Survey Methods
Results are based on an aggregated sample of telephone interviews with 4,014 national adults, aged 18 and older, conducted in November 2004, November 2005, November 2006, and November 2007. For results based on the total aggregated sample of national adults, one can say with 95% confidence that the maximum margin of sampling error is ±2 percentage points. The margin of error for smaller subsamples reported in this analysis will be larger.
In addition to sampling error, question wording and practical difficulties in conducting surveys can introduce error or bias into the findings of public opinion polls.