Disk drive service. The staff of u service center for electronic equipment includes three technicians who specialize in repairing three widely used makes of disk drives for desktop computers. It was desired to study the effects of technician (factor A) and make of disk drive (factor B) on the service time. The data that follow show the number of minutes required to complete the repair job in a study where each technician was randomly assigned to five jobs on each make of disk drive.
a. Obtain the fitted values for ANOVA model (19.23).
b. Obtain the residuals.
c. Plot the residuals against the fitted values. What departures from ANOVA model (19.23) can be studied from this plot? What are your findings?
d. Prepare a normal probability plot of the residuals. Also obtain the coefficient of correlation between the ordered residuals and their expected values under normality. Does the normality assumption appear to be reasonable here?
e. The observations for each treatment were obtained in the order shown. Prepare residual sequence plots and analyze them. What are your findings?