A retail computer dealer is trying to decide between two methods for servicing customers’ equipment. The first method emphasizes preventive maintenance; the second emphasizes quick response to problems. The dealer serves samples of customers by one of the two methods in a random fashion. After 6 months, the dealer finds that 171 of 200 customers serviced by the first method are very satisfied with the service as compared to 155 of 200 customers served by the second method.
a. Test the research hypothesis that the population proportions of very satisfied customers are different for the two methods. Use a = .05. Carefully state your conclusion.
b. Compute a confidence interval for the difference in the proportions. Does the confidence interval provide the same conclusion about the difference in proportions as your test in part (a)? Justify your answer.