Results for this survey are based on telephone interviews conducted under the direction of Princeton Survey Research Associates International among a nationwide sample of 1,501 adults, 18 years of age or older, from September 12-16, 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. For results based on Form 1 (N=760) or Form 2 (N=741), one can say with 95% confidence that the error attributable to sampling is plus or minus 4 percentage points. For results based on Democratic and Democratic-leaning registered voters (N=568) or Republican and Republican-leaning registered voters (N=467) the margin of error is plus or minus 5 percentage 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.