Results for the mid-September and late September 2004 surveys are based on telephone interviews conducted under the direction of Princeton Survey Research Associates International among two separate nationwide samples. The first survey, conducted September 17-21, interviewed 1,200 adults 18 years of age or older, and included 989 registered voters. The second survey, conducted September 22-26, interviewed 1,200 adults, and included 948 registered voters.
For results based on registered voters in either survey the sampling error is plus or minus 3.5 percentage points. For results based on the total sample in either survey, the margin of error is also plus or minus 3.5 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.