Random Digit Dialing (RDD)
RDD generates random samples of telephone numbers for public opinion surveys. Random digit dialing has the advantage that it includes unlisted numbers that would be missed if the numbers were selected from a phone book. RDD sampling helps reduce non-coverage bias because all telephone households have an equal and representative chance of being interviewed. RDD samples are completely representative of the sampling universe, or frame, and can be “defended” from a methodological standpoint. RDD samples are less expensive than Listed but they are less efficient.