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Appendix IV - Survey Methodology
Telephone Survey
The Haas Center staff utilized Oppenheim Research, a telephone survey firm located in Tallahassee, Florida, to conduct the statewide telephone survey. Oppenheim Research obtained the home telephone numbers used in the survey from Survey Sampling International (SSI). Generating a truly random sample of telephone numbers for individuals in a particular geographic region is becoming more and more challenging. According to SSI, “In 2007, roughly 16% of all households had only wireless or cell phone service and only 82% of households could be reached on a landline telephone. Approximately 30% of the landline telephone households in the U.S. have unlisted numbers. Each year, about 20% of American households move, so that 12-15% of the residential numbers in a typical directory are disconnected over the life cycle of the directory. Samples drawn entirely from directories, and “plus-one” techniques based on directory seed numbers, often significantly under-represent unlisted households.”3
In order to overcome these difficulties, SSI developed random digit (RDD) methods. This method yields more active numbers and faster survey completion. In addition to the RDD method, phone numbers were distributed across all counties included in the sample (in this case, the State of Florida) in proportion to their density of listed telephone numbers. “All blocks within a county are organized in ascending order by area code, exchange, and block number. Once the quota has been allocated to all counties in the frame, a sampling interval is calculated by summing the number of listed residential numbers in eligible blocks within the county and dividing that sum by the number of sampling points assigned to the county. From a random start between zero and the sampling interval, blocks are systematically selected in proportion to their density of listed households. Once a block has been selected, a two-digit number is systematically selected in the range 00-99 and is appended to the exchange and block to form a 10-digit telephone number.”4 This methodology provides a very efficient random digit sample. Each county will have a probability of selection equal to its share of listed telephone households in the county. Business numbers were not included. Additionally, mobile phone numbers were not included.
Initially, Oppenheim Research ordered 15,000 telephone numbers. Of those 15,000 they used 9,595 to obtain the 905 survey completions and a response rate of 9.4%. Several screening criteria were utilized at the beginning of the survey. After introducing the survey, respondents were asked if they were over 18 years of age or if there was someone in the household who was over 18. If they or someone in the household was over 18, they were then asked if they had visited a public library in person or online in the last 12 months. If the answer to that was no, they did not continue with the survey. The survey was conducted over a 6-week period beginning November 11, 2009 and ending December 18, 2009.
3 SSI, RDD Landline Sample Methodology, http://www.surveysampling.com/sites/all/files/imce/RDDLandline.pdf
4 Ibid
