An article in the Journal of Testing and Evaluation (1988, Vol. 16, pp. 508€“515) investigated the effects of cyclic loading frequency and environment conditions on fatigue crack growth at a constant 22 MPa stress for a particular material. The data follow. The response variable is fatigue crack growth rate.

(a) Is there indication that either factor affects crack growth rate? Is there any indication of interaction? Use α = 0.05.

(b) Analyze the residuals from this experiment.

(c) Repeat the analysis in part (a) using ln(y) as the response. Analyze the residuals from this new response variable and comment on the results.

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Environment Salt H20 Air Н,о 2,29 2.47 2.06 10 1.90 1.93 2.05 2.48 2.12 2.23 2.03 1.75 2.06 1 2.65 2.68 3.20 3.18 3.10 3.24 Frequency 2.06 2.38 3.96 3.98 3.24 3.64 0.1 2.24 11.00 9.96 2.71 2.81 11.00 9.06 10.01 9.36 2.08 11.30 10.40