three active panels at any given time. The overlap allows analysts to combine 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 with the 1996 Panel. Standard errors have remained small since the redesign because the 1996 and following panels each have target sample sizes of at least 37,000 interviewed households for Wave 1, almost twice the size of two of the previous panels.
|1984||Oct. 83||Jul. 86||20,897||9||2, 8|
|1985||Feb. 85||Aug. 87||14,306||8||2|
|1986||Feb. 86||Apr. 88||12,425||7||3|
|1987||Feb. 87||May 89||12,527||7||–|
|1988||Feb. 88||Jan. 90||12,725||6|
|1989||Feb. 89||Jan. 90||12,867||3|
|1990||Feb. 90||Sep. 92||19,800||8|
|1991||Feb. 91||Sep. 93||15,626||8|
|1992||Feb. 92||May 95||21,577||10||–|
|1993||Feb. 93||Jan. 96||21,823||9|
|1996||Apr. 96||Mar. 00||40,188||12|
|2001||Feb. 01||Jan. 04||50,500||9|
|2004||Feb. 04||Jan. 08||51,379||12|
|2008||Sept. 08||Dec. 13||52,031||16|
a No new panels in 1994 and 1995.
b Short waves contained three rotations instead of the standard four. Source: SIPP Quality Profile, 3rd Ed. (U.S. Census Bureau, 1998a).
At Wave 1, the interviewer visits the sampled address, compiles a household roster, and attempts to interview all members of the household who are 15 years of age or older. The interviewer decides whether each person is a household member by using rules that determine whether the person is a usual resident of the unit. Typically, a usual resident is one who sleeps there a majority of the time. While the Census Bureau prefers that all respondents who are present at the time of the interview answer for themselves, proxy interviews are accepted from another household respondent when necessary. Within each household a reference person is identified, typically it is the owner or renter of the housing unit. After Wave 1, the interviewer compiles (or updates) a separate household roster for each housing unit, listing all people living or staying at the unit, including anyone who may have joined the household, such as a new spouse or baby, and the dates they entered the household.
Also noted are people who left the household and their dates of departure. If some, but not all, sample members have moved since the last interview, the interviewer completes interviews at the original address and obtains the new address(es) of the individuals who moved. For those remaining at the same address, the interviewer verifies that certain previously collected information still applies, completes the questionnaire for each person 15 years of age or older, and collects certain information for children under age 15. Information is also collected for all new household members. Movers are interviewed at their new addresses, along with other household members they are living or staying with at the time. 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 members 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.
Interviewers rely on several sources of information to locate movers. At the first interview, the interviewer obtains the name, address, and telephone number of a person who could furnish the new address should the entire household move. If necessary, interviewers may contact neighbors, employers, mail carriers, real estate companies, rental agents, or postal supervisors to locate original sample members who have moved.
If an entire household moves, the interviewer tries to find the original sample members and interview them at their new address(es) if they remain in the locality. If the household relocates into or close to a different PSU, a SIPP interviewer in that area may interview them. For example, if a couple moves from Boston to Seattle, a SIPP interviewer in the Seattle area will likely interview the couple for the remaining waves of their panel. Should the entire household move more than 100 miles away from a SIPP PSU, attempts will be made to interview by telephone. If the household cannot be reached, the sample members will be dropped from the survey. Specifically, they will be treated as Type D noninterviews (Type D noninterviews are discussed in Chapter 2 of the SIPP Users' Guide).
If only some original sample members move, the interviewer completes interviews with all eligible household members at both the original address and the address(es) of those who have moved. If an original sample member leaves a SIPP household and the remaining original sample members cannot provide a new address, the interviewer will try to find the person through the means discussed above. Similar to what happens with a household, if an individual original sample member moves within the United States but more than 100 miles away from a SIPP PSU, a telephone interview will be attempted. When that is not possible, the person is treated as a Type D noninterview.
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, however. Should they return to the noninstitutionalized resident U.S. population, the Census Bureau will resume trying to interview them.
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