A type of bias that occurs when some groups in the population are left out of the process of choosing the sample.
Random Digit Dialing
A method of selecting a sample for a telephone survey that involves the generation of random telephone numbers.
A method of contacting people on the phone. Random numbers are dialed, so this allows researchers to sample people with unlisted phone numbers.
A bias that results from systematically excluding certain subsets of the population from the sample. It is not necessarily intentional.