Survey Methodology

The Research Behind Cities

The data reported in this summary are based upon telephone and online interviews with nationwide random samples of 42,855 adults conducted over a seven year period, ending in May 2012.

The maximum margin of sampling error associated with the aggregate sample is ±0.5 percentage points at the 95% confidence level. All non-institutionalized adults in the 48 contiguous states were eligible to be interviewed and the distribution of respondents in the survey sample corresponds to the geographic dispersion of the U.S. adult population. Some interviews were conducted in Spanish, but the vast majority of the interviews were completed in English.

All telephone interviews were conducted by Barna Group. All households were selected for inclusion in the sample using a random-digit dial technique, which allows every telephone household in the nation to have an equal and known probability of selection.  Households selected for inclusion in the survey sample received multiple callbacks to increase the probability of obtaining a representative distribution of adults. Regional quotas were used to ensure that sufficient population dispersion was achieved. There were also minimum and maximum ranges placed on the distribution of respondents within several demographic variables that were tracked during the field process to ensure that statistical weighting would not be excessive. When a particular attribute reached one of the parameters, the sampling selection process was varied to preclude individuals who did not meet the necessary demographic criterion, with the interviewer seeking a person from the same household who fit the desired criterion.  Up to 30% of telephone interviewing was conducted on cell phones in the data represented in Cities.

Online interviews were conducted using an online research panel called KnowledgePanel® based on probability sampling that covers both the online and offline populations in the U.S. The panel members are randomly recruited by telephone and by self-administered mail and web surveys. Households are provided with access to the Internet and hardware if needed. Unlike other Internet research that covers only individuals with Internet access who volunteer for research, this process uses a dual sampling frame that includes both listed and unlisted phone numbers, telephone and non-telephone households, and cell-phone-only households. The panel is not limited to current Web users or computer owners. All potential panelists are randomly selected to join the KnowledgePanel; unselected volunteers are not able to join.

The survey questions pertaining to faith and demographics were analyzed in reference to two different geographic perspectives: by DMA and by state. The label “DMA” stands for Designated Market Area and represents a unique geographic area that also serves as a commonly accepted media market as defined by The Neilsen Company.  DMAs have been configured so that the entire U.S. is assigned to one – and only one – of 210 DMAs in the country and are based on the television viewing habits of the residents in each county.

While there are 210 DMAs, this report contains data for just 96 of them. Those are the areas in which we had a sufficient number of completed surveys with people from a given market. In most markets, we had a sample of 150 or more; a few smaller markets had a minimum of 100. We used the same minimum-level criteria for the states analyzed in this report.