3.
Production
Process Characterization
3.5. Case Studies 3.5.2. Machine Screw Case Study
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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 1.3e-11 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. |
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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 6.0E-12 Residual 177 0.000327 0.000002 ------------------------------------------------------------------ Corrected Total 179 0.000437 0.000002 |
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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.
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Model Validation |
As a final step, we validate
the model by generating a
4-plot of the residuals.
The 4-plot does not indicate any significant problems with the ANOVA model. |