The manager of a manufacturing plant knows that the output of a production line depends on two factors:

• Which of two supervisors is in charge of the line

• Which of three shifts—day, swing, or night—is being measured The manager suspects that the two supervisors may work differently depending on the particular shift they are working—perhaps the first supervisor is more effective in the morning, and the second is more effective during the night shift. That is, there may be an interaction between supervisor and shift! The supervisors are each observed on three randomly selected days for each of the three different shifts, resulting in n52(3)(3)518 responses. The average outputs for the three shifts are shown in Table 11.4 for each of the supervisors.

Look at the relationship between the two factors in the line chart for these means, shown in Figure 11.11. Notice that supervisor 2 always produces a higher output, regardless of the

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Table 11.4 Average Outputs for Two Supervisors on Three Shifts Shift Supervisor Day Swing Night 1 487 498 550 2 602 602 637