Cotton percentage in Exercise 13-5. Use α = 0.05.

(a) Apply Fisher€™s LSD method with α = 0.05 and determine which levels of the factor differ.

(b) Use the graphical method to compare means described in this section and compare your conclusions to those from Fisher€™s LSD method.

Exercise 13-5

In Design and Analysis of Experiments, 8th edition (John Wiley & Sons, 2012), D. C. Montgomery described an experiment in which the tensile strength of a synthetic fi ber was of interest to the manufacturer. It is suspected that strength is related to the percentage of cotton in the fiber. Five levels of cotton percentage were used, and five replicates were run in random order, resulting in the following data.

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Observations Cotton Percentage 2 3 15 15 11 20 12 17 12 18 18 25 14 18 18 19 19 30 19 25 22 19 23 35 10 11 15 11