Results for the national survey are based on telephone interviews conducted under the direction of Schulman, Ronca, & Bucuvalas, Inc. among a nationwide sample of 1,399 adults, 18 years of age or older, from November 20-26, 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 likely Democratic primary voters (N=467), the error attributable to sampling is plus or minus 5 percentage points.
Results for the state surveys are based on telephone interviews with a sample of 5,462 adults living in Iowa, New Hampshire, and South Carolina, conducted by Princeton Data Source, LLC under the direction of Princeton Survey Research Associates International, from November 7-25, 2007.
The Iowa survey interviewed a total of 2,111 registered voters, including 460 who say they will definitely or probably attend a Democratic caucus. The margin of error for those likely to attend a Democratic caucus is +-5.5%.
The New Hampshire survey interviewed a total of 1,300 registered voters, including 594 who plan to vote in the Democratic primary. The margin of error for those who plan to vote in the Democratic primary is +-5%.
The South Carolina survey interviewed a total of 1,200 registered voters, including 373 who plan to vote in the Democratic primary. The margin of error for those who plan to vote in the Democratic primary is +-6%.
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.