Results for this survey are based on telephone interviews conducted under the direction of Princeton Survey Research Associates International among a nationwide sample of 1,505 adults, 18 years of age or older, from May 21-25, 2008. The following table shows the error attributable to sampling that would be expected at the 95% level of confidence for different groups in the survey:

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.