Table 2.

Results of the ANOVA to the response surface quadratic model.

Source	df	Sum of Squares	Mean Square	F-Value	p-Value
Model	14	425.74	30.41	279.18	<0.0001 **
${\mathrm{X}}_1$	1	81.96	81.96	752.39	<0.000 1**
${\mathrm{X}}_2$	1	55.72	55.72	511.57	<0.0001 **
${\mathrm{X}}_3$	1	38.03	38.03	349.11	<0.0001 **
${\mathrm{X}}_4$	1	14.49	14.49	133.05	<0.0001 **
${\mathrm{X}}_1{\mathrm{X}}_2$	1	2.88	2.88	26.45	0.0001 **
${\mathrm{X}}_1{\mathrm{X}}_3$	1	0.26	0.26	2.41	0.1413
${\mathrm{X}}_1{\mathrm{X}}_4$	1	0.18	0.18	1.68	0.2148
${\mathrm{X}}_2{\mathrm{X}}_3$	1	0.51	0.51	4.73	0.0461 *
${\mathrm{X}}_2{\mathrm{X}}_4$	1	0.052	0.052	0.48	0.5012
${\mathrm{X}}_3{\mathrm{X}}_4$	1	1.25	1.25	11.46	0.0041 **
${\mathrm{X}}_1{}^2$	1	185.28	185.28	1701.00	<0.0001 **
${\mathrm{X}}_2{}^2$	1	73.35	73.35	673.40	<0.0001 **
${\mathrm{X}}_3{}^2$	1	11.11	11.11	102.04	<0.0001 **
${\mathrm{X}}_4{}^2$	1	6.83	6.83	62.72	<0.0001 **
Residual	15	1.63	0.11
Lack od fit	10	1.41	0.14	3.21	0.1050
Pure error	5	0.22	0.044
Cor total	29	427.37
R2 = 0.9962
Adj-R2 = 0.9926

Note: * p < 0.05 significant, ** p < 0.01 highly significant.