How the AP-Gfk Poll was conducted
The Associated PressThe Associated Press-GfK Poll on the 2008 presidential race was conducted by GfK Roper Public Affairs & Media from Sept. 5-10, 2008. It is based on landline and cell phone telephone interviews with a nationally representative random sample of 1,217 adults, which included 812 likely voters from all states. Interviews were conducted with 941 respondents on landline telephones and 276 on cellular phones.
Likely voters completed the entire survey; the balance of the sample completed a shorter version of the questionnaire.
Digits in the phone numbers dialed were generated randomly to reach households with unlisted and listed landline and cell phone numbers.
Interviews were conducted in both English and Spanish.
As is done routinely in surveys, results were weighted, or adjusted, to ensure that responses accurately reflect the population's makeup by factors such as age, sex, education, and race. In addition, the weighting took into account patterns of phone use — landline only, cell only and both types — by region.
No more than one time in 20 should chance variations in the sample cause the results to vary by more than plus or minus 2.8 percentage points from the answers that would be obtained if all people in the U.S. were polled. The margin of sampling error is plus or minus 3.4 percentage points for likely voters.
There are other sources of potential error in polls, including the wording and order of questions.
The questions and results for this poll are available at http://www.ap-gfkpoll.com.