Digits in the phone numbers dialed were generated randomly to reach households with unlisted and listed landline and cellphone numbers.
Interviews were conducted in 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, region and race. In addition, the weighting took into account patterns of phone use — landline only, cellphone only and both.
No more than 1 time in 20 should chance variations in the sample cause the results to vary by more than plus or minus 3.6 percentage points from the answers that would be obtained if all adults age 40 or older in the U.S. were polled.
The survey was conducted with funding from The SCAN Foundation.
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 .