2015 Methodology Download PDF

The 2015 American Values Atlas (AVA) is a project of Public Religion Research Institute (PRRI). Results for all demographic, religious affiliation, and political affiliation questions were based on 81,970 bilingual telephone interviews (including 40,968 cell phone interviews) conducted between January 7, 2015 and January 7, 2016 by professional interviewers under the direction of SSRS. Results for questions on specific issues (e.g. immigration and LGBTQ issues) are based on a subset of 42,586 telephone interviews conducted between April 29, 2015 and January 7, 2016. The AVA was made possible by generous grants from The Ford Foundation, The Carnegie Corporation of New York, the Arcus Foundation, the Gill Foundation and the Nathan Cummings Foundation.

Throughout 2015, at least 1,000 interviews were completed each week, with about 500 interviews conducted among respondents on their cell phones. Each week, interviewing occurred over a five-day period, from Wednesday through Sunday or from Thursday through Monday. The selection of respondents within households was accomplished by randomly requesting to speak with the youngest adult male or female currently living in the household.

Data collection was based on stratified, single-stage, random-digit-dialing (RDD) of landline telephone households and randomly generated cell phone numbers. The sample was designed to represent the total U.S. adult population from all 50 states, including Hawaii and Alaska. The landline and cell phone samples were provided by Marketing Systems Group.

The weighting was accomplished in two separate stages. The first stage of weighting corrects for different probabilities of selection associated with the number of adults in each household and each respondent's telephone usage patterns. In the second stage, sample demographics were balanced to match target population parameters for gender, age, education, race and Hispanic ethnicity, region (U.S. Census definitions), population density, and telephone usage. The population density parameter was derived from 2010 Census data. The telephone usage parameter came from an analysis of the July-December 2014 National Health Interview Survey. All other weighting parameters were derived from an analysis of the U.S. Census Bureau's March 2015 Current Population Survey.

The sample weighting was accomplished using iterative proportional fitting (IFP), a process that simultaneously balances the distributions of all variables. Weights are trimmed so that they do not exceed 4.0 or fall below 0.25 to prevent individual interviews from having too much influence on the final results. The use of these weights in statistical analysis ensures that the demographic characteristics of the sample closely approximate the demographic characteristics of the target populations.

The table below shows the sample sizes for all 50 states and 30 metro areas for both the total sample and issue subsample. The margin of error for total sample is +/- 0.4 percentage points at the 95% level of confidence. The design effect for total sample is 1.4. In addition to sampling error, surveys may also be subject to error or bias due to question wording, context, and order effects.

Sample Sizes for States and Metro Areas