This report is based on data from numerous Pew Research Center surveys. Methodology summaries from the four main data sources are provided below.

Methodology of the 2015 Survey on Government

The analysis in this report is in part based on telephone interviews conducted Aug. 27-Oct. 4, 2015, among a national sample of 6,004 adults, 18 years of age or older, living in all 50 U.S. states and the District of Columbia (2,113 respondents were interviewed on a landline, and 3,891 were interviewed on a cellphone, including 2,227 who had no landline telephone). The survey was conducted under the direction of Abt SRBI. A combination of landline and cellphone random digit dial samples was 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 cellphone 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://www.pewresearch.org/methodology/u-s-survey-research/.

Data collection was divided equally into two phases (A and B) with independent samples, non-overlapping interview dates and separate weighting. The questionnaire for each phase contained a core set of measures of political attitudes and values, political engagement and demographic characteristics.

The combined landline and cellphone sample data are weighted using an iterative technique that matches gender, age, education, race, Hispanic origin and nativity and region to parameters from the Census Bureau’s 2013 American Community Survey and population density to parameters from the 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 2014 National Health Interview Survey. The weighting procedure also accounts for the fact that respondents with both landlines and cellphones have a greater probability of being included in the combined sample and adjusts for household size among respondents with landline phones. 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:

Methodology of the 2014 Political Polarization and Typology Survey

The analysis in this report is also based on telephone interviews conducted Jan. 23-March 16, 2014, among a national sample of 10,013 adults, 18 years of age or older, living in all 50 U.S. states and the District of Columbia (5,010 respondents were interviewed on a landline telephone, and 5,003 were interviewed on a cellphone, including 2,649 who had no landline telephone). The surveys were conducted under the direction of Abt SRBI. A combination of landline and cellphone RDD 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 cellphone 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 cellphone sample are weighted using an iterative technique that matches gender, age, education, race, Hispanic origin and nativity and region to parameters from the Census Bureau’s 2012 American Community Survey and population density to parameters from the decennial census. The sample also is weighted to match current patterns of telephone status and relative usage of landlines and cellphones (for those with both), based on extrapolations from the January-June 2013 National Health Interview Survey. The weighting procedure also accounts for the fact that respondents with both landlines and cellphones have a greater probability of being included in the combined sample and adjusts for household size among respondents with landline phones. Sampling errors and statistical tests of significance take into account the effect of weighting.

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:

Methodology of the September 2015 political survey

The demographic analysis in this report is based in part on telephone interviews conducted Sept. 22-27, 2015, among a national sample of 1,502 adults, 18 years of age or older, living in all 50 U.S. states and the District of Columbia (525 respondents were interviewed on a landline telephone, and 977 were interviewed on a cellphone, including 560 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 cellphone RDD 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 cellphone 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 cellphone sample are weighted using an iterative technique that matches gender, age, education, race, Hispanic origin and nativity and region to parameters from the Census Bureau’s 2013 American Community Survey and population density to parameters from the 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 2014 National Health Interview Survey. The weighting procedure also accounts for the fact that respondents with both landlines and cellphones have a greater probability of being included in the combined sample and adjusts for household size among respondents with landline phones. 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:

Methodology of the September 2008 survey

The demographic analysis in this report is also based on telephone interviews conducted Sept. 9-14, 2008, among a national sample of 2,982 adults, 18 years of age or older, living in the continental U.S. (2,250 respondents were interviewed on a landline telephone, and 732 were interviewed on a cellphone, including 254 who had no landline telephone). The survey was conducted by Princeton Survey Research Associates International and Abt SRBI Inc. A combination of landline and cellphone RDD samples were used; both samples were provided by Survey Sampling International. Interviews were conducted in English. Respondents in the landline sample were selected by asking for the youngest adult male who is now at home, and if no male was available interviewers asked to speak with the youngest adult female. Interviews in the cellphone 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 cellphone sample are weighted using an interative technique that matches gender, age, education, race, Hispanic origin, region and population density to parameters from the Census Bureau’s March 2007 Current Population Survey. The sample is also weighted to match current patterns of telephone status, based on the July-December 2007 National Health Interview Survey. The weighting procedure also accounts for the fact that respondents with both landlines and cellphones have a greater probability of being included in the combined sample. 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.