Company:The Pew Research Center for the People & the Press
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Independent opinion research group studying attitudes toward the press, politics and public policy issues.
' About Methodology in Detail The sample for a typical national survey consists of a random digit sample of telephone numbers selected from telephone exchanges in the continental United States. The random digit aspect of the sample is used to avoid "listing" bias and provides representation of both listed and unlisted numbers (including not-yet-listed). The design of the sample ensures this representation by random generation of the last two digits of telephone numbers selected on the basis of their area code, telephone exchange, and bank number. The telephone exchanges are selected with probabilities proportional to their size. The first eight digits of the sampled telephone numbers (area code, telephone exchange, bank number) are selected to be proportionally stratified by county and by telephone exchange within county. That is, the number of telephone numbers randomly sampled from within a given county is proportional to that county's share of telephone numbers '-The Pew Research Center for the People & the Press
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