From the Web site of Gallup, Inc., we found polls regarding Americans' approval of how the president is handling foreign affairs. In two particular polls, the question asked was, "Do you approve of the way Barack Obama is handling foreign affairs?" In a February 2009 poll of 1007 national adults, 54% said they approved, and in a March 2009 poll of 1007 national adults, 61% 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?