10.23 In tough economic times, the business staff at
magazines are challenged to sell advertising space in their
publications. Thus, one indicator of a weak economy is the
decline in the number of “ad pages” that magazines have
sold. The file contains the number of ad pages
found in the May 2008 and May 2009 issues of 12 men’s
magazines. (Data extracted from W. Levith, “Magazine
Monitor,” Mediaweek, April 20, 2009, p. 53.)
a. At the 0.05 level of significance, is there evidence that
the mean number of ad pages was higher in May 2008
than in May 2009?
b. What assumption is necessary about the population
distribution in order to perform this test?
c. Use a graphical method to evaluate the validity of the
assumption in (b).
d. Construct and interpret a 95% confidence interval
estimate of the difference in the mean number of ad pages
in men’s magazines between May 2008 and May 2009.