An online retailer sends many packages to customers. To investigate the quality of shipping, the retailer employed three firms to ship packages. Each firm was given four packages to ship at each of three times of day, morning, afternoon, and evening. The outcome variable was the number of hours elapsed during shipment. The following MINITAB output presents the results.

a. Can you reject the hypothesis of no interactions? Explain.

b. Can the main effect of firm on number of hours elapsed be interpreted? If so, interpret the main effect, using the α = 0.05 level of significance. If not, explain why not.

c. Can the main effect of time of day on number of hours elapsed be interpreted? If so, interpret the main effect, using the α = 0.05 level of significance. If not, explain why not.

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Analysis of Variance for Hours Elapsed Source DF SS MS F P Firm 2 47.494 23.747 4.6546 0.018 Time of day 2 62.779 31.390 6.1526 0.006 Interaction 4 65.170 16.293 4.1735 0.009 Error 27 137.75 5.1019 Total 35 333.19