The analysis in this report is based on a compilation of 30 general population political surveys conducted by the Pew Research Center from January 2013 to December 2015. These interviews were conducted among adults 18 years of age or older, living in all 50 U.S. states and the District of Columbia. The analysis is based on the 32,247 cellphone respondents who provided valid ZIP codes, including 17,800 respondents who do not have a landline in their home.
The majority of these surveys were conducted by Princeton Survey Research Associates International; the March 2013, October 2013, 2014 Political Polarization and Typology and August 2014 surveys, as well as the 2015 Survey on Government, were conducted by Abt SRBI. A combination of landline and cellphone 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 http://www.pewresearch.org/methodology/u-s-survey-research/. Pew Research Center undertakes all polling activity, including calls to mobile telephone numbers, in compliance with the Telephone Consumer Protection Act and other applicable laws.
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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© Pew Research Center, 2016