For the cell phone sample, SSI begins with a monthly listing of every existing telephone area code and exchange. About half of these are pooled by their producers in contiguous groups of 10 100-block phone numbers, or 1,000-blocks, with information including whether each pooled 1,000-block does or does not include cell phone numbers, either solely or on a shared basis with landline numbers.
All cell-inclusive 1,000-blocks are included in the cell phone sample. For numbers that are not 1,000-block pooled, cell phone service information is available at the exchange level only; therefore all numbers in those exchanges also are included. All numbers used in cell phone sampling are then handled at the 100-block level. Given the absence of any cell phone directory, all 100-blocks in dedicated wireless exchanges and 1,000-blocks used for sampling purposes are considered active.
For exchanges or 1,000-blocks that have been classified by their carrier as providing both landline and wireless service, each 100-block is compared to the database of landline 100-blocks; 100-blocks that appear on the landline frame are removed from the wireless frame and 100-blocks with no directory-listed numbers are retained. This ensures that the wireless frame and list-assisted RDD frame are mutually exclusive while still providing coverage of prefixes and 1,000-blocks that are classified as including both landline and wireless service.
Each 100-block is assigned to a county based on the billing coordinates of the exchange. The database is sorted by county code, carrier name and 100-block. A sampling interval is determined by dividing the universe of eligible 100-blocks by the desired sample size. From a random start within the first sampling interval, a systematic nth selection of 100-blocks is performed and a 2-digit random number between 00 and 99 is appended to each selected 100-block stem.
In each sample, phone numbers are released for interviewing in replicates by Census region (cell) or division (landline) to allow for sample control. Numbers are called multiple times during the field period in multi-night polls; the standard for full-length ABC/Post polls is a minimum of six calls to each number. Interviews are conducted via a computer-assisted telephone interviewing (CATI) system. Abt SRBI’s professional interviewers, and their supervisors, are extensively trained in interviewing practices, including techniques designed to achieve the highest possible respondent cooperation.
For landline respondents, interviewers ask to speak with the youngest male or youngest female at home. Cell-only respondents are screened for age eligibility (18+). Cell-only respondents are not offered compensation, but a reimbursement check is offered if use of minutes is raised as an objection. Cell sample respondents’ place of residence is checked and their Census region adjusted accordingly if necessary.
As of April 2013, Spanish-language interviewing was added to full-length ABC/Post polls for respondents who indicate a preference to be interviewed in Spanish. Spanish-language interviewing in SSRS omnibus surveys began in October 2009.
Data are adjusted to account for the greater probability of respondents who have both a cell and landline phone, compared with those who are cell-only or landline-only. The data then are weighted using demographic information from the U.S. Census and NHIS to adjust for variance from population values.