The 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 44,465 bilingual telephone interviews (including 17,968 cell phone interviews) conducted between March 3 and December 29, 2013 by professional interviewers under the direction of SSRS. The AVA was made possible by generous grants from The Ford Foundation and the Nathan Cummings Foundation.
Roughly 1,000 interviews were completed each week, with roughly 400 interviews conducted among respondents on their cell phones. In each week, interviewing occurred over a five-day period, from Wednesday through Sunday. 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 is 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. Telephone usage refers to whether respondents have only a landline telephone, only a cell phone or both types. 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 2013 National Health Interview Survey. All other weighting parameters were derived from an analysis of the U.S. Census Bureau's March 2013 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 margin of error for total sample is +/- 0.5 percentage points at the 95% level of confidence. The design effect for total sample is 1.3. In addition to sampling error, surveys may also be subject to error or bias due to question wording, context, and order effects.
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