SIPP sample members will be followed for 3 to 4 years, but, following SIPP practice since 1996, the panels will not overlap.
The first part of this chapter discusses concerns about moving SIPP to a nonoverlapping annual survey that relies on EHCs to develop month-to-month information on households. The remainder of the chapter discusses several additional issues related to SIPP design features (length and frequency of interviews, length and overlap of panels), content, timeliness, and budget that the panel thinks are important.
One feature of SIPP that the panel does not discuss is the sample size and design. The current design (see Chapter 2), which oversamples low-income populations based on the previous census, has been in use beginning with the 1996 panel, and sample sizes have been what the SIPP budget could afford. While data users would always prefer additional sample, SIPP users have found the sample sizes of recent SIPP panels (see Table 2-1) to be adequate for most purposes. The design, although not state representative, includes cases in every state (most of which are identified on the public-use microdata files) so that researchers can take account of differences in state tax and transfer program rules in their analyses. Ordinarily, the design would next be revised based on the 2010 census; however, that census will not include a long-form sample with data on income and other socioeconomic characteristics. Instead, the continuous American Community Survey (ACS) now provides that information (beginning in 2005). It will be necessary to redesign the SIPP sample to use the ACS, but it is our understanding that the ACS will not be available until 2012 for this purpose. As the ACS is relatively new and the shape of the reengineered SIPP is not finalized, the panel thinks it would be premature to comment on sample design issues.
As emphasized throughout this report, a unique feature of SIPP is its capacity to measure short-run dynamics. Monthly data on incomes, employment, program participation, health insurance coverage, and demographic characteristics of the household allow analysts to study transitions into marriage and divorce, transitions into and out of poverty, and transitions in health insurance coverage, at a monthly frequency. Monthly data also make SIPP particularly well suited for assessing eligibility for major transfer programs, since program rules typically depend on economic and demographic characteristics in the month or months prior to application. Studies of program take-up require careful calculations of eligibility—the denominator of the take-up rate—and high-quality measures of program participation—the numerator of the take-up rate. Studies of short-run dynamics are impossible with other nationally representative data sets,