Results for this report are based on telephone interviews conducted from November 6-9, 2008 under the direction of Princeton Survey Research Associates International among a sample of 1,500 voters ("Voters" are those respondents who said they voted in the 2008 election.). The interviews were conducted among a population of 2,599 registered voters, 18 years of age or older, previously interviewed by Pew from October 16-19, 2008. Interviews were conducted on both landline telephones and cell phones (1,125 respondents were interviewed on a landline telephone, and 375 were interviewed on a cell phone, including 114 who had no landline telephone).

The combined landline and cell phone samples are weighted using an iterative technique that matches gender, age, education, race/ethnicity, region, and population density to parameters from the March 2007 Census Bureau's Current Population Survey. The sample is also weighted to match current patterns of telephone status and relative usage of landline and cell phones (for those with both), based on extrapolations from the 2007 National Health Interview Survey. The weighting procedure also accounts for the fact that respondents with both landline and cell phones have a greater probability of being included in the sample.

To improve comparability of the recontacted cases with the final 2008 election results, the data were also weighted to reflect the margin of the election results (an approximately 7-point Obama advantage). This step helps to minimize bias that could occur because certain types of respondents may have been easier or more difficult to re-interview.

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.

 
ABOUT THE CENTER

The Pew Research Center for the People & the Press is an independent opinion research group that studies attitudes toward the press, politics and public policy issues. We are sponsored by The Pew Charitable Trusts and are one of seven projects that make up the Pew Research Center, a nonpartisan "fact tank" that provides information on the issues, attitudes and trends shaping America and the world.

The Center's purpose is to serve as a forum for ideas on the media and public policy through public opinion research. In this role it serves as an important information resource for political leaders, journalists, scholars, and public interest organizations. All of our current survey results are made available free of charge.

All of the Center’s research and reports are collaborative products based on the input and analysis of the entire Center staff consisting of:

 Andrew Kohut, Director
 Scott Keeter, Director of Survey Research
 Carroll Doherty and Michael Dimock, Associate Directors
 Kim Parker, Senior Researcher
 Michael Remez, Senior Writer
Juliana Menasce Horowitz, Robert Suls, Shawn Neidorf, Leah Christian and Jocelyn Kiley,
Research Associates
 Kathleen Holzwart and Alec Tyson, Research Analysts