Wave1 supporting statement Part B.wpd

B. Collection of Information Employing Statistical Methods

1. Universe and Respondent Selection

There are approximately 270 million individuals in the potential SIPP respondent universe (civilian noninstitutionalized population based on the 2000 decennial census). The SIPP uses a multistage-stratified sample of the U.S. civilian noninstitutionalized population. The first stage involves the definition and division of the United States into groups of counties called the Primary Sampling Units (PSUs), which are assembled into homogeneous groups called strata. The second stage involves selection of units within the PSU.

The 2008 SIPP sample is the second sample for the SIPP to be fielded from the 2000 redesign of the sample. There are 351 PSUs in the 2000 redesigned SIPP and in sample for the 2008 Panel. The selected PSUs cover both urban and rural areas of the United States. Many of the PSUs in the 2000 SIPP sample design were also in the 1990 SIPP sample design. Definition of the PSUs, address lists, and area segments are all based on the 2000 decennial census.

Within each PSU, living quarters (LQs) are systematically selected from lists of addresses prepared for the 2000 decennial census. Other sampling techniques are used to represent new construction, group quarters, and areas where incomplete addresses are common. We oversampled low income households from the lists of addresses prepared for the census and from the lists of incomplete addresses. Wave 1 of the 2008 Panel sample will consist of approximately 65,300 designated LQs, of which approximately 52,900 will be occupied at the time of interview and about 45,000 will be interviewed. Each household contains, on average, 2.1 eligible respondents; therefore, there will be approximately 94,500 Wave 1 survey respondents.

2. Procedures for Collecting Information

The raw sample data will be weighted to independent population controls by age, race, household type, sex, and Hispanic¹ origin categories. After the weighting takes place, estimates, such as the number of people below the poverty level, number of social security recipients, and so forth, can be derived directly from the resulting database. The estimation process will also include derivation of sampling errors which is required to test the statistical validity of the survey estimates.

The precision of an estimate is shown by the coefficient of variation (CV), which is the standard error expressed as a percentage of the estimate. With the proposed sample design, statistics, such as the percentage of people in poverty (12 percent), are expected to have a CV of about 2 percent. We view the proposed sample design as the minimum required to provide reliable estimates for a variety of characteristics at the national level.

In sample households, all people 15 years old and over will be interviewed using regular proxy-respondent rules. In accordance with the longitudinal rules of the survey, every effort will be made to interview in Waves 2 through 9 the same people interviewed in Wave 1. Sample individuals (all household members present at the first interview) who move within or reasonably close to the boundaries of the PSUs from which the 2008 SIPP sample was selected will be followed and interviewed. Individuals 15 years old or over who enter the household after Wave 1 will be interviewed. The interviewing cycle for each wave (interview period) of the 2008 SIPP Panel is as follows:

Wave 1: February 1 through May 31, 2008.

Wave 2: June 1 through September 30, 2008.

Wave 3: October 1, 2008 through January 31, 2009.

Wave 4: February 1 through May 31, 2009.

Wave 5: June 1 through September 30, 2009.

Wave 6: October 1, 2009, through January 31, 2010.

Wave 7: February 1 through May 31, 2010.

Wave 8: June 1 through September 30, 2010.

Wave 9: October 1, 2010, through January 31, 2011.

The sample of 65,300 is systematically divided into quarters across the four months (rotations) of each wave. We expect to obtain 11,250 interviews each month in Wave 1.

A reinterview questionnaire also is administered to approximately 3,100 households in Waves 1-9 (Attachment D). The reinterview checks for survey falsifications. Households in reinterview are not eligible again for reinterview until the next calendar year. All Type A noninterviews are ineligible for reinterview. Whenever possible, reinterviews will be performed by telephone.

3. Methods to Maximize Response

In all SIPP Panels, we make special efforts to minimize noninterviews. In each Wave, every household in the active sample receives an advance letter that explains the purpose of the survey and why their cooperation is important. In Wave 1, each household is given a portfolio that contains reports created from the SIPP data and brochures informing respondents about the Census Bureau and our commitment to confidentiality. Each refusal case is sent a special refusal letter, and the case is assigned for a refusal follow-up by the program supervisor, senior FR, or an experienced FR. During the 1996 and 2001 SIPP Panels, the Census Bureau experimented with giving monetary incentives to households in order to maximize response. Based on results from these experiments, we implemented the use of incentives in the 2004 Panel and plan to use them in the 2008 Panel. During Wave 1, the respondents will be sent the Advance Letter in a Priority mail envelope. Over the course of the 2008 Panel, 100 percent of the survey households are eligible for a debit card worth $40. An incentive is offered to an eligible case if there are signs that the case is clearly planning to leave the survey. At the time the incentive is offered, it is made clear that payment is conditioned on a complete response to the questionnaire.

To adjust for those noninterviews that cannot be converted, a noninterview adjustment will be performed in the estimation procedure. Within the instrument, techniques are used that reference data provided on the prior interview to lessen recall problems and keep interview time to a minimum.

4. Tests of Procedures

The 1995 Dress Rehearsal was an important procedural test in preparation for future SIPP/CAPI Panel surveys. The dress rehearsal examined both the revised questionnaire design and automated collection methodology. Also, we tested the reinterview questionnaire to ensure that it integrated well with the rest of the survey data collection system. The dress rehearsal represented the final stage of an extensive series of cognitive review and instrument tests in the CAPI environment. The use of a complete CAPI environment is based on numerous tests using automated technology at the Census Bureau.

5. Contacts for Statistical Aspects and Data Collection

The Census Bureau will collect and process these data. Within the Census Bureau, the following individuals should be consulted for further information on their areas of expertise:

Sample Design

Tracy Mattingly Chief, SIPP Branch

Demographic Statistical Methods Division

301-763-6445

Data Content

Robert Kominski Assistant Division Chief, Population Division

301-763-2120

David Johnson Chief, Housing and Household Economic Statistics Division

301-763-6443

Data Collection and Tabulation

Patrick Benton Chief, Income Surveys Branch

Demographic Surveys Division

301-763-4618

Attachments

A. SIPP-CAPI Wave 1 Core and Topical Module Items Booklet

B. SIPP-28105(L)–Director's Letter

C. SIPP-28003–Reminder Card

D. SIPP-CAPI Wave 1 Reinterview Questions

1Hispanics may be of any race.