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Unformatted text preview: Failure to use random sampling often results in bias , or systematic errors in the way the sample represents the population . Voluntary response samples , in which the respondents choose themselves, are particularly prone to large bias . In human populations , even random samples can suffer from bias due to undercoverage or nonresponse , from response bias , or from misleading results due to poorly worded questions. Sample surveys must deal expertly with these potential problems in addition to using a random sampling design. Most national sample surveys are carried out by telephone,using random digit dialing to choose residential telephone numbers at random. Call screening is increasing nonresponse to such surveys, and the rise of cell-phone-only households is increasing undercoverage ....
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- Fall '11