3.40 The report “Wireless Substitution: Early Release of Estimates from the National Health Interview Survey” (Center for Disease Control, 2009) gave the following estimates of the percentage of homes in the United States that had only wireless phone service at 6-month intervals from June 2005 to December 2008.

Date Percent with Only Wireless Phone Service June 2005 7.3 December 2005 8.4 June 2006 10.5 December 2006 12.8 June 2007 13.6 December 2007 15.8 June 2008 17.5 December 2008 20.2

a. Construct a time series plot for these data and describe the trend in the percent of homes with only wireless phone service over time. (Hint: See Example 3.22.)

b. Has the percent increased at a fairly steady rate?