A computer lab at the University of Oklahoma is open 24 hours a day, 7 days a week. In Production and Inventory Management Journal (3rd Quarter, 1999), S. Barman investigated whether computer usage differed significantly (1) among the 7 days of the week and (2) among the 24 hours of the day. Using student log-on records, data on hourly student loads (number of users per hour) were collected during a 7-week period. A factorial ANOVA was employed with the results presented in the table.

a. Is this an observational or a designed experiment? Explain.

b. What are the two factors of the experiment and how many levels of each factor are used?

c. This is an a × b factorial experiment. What are a and b?

d. Specify the null and alternative hypotheses that should be used to test for an interaction effect between the two factors of the study.

e. Conduct the test of part d using α = .05. Interpret your result in the context of the problem.

f. If appropriate, conduct main effects tests for both day and time. Use α = .05. Interpret your results in the context of the problem.

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source df SS MS F p-Value Day Time 18732.13 3122.02 68.39 .0001 23 164629.86 7157.82 156.80 .0001 Day x Time 138 7685.22 55.69 1.22 .0527