Over a period of years, a toothpaste has received a mean rating of 5.9, on a 7-p

Question

Over a period of years, a toothpaste has received a mean rating of 5.9, on a 7-point scale, for overall customer satisfaction with the product. Because of a minor unadvertised change in the product, there is concern that the customer satisfaction may have changed. Suppose the satisfaction ratings from a sample of 60 customers have a mean of 5.60 and a standard deviation of .87. Do these data indicate that the mean satisfaction rating is differnt from 5.9? Test a = .05. What is the p-value for the test?

Explanation / Answer

Use a t-test. You can find detailed information and formulas here: http://en.wikipedia.org/wiki/Student%27s_t-test T = (x-u)/(s*n(-1/2)) In your case: T = (5.6-5.9)/(0.87*60^(-1/2) T = -2.67 Because the absolute value of T is greater than 2, you know that the new customer satisfaction rating is statistically significantly different from the previous rating at a 0.05 level. This does not necessarily imply that the change caused the drop in customer satisfaction.

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