Appendix 1: Survey Methodology

This report includes survey data from several sources, including newly released results from a survey conducted June 28-July 9, 2012, by the Pew Research Center for the People & the Press and the Pew Research Center’s Forum on Religion & Public Life, among a national sample of 2,973 adults. The new survey is based on telephone interviews among adults 18 years of age or older living in all 50 U.S. states and the District of Columbia (1,771 respondents were interviewed on a landline telephone, and 1,202 were interviewed on a cell phone, including 596 who had no landline telephone). The survey was conducted by interviewers at Princeton Data Source and Universal Survey Center 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 http://people-press.org/methodology/.

The combined landline and cell phone sample are weighted using an iterative technique that matches gender, age, education, race, Hispanic origin and nativity and region to parameters from the March 2011 Census Bureau's Current Population 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 landline and cell phones (for those with both), based on extrapolations from the 2011 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 among respondents with a landline phone.

In partnership with Religion & Ethics NewsWeekly, the Pew Forum conducted an additional 511 interviews with religiously unaffiliated adults to produce a total sample of 958 unaffiliated respondents. These 511 additional interviews were conducted June 28-July 10, 2012, with religiously unaffiliated adults recruited by screening respondents from a fresh sample of landline and cell phone RDD phone numbers (261 interviews) and by recontacting respondents from recent surveys who had identified themselves as religiously unaffiliated (250 interviews). These additional interviews are used only when reporting on the religiously unaffiliated (including the unaffiliated subgroups – atheist, agnostic and those who describe their religion as “nothing in particular”); these interviews are not used when reporting results for the general public. For the RDD and cell phone recontact samples, respondents were initially selected in the same way as described above. For the landline recontact sample, interviewers asked to speak with the person who, based on gender and age, participated in the earlier survey. Once the selected respondents were on the phone, interviewers asked them a few questions and then asked their religious affiliation; those who are religiously unaffiliated continued with the remainder of the interview.

The weighting procedure for the additional interviews with religiously unaffiliated respondents used an iterative technique that included all of the parameters described above. In addition, the weighting accounted for the oversampling of unaffiliated respondents in the screened and callback samples, the type of unaffiliated respondent (atheist, agnostic or “nothing in particular”), as well as gender, age, region and the 2012 presidential vote preference among the unaffiliated. The parameters for the type of unaffiliated respondent and for gender, age and region among the unaffiliated are based on combined data from Pew Research Center surveys conducted from July 2011-June 2012. The parameter for the 2012 vote preference is based on the vote preferences of unaffiliated respondents in the main June 28-July 9 sample.

In total, the new survey includes 958 religiously unaffiliated respondents (447 from the main sample plus the 511 additional interviews). The following table shows the sample sizes and the error attributable to sampling that would be expected at the 95% level of confidence for key groups in this survey. Sampling errors and statistical tests of significance take into account the effect of weighting.

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.

The following questions on the survey were developed in consultation with Religion & Ethics NewsWeekly: Q21a-b, Q22, Q51-54 Q70, Q72, Q73a-g and Q97a-b.

This report also includes analysis of past survey data, including aggregated data from Pew Research Center surveys conducted over months or years, data from individual past Pew Research Center surveys and data from surveys conducted by other organizations. Full details on previous Pew Research Center surveys are available at www.pewresearch.org.