- Random digit dialing
Random digit dialing (RDD) is a method for selecting people for involvement in telephone
statistical survey s by generatingtelephone number s at random. Random digit dialing has the advantage that it includes unlisted numbers that would be missed if the numbers were selected from aphone book . In populations where there is a hightelephone -ownership rate, it can be a cost efficient way to get complete coverage of a geographic area.RDD is widely used for statistical surveys, including
election opinion polling [cite paper|url=http://bbs.vcsnet.com/pdf/RegistrationBasedSampling.pdf|title=Enough Already with Random Digit Dialing: A Proposal to Use Registration-Based Sampling to Improve Pre-Election Polling|author=Donald P. Green, Alan S. Gerber|date=2002-05-05] and selection ofexperimental control groups [cite paper|url=http://aje.oxfordjournals.org/cgi/content/abstract/135/2/210|title=Evaluation of Random Digit Dialing as a Method of Control Selection in Case–Control Studies|author=Sara H. Olson, Jennifer L. Kelsey, et al|date=1992-01-15] .An important consideration in random digit dialing surveys is bias introduced by non-responders. Non-response bias can be a problem if responders differ from non-responders for the measured variables. For example, nonresponders may not have been contacted because they work multiple minimum-wage jobs. [cite paper|url=http://www.responsivemanagement.com/download/reports/Nonresponse.pdf|title=Nonresponse|author=Peter E. De Michele|publisher=Responsive Management] Various techniques are used to reduce the non-response rate, such as multiple call attempts, monetary incentives, advance letters, and leaving messages on answering machines, because reducing the non-response rate may directly reduce non-response bias. [cite paper|url=http://www.bls.gov/ore/pdf/st030290.pdf|title=Do Current Methods Used To Improve Response To Telephone Surveys Reduce Nonresponse Bias?|author=Roberta L. Sangster] In addition, when trying to calculate total error estimates, response rate calculations can be imprecise because it can be difficult to determine whether certain telephone numbers are interviewable. [cite paper|url=http://www.bls.gov/ore/pdf/st020400.pdf|title=Calling Effort and Nonresponse for Telephone Panel Surveys|date=2003-06-10|author=Roberta L. Sangster] [cite paper|url=http://www.amstat.org/sections/srms/proceedings/papers/1997_121.pdf|title=Response Rates in Random Digit Dialing (RDD) Telephone Surveys|date=1997|author=James T. Massey, Dan O'Connor, Karol Krotki]
When the desired coverage area matches up closely enough with
country code s andarea code s, random digits can be chosen within the desired area codes. In cases where the desired region doesn't match area codes (for instance,electoral district s), surveys must rely on telephone databases, and must rely on self-reported address information for unlisted numbers. Increasing use of mobile phones (although there are currently techniques which allow infusion of wireless phones into the RDD sampling frame), number portability, andVoIP have begun to decrease the ability for RDDee also
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Autodialer References
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