An article in the IEEE Transactions on Components, Hybrids, and Manufacturing Technology (Vol. 15, No. 2, 1992, pp. 146€“153) describes an experiment in which the contact resistance of a brake-only relay was studied for three different materials (all were silver-based alloys). The data are as follows.

(a) Does the type of alloy affect mean contact resistance? Use a = 0.01.
(b) Use Fisher€™s LSD method to determine which means differ.
(c) Find a 99% confidence interval on the mean contact resistance for alloy 3.
(d) Analyze the residuals for this experiment.

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Alloy Contact Resistance 95 97 98 99 99 99 99 95 98 94 102 102 105 99 104 102 111 103 100 103 119 130 132 136 141 172 145 150 144 135 2.