Interviewing for the survey was conducted by telephone March 8-28, 2006 among a sample of 1,503 adults age 18 and older. Approximately half of the interviews (752) were conducted using a landline number frame, with the remainder conducted from a cell phone number frame (751). Both sampling frames were designed by Survey Sampling, Inc. In order to compensate respondents for any toll charges incurred, those interviewed from the cell phone frame were offered an incentive of $10 for completing the survey. Interviewing was conducted by the research firm Schulman, Ronca & Bucuvalas, Inc.
The data were weighted using demographic weighting parameters derived from the March 2005 Census Bureau’s Current Population Survey, along with estimates of current patterns of telephone status in the U.S., using an iterative technique that simultaneously balances the distributions of all weighting parameters.
For results based on the total sample, one can say with 95% confidence that the error attributable to sampling is plus or minus 3 percentage points. Sampling error for subgroups in the sample would be larger than 3 points. In addition to sampling error, one should bear in mind that question wording and practical difficulties in conducting surveys can introduce error or bias into the findings of opinion polls.