Results for this survey are based on telephone interviews conducted under the direction of Princeton Survey Research Associates International among a nationwide sample of 1,502 adults, 18 years of age or older, from February 1-13, 2007. 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.
Results from a separate survey in which we tested “multiple choice” versions of key questions are based on 1,017 interviews conducted March 9-12, 2007 under the direction of Opinion Research Corporation. The error attributable to sampling is plus or minus 3.5 percentage points (95% confidence) for these questions.
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.