Appendix 1: About the Research
About the Research
The contents of this book are based on extensive, ongoing, nationwide research conducted by Barna Group. We used data from twenty surveys, encompassing interviews with more than 20,000 churched and unchurched adults. The number of unchurched adults involved was 6,276.
These surveys were done using random digit-dial telephone samples for landlines and listed cell phone samples for calls to mobile phones. Each of the studies entailed completing interviews with a minimum of 1,000 randomly chosen adults. The samples were developed to provide a reliable representation of the national population of people ages eighteen or older living within the forty-eight continental states. The estimated maximum sampling error for each survey of 1,000 adults was plus or minus 3.1 percentage points at the 95 percent confidence level; the maximum sampling error estimate diminished as sample size increased. The number of interviews completed with cell-phone owners was based on federal government estimates of the number of cell-only households.
The January 2011, 2012, 2013, and 2014 surveys also included samples of approximately 1,000 adults conducted online. Those studies relied on a research panel called KnowledgePanel®, part of GFK Custom Research North America. It is a probability-based online non-volunteer access panel. Panel members are recruited using a statistically valid sampling method with a published sample frame of residential addresses that covers approximately 97 percent of US households. Sampled non-Internet households, when recruited, are provided a netbook computer and free Internet service so they may also participate as online panel members. KnowledgePanel consists of about 50,000 adult members (ages eighteen and older) and includes persons living in cell-only households.
In all of these surveys, regional and ethnic quotas were designed to ensure that the final group of adults interviewed reflected the distribution of adults nationwide and adequately represented the three primary ethnic groups within the United States (those groups that comprise at least 10 percent of the population: white, black, and Hispanic). Those quotas were based on current US Census Bureau data regarding the population. Additional quotas were employed to balance the gender of respondents included in the samples. Upon completion of a survey, the data were run and the demographic outcomes were compared to the census statistics on key demographic attributes. In some cases the full survey database was then statistically weighted to bring the database into closer approximation of the true population proportions.
Surveys Included in the Unchurched Database
Study conducted in:
Total sample
Unchurched adult sample
January 2008
1,004
277
May 2008
1,003
331
July 2008
1,005
301
August 2008
1,005
305
October 2008
1,014
327
November 2008
1,198
299
July 2009
1,003
315
September 2009
1,004
284
January 2010
1,008
240
February 2010
1,005
305
August 2010
1,002
368
December 2010
1,022
311
January 2011
1,622
615
August 2011
1,007
324
January 2012
2,025
920
March 2012
1,020
386
April 2012
1,062
340
May 2012
1,009
371
November 2012
1,008
338
January 2013
2,083
952
January 2014
1,024
556