In tough economic times, magazines and other media have trouble selling advertisements. Thus, one indicator of a weak economy is a reduction in the number of magazine pages devoted to advertisements. The file AD PAGES contains the number of pages devoted to advertisements in May 2008 and May 2009 for 12 men's magazines.
a. At the 0.05 level of significance, is there evidence that the mean number of pages devoted to advertisements in men's magazines 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 pages devoted to advertisements in men's magazines between may 2008 and May 2009.