Unlike sampled landlines, sampled wireless phone numbers are not pre-dialed via non-ringing auto-dialer, and are hand-dialed by Abt SRBI interviewers.
Sample Management and Interviewing
As noted, ABC’s approach is to view these landline and wireless sampling frames as mutually exclusive; the purpose of the wireless frame is to address the landline frame’s non-coverage of cell-only households, using the most recent estimates from the federal government’s in-person National Health Interview Survey.
Abt SRBI draws wireless sample proportionate to its distribution in the country’s four U.S. Census regions, per NHIS data. Respondents are screened for cell-only status; those with landlines they use to take calls are not interviewed by cell phone, since they are covered in the separate landline frame. Cell-only respondents’ place of residence is checked and their Census region adjusted accordingly, if necessary.
Landline sample is drawn proportionate to its estimated distribution in the country’s nine Census divisions.
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. 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.
Cell-only respondents are not offered compensation. A reimbursement check is offered if use of minutes is raised as an objection and the respondent subsequently supplies his or her mailing address; on average this occurs in six cases per survey, out of a current per-survey sample of approximately 200 cell-only respondents.
Final data are weighted using demographic information from the U.S. Census to adjust for sampling and non-sampling deviations from population values. Until 2008 ABC News used a cell-based weighting system in which respondents were classified into one of 48 or 32 cells (depending on sample size) based on their age, race, sex and education; weights were assigned so the proportion in each cell matched the Census Bureau’s most recent Current Population Survey. To achieve greater consistency and reduce the chance of large weights, ABC News in 2007 tested and evaluated iterative weighting, commonly known as raking or rim weighting, in which the sample is weighted sequentially to Census targets one variable at a time, continuing until the optimum distribution across variables (again, age, race, sex and education) is achieved. ABC News adopted rim weighting in January 2008. Weights are capped at lows of 0.2 and highs of 6.
In procedures since the start of the dual-frame design, cell-only and landline samples first are weighted by Census region to their respective proportions of the population (per NHIS cell-only estimates). The combined sample is then rim-weighted to full-population Census parameters for age, race, sex and education. A post-weight is applied to the cell-only sample if needed to correct its final proportion within the full sample.