In Myers, Montgomery, and Anderson-Cook (2009), a scenario is discussed involving an auto bumper plating process. The response is the thickness of the material. Factors that may impact the thickness include amount of nickel (A) and pH (B). A two-factor experiment is designed. The plan is a completely randomized design in which the individual bumpers are assigned randomly to the factor combinations. Three levels of pH and two levels of nickel content are involved in the experiment. The thickness data, in cm × 10-3, are as follows:
|
Nickel Content
(grams)
|
|
pH
|
|
|
|
5.5
|
|
|
18
|
250
|
211
|
221
|
|
195
|
172
|
150
|
|
188
|
165
|
170
|
|
10
|
115
|
88
|
69
|
|
165
|
112
|
101
|
|
142
|
108
|
72
|
(a) Display the analysis-of-variance table with tests for both main effects and interaction. Show P-values.
(b) Give engineering conclusions. What have you learned from the analysis of the data?
(c) Show a plot that depicts either a presence or an absence of interaction.