Adding a topical supplement to an existing national survey might be a useful approach when a large amount of new information is required or when there is a need to study a specific subpopulation that cannot be easily identified with existing information. In either case, an existing, large national survey could act as the screener. The existing parent survey would also provide additional information that enhances the supplement, making an addition to an existing survey more efficient than conducting a stand-alone survey. The existing national survey to be used as the parent survey would need to include disability identifiers; otherwise, screening questions would need to be added. The inclusion of the six-question series on disability in additional federal surveys could expand the potential opportunities to use these questions as screeners for disability modules or supplements to existing national surveys.
Stapleton et al. (2009a) describe three general models for fielding topical supplements to existing surveys that are currently used in national surveys: topical modules, topical question batteries, and topical surveys. These models can be considered for purposes of conducting a national disability survey, which we discuss in Chapter IV.
Topical modules are supplementary questionnaires administered during a longitudinal survey that contains information on other topics, such as employment. The SIPP exemplifies this model because it is built around a core of labor force, program participation, and income questions designed to measure the economic circumstances of people in the United States. In addition, the survey was designed to provide a broader context for the analysis of income and program participation dynamics by adding questions on a variety of topics, such as living circumstances and personal assets, not covered in the core survey and that presumably do not change substantially during the short time intervals of the longitudinal data collection. Because the SIPP is designed to collect longitudinal information at relatively short intervals, it is unique in offering many opportunities to survey the same respondents and to spread the burden of collecting more detailed topical information. This is not the case with other large national surveys. Although repeated over time, most large national surveys are cross-sectional and thus offer only one opportunity to identify the subsample of interest and collect the additional topical information; this can substantially increase respondent burden if the topical supplement is large. The CPS, because it is fielded monthly, also offers multiple opportunities within a year to administer a topical supplement and has been used to do so quite frequently. The planned disability supplement to the CPS being developed by DOL is an example.
Topical question batteries are sets of questions that can be added to a core survey questionnaire but, unlike topical modules, are only asked of a subsample. An example of this model is the BRFSS, where topical supplements can be used in concert with the core national survey and administered in a single interview for a subgroup of people being interviewed. This approach differs from the SIPP topical module in that the topical question batteries are optional and selected for administration at the discretion of the states, which are responsible for administering the BRFSS. Under cooperative agreements with the Centers for Disease Control and Prevention (CDC), each state administers the core BRFSS questionnaire every year. In addition, each year the CDC offers a variety of approved topical modules that can be used by the states at their discretion and cost. States also are permitted to add their own sets of questions, subject to certain procedures and requirements, and at their own expense.
Topical surveys appear to be stand-alone surveys, but in fact derive their samples from a parent survey and therefore are essentially extensive topical modules of the parent survey. For example, the ATUS sample comes from the CPS, and the MEPS sample is derived from the NHIS. In each, supplemental interviews are conducted separately from the original interviews but the data from the original survey can be combined and used with the topical survey data. The NHIS-D also falls in this category, although unlike the other examples, the NHIS-D was designed as a one-time survey.