Results for this report are based on telephone interviews conducted under the direction of Princeton Survey Research Associates International among a sample of 820 adults, 18 years of age or older, from October 3-5, 2008. The interviews were conducted among a population of 1,505 adults previously interviewed by Pew from September 27-29. Interviews were conducted on
both landline telephones (N=617) and cell phones (N=203). The data were weighted using demographic weighting parameters derived from the March 2007 Census Bureau’s Current Population Survey, along with an estimate of current patterns of telephone status in the U.S. derived from the 2007 National Health Interview Survey.
In order to assure comparability of the recontacted cases with the original sample, the data were also weighted to match the distribution of the Sept. 27-29 sample results on key political questions, including leaned party affiliation, whether Sarah Palin is qualified to be president and whether the government plan to secure the markets is a good or bad thing to do. This step helps to minimize bias that could occur because certain types of respondents may have been easier or harder to re-interview. The weighting used an iterative technique that simultaneously balances the distributions of all weighting parameters.
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:
|Group||Sample Size||Plus or minus…|
|Total sample||820||4.5 percentage points|
|Registered voters||710||4.5 percentage points|
|Republican voters||203||8.0 percentage points|
|Democratic voters||271||7.0 percentage points|
|Independent voters||207||8.0 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.