In evaluating different measuring instruments, one must first determine whether there is a systematic difference between the instruments. Lenses with several different powers were measured once each by two different instruments. The measurement differences (Instrument A €“ Instrument B) were recorded.The measurement units have been coded for proprietary Dreasons.

Does there appear to be a systematic difference between the two instruments?
a. Describe the data using a histogram and one other graph.
b. Find the mean and the standard deviation.
c. Are the assumptions required for making inferences satisfied? Explain.
d. Using a 95% confidence interval, estimate the population mean of the differences.
e. Is there any evidence of a difference? Explain.

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