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Quality Progress, February 2005, reports on the results achieved by Bank of America in improving customer satisfaction and customer loyalty by listening to the “voice of the customer.” A key measure of customer satisfaction is the response on a scale from 1 to 10 to the question: “Considering all the business you do with Bank of America, what is your overall satisfaction with Bank of America?” Suppose that a random sample of 350 current customers results in 195 customers with a response of 9 or 10 representing “customer delight”. Find a 95 percent confidence interval for the true proportion of all current Bank of America customers who would respond with a 9 or 10.

Are we 95 percent confident that this proportion exceeds .48, the historical proportion of customer delight for Bank of America?

  • Statistics -

    Use a proportional confidence interval formula.

    CI95 = p + or - 1.96(√pq/n)
    ...where p = 195/350 (convert to a decimal), q = 1 - p, n = 350, and + or - 1.96 represents the 95% interval using a z-table.

    I'll let you take it from here.

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