3.
Production
Process Characterization
3.5. Case Studies 3.5.2. Machine Screw Case Study


Analysis of Variance Using All Factors 
We can confirm our interpretation of the box plots by running
an analysis of variance when all four factors are included.
Source DF Sum of Mean F Statistic Prob > F Squares Square  Machine 2 0.000111 0.000055 29.3159 1.3e11 Day 2 0.000004 0.000002 0.9884 0.37 Time 1 0.000002 0.000002 1.2478 0.27 Sample 9 0.000009 0.000001 0.5205 0.86 Residual 165 0.000312 0.000002  Corrected Total 179 0.000437 0.000002  
Interpretation of ANOVA Output 
We fit the model
Only the machine factor is statistically significant. This confirms what the box plots in the previous section had indicated graphically. 

Analysis of Variance Using Only Machine 
The previous analysis of variance indicated that only the
machine factor was statistically significant. The following
table displays the ANOVA results using only the machine factor.
Source DF Sum of Mean F Statistic Prob > F Squares Square  Machine 2 0.000111 0.000055 30.0094 6.0E12 Residual 177 0.000327 0.000002  Corrected Total 179 0.000437 0.000002 

Interpretation of ANOVA Output 
At this stage, we are interested in the level means for the
machine variable. These can be summarized in the following
table.


Model Validation 
As a final step, we validate
the model by generating a
4plot of the residuals.
The 4plot does not indicate any significant problems with the ANOVA model. 