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How the AP-NORC poll on the impact of 9/11 was conducted
The Associated Press-NORC Poll on the impact of the Sept. 11 attacks was conducted from July 28 to Aug. 15 by the AP-NORC Center for Public Affairs Research. It is based on landline and cellular telephone interviews with a nationally representative random sample of 1,087 adults. Interviews were conducted by NORC at the University of Chicago and included 773 respondents on landline telephones and 314 on cellular phones.
Digits in the phone numbers dialed were generated randomly to reach households with unlisted and listed landline and cellphone 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, cellphone only and both ' by region.
No more than 1 time in 20 should chance variations in the sample cause the results to vary by more than plus or minus 4.1 percentage points from the answers that would be obtained if all adults in the U.S. were polled.
There are other sources of potential error in polls, including the wording and order of questions.
The questions and results are available at http://www.apnorc.org .