1. Chilton Research Services. “Continuous Tracking Studies via WATS Lines and Personal Interviewing,”. Report presented to the Advertising Research Foundation, 13th Annual Conference, Chilton Research Services. Phila., Pa.
2. Telephone directory samples and random telephone number generation
3. Hansen, Morris H., Hurwitz, William N. and Madow, William G. 1953.Sample Survey Methods and Theory, 1New York: John Wiley & Sons.
4. Random-Digit Dialing as a Method of Telephone Sampling
5. National Estimates of Nonlisted Telephone Households and Their Characteristics