The analysis in this report is based on telephone interviews conducted May 3-7, 2017, among a national sample of 1,012 adults, 18 years of age or older, living in the continental United States (602 were interviewed via cellphone and 410 were interviewed on a landline telephone). The margin of error for the full sample is plus or minus 3.7 percentage points.
The survey was conducted under the direction of Social Science Research Solutions (SSRS). A combination of landline and cellphone random-digit-dial samples were used; both samples were provided by Marketing Systems Group. Interviews were conducted in English and Spanish.
The combined landline and cellphone sample is weighted using an iterative technique that matches gender, age, education, race, Hispanic origin and nativity, marital status and region to parameters from the U.S. Census Bureau’s 2016 Current Population Survey and population density to parameters from the 2010 decennial census. The sample also is weighted to match current patterns of telephone status (landline only, cellphone only, or both landline and cellphone), based on extrapolations from the 2016 National Health Interview Survey. The weighting procedure also accounts for the fact that respondents with both landline and cellphones have a greater probability of being included in the combined sample and adjusts for household size among respondents with a landline phone. The margins of error reported and statistical tests of significance are adjusted to account for the survey’s design effect, a measure of how much efficiency is lost from the weighting procedures.
The following table shows the unweighted sample sizes and the error attributable to sampling that would be expected at the 95% level of confidence for different groups in the survey:
Sample sizes and sampling errors for other subgroups are available upon request.
In addition to sampling error, one should bear in mind that question wording and practical difficulties in conducting surveys can introduce error or bias into the findings of opinion polls.
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