For Exercises 3.17 and 3.18 see page 130; for 3.19 and 3.20, see pages 131–132; for 3.21 and 3.22, see page 134; for 3.23 and 3.24, see page 136; and for 3.25, see page 138.

Question 3.25

3.25 Random digit dialing.

The list of cases from which a sample is actually selected is called the sampling frame. Ideally, the frame should include every case 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.

  1. Suppose that a sample of households in a community is selected at random from the telephone directory. What households are omitted from this frame? What types of people do you think are likely to live in these households? These people will probably be underrepresented in the sample.
  2. It is usual in telephone surveys to use random digit dialing equipment that selects the last four digits of a telephone number at random after being given the exchange (the first three digits). Which of the households that you mentioned in your answer to part (a) will be included in the sampling frame by random digit dialing?

3.25

(a) Households not listed in the telephone directory are omitted. They may not own a phone or choose to have their number unlisted. (b) Random digit dialing would include those that are unlisted but own a phone.