Most of the analysis in this report is based on telephone interviews conducted July 20-24, 2011 among a national sample of 1,501 adults 18 years of age or older living in the continental United States (916 respondents were interviewed on a landline telephone, and 585 were interviewed on a cell phone, including 254 who had no landline telephone). The survey was conducted by interviewers at Princeton Data Source under the direction of Princeton Survey Research Associates International. A combination of landline and cell phone random digit dial samples were used; both samples were provided by Survey Sampling International. Interviews were conducted in English and Spanish. Respondents in the landline sample were selected by randomly asking for the youngest adult male or female who is now at home. Interviews in the cell sample were conducted with the person who answered the phone, if that person was an adult 18 years of age or older. For detailed information about our survey methodology, see https://alpha.pewresearch.org/pewresearch-org/politics/methodology/
The combined landline and cell phone sample are weighted using an iterative technique that matches gender, age, education, race, Hispanic origin, region, and population density to parameters from the March 2010 Census Bureau’s Current Population Survey. The sample also is weighted to match current patterns of telephone status and relative usage of landline and cell phones (for those with both), based on extrapolations from the 2010 National Health Interview Survey. The weighting procedure also accounts for the fact that respondents with both landline and cell phones have a greater probability of being included in the combined sample and adjusts for household size within the landline sample. Sampling errors and statistical tests of significance take into account the effect of weighting. The following table shows the 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.
Some of the analysis in this report is based on telephone interviews conducted June 23-26, 2011, July 21-24, 2011, and August 4-7, 2011.
The June 23-26, 2011, survey was conducted among a national sample of 1,005 adults 18 years of age or older living in the continental United States (672 respondents were interviewed on a landline telephone, and 333 were interviewed on a cell phone, including 142 who had no landline phone.
The July 21-24, 2011, survey was conducted among a national sample of 999 adults 18 years of age or older living in the continental United States (602 respondents were interviewed on a landline telephone, and 397 were interviewed on a cell phone, including 169 who had no landline telephone).
The August 4-7, 2011, survey was conducted among a national sample of 1,001 adults 18 years of age or older living in the continental United States (601 respondents were interviewed on a landline telephone, and 400 were interviewed on a cell phone, including 164 who had no landline telephone.)
The surveys were conducted by interviewers at Princeton Data Source under the direction of Princeton Survey Research Associates International. For each survey, a combination of landline and cell phone random digit dial samples were used; both samples were provided by Survey Sampling International. Interviews were conducted in English. Respondents in the landline sample were selected by randomly asking for the youngest adult male or female who is now at home. Interviews in the cell sample were conducted with the person who answered the phone, if that person was an adult 18 years of age or older.
The combined landline and cell phone sample are weighted using an iterative technique that matches gender, age, education, race, Hispanic origin, region, and population density to parameters from the March 2010 Census Bureau’s Current Population Survey. The sample also is weighted to match current patterns of telephone status, based on extrapolations from the 2010 National Health Interview Survey. The weighting procedure also accounts for the fact that respondents with both landline and cell phones have a greater probability of being included in the combined sample and adjusts for household size within the landline sample. Sampling errors and statistical tests of significance take into account the effect of weighting. The following table shows the 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.