Question: The list of individuals from which a sample is actually selected is called sampling frame. Ideally, the frame should list every individual in the population but in practice this is often difficult. A frame that leaves out part of the population is a common source of undercoverage.

(a) Suppose that a sample of households in a community is selected at random from the telephone directory. What houses are omitted from this sample?

(b) It is usual in telephone surveys to use random digit dialing equipment that selects the last four digits from a telephone directory. What households from (a) will be now included?