From two USA Today/Gallup polls, we found information about Americans' approval of government bailouts to two of the Big Three U.S. automakers. The question asked was, "Do you approve or disapprove of the federal loans given to General Motors and Chrysler last year to help them avoid bankruptcy?" In a February 2009 poll of 1007 national adults, 41% said they approved, and in a March 2009 poll of 1007 national adults, 39% said they approved. At the 5% significance level, do the data provide sufficient evidence to conclude that a difference exists in the approval percentages of all U.S. adults between the two months?
a. Use the two-proportions z-test (Procedure 11.3 on page 463).
b. Use the chi-square homogeneity test.
c. Compare your results in parts (a) and (b).
d. What does this exercise illustrate?