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Random Digit Dialling (RDD)

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Random Digit Dialling (RDD)

Random Digit Dialling (RDD) is a common method of selecting people to take part in telephone surveys. The computer based technique picks telephone numbers at random, to provide a representative survey sample.

National lists of telephone area codes, exchanges and individual numbers exit, make sampling for telephone interviews fairly simple.

Random Digit Dialling (RDD) uses a computer programme to dial a random sequence of numbers (this could be a four-digits at random, which are then added to each combination of area code and telephone exchange).  

Random Digit Dialling (RDD) samples can be defined by a variety of geographies, including area code and geography. These samples will often include working, non-working and unassigned numbers, although that can be problematic, in that large numbers might be unassigned or are the wrong type of numbers (could be a business' number rather than a home number). It does however ensure each telephone number has an equal probability of selection.

Using Random Digit Dialling (RDD) has a major advantage over using a telephone directory to identify sample, it includes the unlisted numbers that would be otherwise missed if the numbers were selected from a phone book or phone directory.

It is estimated that five calls must be made to get one working residential number.

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