Table 6.
The variance analysis results of the quadratic regression model
| Source | Sum of squares | Degree of freedom | Mean square | F value | P value | Significant |
|---|---|---|---|---|---|---|
| Model | 24.18 | 14 | 1.73 | 9.47 | ˂.0001 | ** |
| X 1–X 1 | 6.54 | 1 | 6.54 | 35.84 | ˂.0001 | ** |
| X 2–X 2 | 0.87 | 1 | 0.87 | 4.20 | .0623 | |
| X 3–X 3 | 0.44 | 1 | 0.44 | 2.43 | .1416 | |
| X 4–X 4 | 0.67 | 1 | 0.67 | 3.70 | .0751 | |
| X 1 X 2 | 0.23 | 1 | 0.23 | 1.24 | .2834 | |
| X 1 X 3 | 7.51E‐03 | 1 | 7.51E‐03 | 0.04 | .8421 | |
| X 1 X 4 | 2.23E‐03 | 1 | 2.23E‐03 | 0.01 | .9134 | |
| X 2 X 3 | 0.48 | 1 | 0.48 | 2.63 | .1273 | |
| X 2 X 4 | 0.39 | 1 | 0.39 | 2.13 | .1661 | |
| X 3 X 4 | 0.10 | 1 | 0.10 | 0.55 | .4700 | |
| X 1 2 | 4.72 | 1 | 4.72 | 25.90 | .0002 | |
| X 2 2 | 1.82 | 1 | 1.82 | 9.96 | .0070 | |
| X 3 2 | 1.78 | 1 | 1.78 | 9.79 | .0074 | |
| X 4 2 | 0.60 | 1 | 0.60 | 3.28 | .0915 | |
| Total error | 2.55 | 14 | 0.18 | |||
| Lack of fit | 2.26 | 8 | 0.28 | 5.80 | .0530 | |
| Pure error | 0.29 | 6 | 0.05 | |||
| Total SS | 26.73 | 28 |
Predicted R 2 = .9045 CV = 9.95%.