IV.31. When shall we call you? In Exercise IV.11, we learned of a study that dialed telephone numbers at random during two periods of the day. Of 2304 numbers called on weekday mornings, 1313 answered. Of 2454 calls on weekday evenings, 1840 were answered.

  1. (a) Make a two-way table of time of day versus answered or not. What percentage of calls were answered in each time period? (Hint: See pages 572–573.)

  2. (b) It should be obvious that there is a highly significant relationship between time of day and answering. Why? (Hint: See pages 572–576.)

  3. (c) Nonetheless, carry out the chi-square test. What do you conclude? (Hint: See pages 577–581.)

IV.31 (a) Morning calls: 1313/2304 = 57.0%; Evening calls: 1840/2454 = 75.0%. (b) The percent of calls answered in the evening versus morning are very different. (c) X2 = 172.080 with df = 1, which is highly significant. There is a relationship between the time at which a call was placed and whether it was answered.

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