A researcher wished to estimate the difference between the proportion of users of two shampoos who are satisfied with the product. In a sample of 400 users of Shampoo A taken by this researcher, 78 said they are satisfied. In another sample of 500 users of Shampoo B taken by the same researcher, 92 said they were satisfied.
Construct a 90% confidence interval for the true difference between the two population proportions.
Based on your answer in (a), what would be your response at ".1 to the claim that there is no difference in customer satisfaction between the two shampoos?