The National Quality Research Center at the University of Michigan provides a quarterly measure of consumer opinions about products and services (The Wall Street Journal, February 18, 2003). A survey of 10 restaurants in the Fast Food/ Pizza group showed a sample mean customer satisfaction index of 71. Past data indicate that the population standard deviation of the index has been relatively stable with σ=5.
a. Explain what assumption the researcher should be willing to make if a margin of error is desired.
b. Using 95% confidence, determine the margin of error.
c. Determine the margin of error if 99% confidence is desired.
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The solution shows how to work with margin of error and confidence.