Appendix C: Methodology

Methodology and Design

Provided by Princeton Survey Research International.

The Personal Networks and Community Survey, sponsored by the Pew Internet & American Life Project, obtained telephone interviews with a nationally representative sample of 2,512 adults living in households in the continental United States. The survey was conducted by Princeton Survey Research International. The interviews were conducted in English by Princeton Data Source, LLC between July 9, 2008 and August 10, 2008.  Statistical results were weighted to correct known demographic discrepancies.  The margin of sampling error for the complete set of weighted data is ±2.1%. 

Sample Design

A combination of landline and cellular random digit dial (RDD) samples was used to represent all adults in the continental United States who have access to either a landline or cellular telephone. Both samples were provided by Survey Sampling International, LLC (SSI) according to PSRAI specifications.

Numbers for the landline sample were selected with probabilities in proportion to their share of listed telephone households from active blocks (area code + exchange + two-digit block number) that contained three or more residential directory listings. The cellular sample was not list-assisted, but was drawn through a systematic sampling from 1,000 blocks dedicated to cellular service according to the Telcordia database.

Questionnaire Development and Testing

A questionnaire was developed by PSRAI in collaboration with Keith N. Hampton and staff of the Pew Internet & American Life Project. To improve the quality of the data, the questionnaire was pretested with a small number of respondents using RDD telephone number samples. The pretest interviews were conducted using experienced interviewers who judged the quality of the answers and the degree to which respondents understood the questions.  Using recordings, PSRAI staff reviewed the pretest interviews. Some final changes were made to the questionnaire, based on the reviewed pretest interviews.

Contact Procedures

Interviews were conducted between July 9, 2008 and August 10, 2008. As many as ten attempts were made to contact every sampled telephone number. Samples were released for interviewing in replicates, which are representative subsamples of the larger sample. Using replicates to control the release of the sample ensured that complete call procedures were followed for the entire sample.

For the landline sample, interviewers asked to speak with the youngest adult male currently at home. If no male were available, interviewers asked to speak with the youngest female at home. This systematic respondent selection technique has been shown to produce samples that closely mirror the population in terms of age and gender. For the cellular sample, interviews were conducted with the person who answered the phone. Interviewers verified that the person was an adult and in a safe place before administering the survey. Cellular sample respondents were offered a post-paid, cash incentive for their participation.

Weighting and Analysis

Weighting is generally used in survey analysis to compensate for sample designs and patterns of nonresponse that might bias results. A two-stage, weighting procedure was used to weight this dual-frame sample. A first-stage weight of 0.5 was applied to all dual-users to account for the fact that they were included in both sample frames.¹⁵ landline respondents who have a working cell phone, or [b] cell phone respondents who have a regular landline phone where they currently live.] All other cases were given a first-stage weight of 1. The second stage of weighting balanced sample demographics to population parameters. The sample was balanced to match national population parameters for sex, age, education, race, Hispanic origin, region (U.S. Census definitions), population density, and telephone usage. The basic weighting parameters came from a special analysis of the Census Bureau’s 2007 Annual Social and Economic Supplement (ASEC) that included all households in the continental United States that had a telephone. The cell phone usage parameter came from an analysis of the July-December 2006 National Health Interview Survey.

Weighting was accomplished using Sample Balancing, a special iterative sample-weighting program that simultaneously balances the distributions of all variables using a statistical technique called the Deming Algorithm. Weights were trimmed 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 national population.

Response Rate

The response rate estimated the fraction of all eligible respondents in the sample who were ultimately interviewed. At PSRAI, response rate is calculated by taking the product of three component rates:¹⁶

• contact rate – the proportion of working numbers where a request for interview was made;¹⁷
• cooperation rate – the proportion of contacted numbers where a consent for interview was at least initially obtained, versus those refused;
• completion rate – the proportion of initially cooperating and eligible interviews that were completed.

The response rate for the landline sample was 21%. The response rate for the cellular sample was 22 %.