Results for this survey are based on telephone interviews conducted under the direction of Princeton Survey Research Associates International among a nationwide sample of 1,503 adults, 18 years of age or older, from March 21-25, 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.
Q.21 is based on 1,245 interviews conducted March 22-25. The error attributable to sampling is plus or minus 3.5 percentage points (95% confidence) for this question.
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.