For Exercises 13.18 to 13.20, see pages 670–671; for 13.21 to 13.23, see page 677; for 13.24, see page 679.

Question 13.18

13.18 Percent of Canadian Internet users.

Below are data on the time series of the percent of Canadians using the Internet for eight consecutive years ending in 2013.13

Year 2006 2007 2008 2009 2010 2011 2012 2013
Percent (%) 72.4 73.2 76.7 80.3 80.3 83.0 83.0 85.8

We usually want a time series longer than just eight time periods, but this short series will give you a chance to do some calculations by hand. Hand calculations take the mystery out of what computers do so quickly and efficiently for us.

  1. Make a time plot of these data.
  2. Using the following summary information, calculate the least-squares regression line for predicting the percent of Canadians using the Internet. The variable simply takes on the values 1, 2, 3, …, 8 in time order.

    671

    Variable Mean Standard deviation Correlation
    4.5 2.44949 0.977
    Percent users 79.3375 4.82847
  3. Sketch the least-squares line on your time plot from part (a). Does the linear model appear to fit these data well?
  4. Interpret the slope in the context of the application.