Table 4. Analysis of variance (ANOVA) for the quadratic model.

Source	Sum of squares	Degree of freedom	Mean of square	F value	P value
Model	328.1976	9	36.4664	32.8442	<0.0001
x 1	55.1439	1	55.1439	49.6665	<0.0001
x 2	10.1688	1	10.1688	9.1587	0.0128
x 3	8.7309	1	8.7309	7.8636	0.0187
x 1 x 2	2.1841	1	2.1841	1.9671	0.1910
x 1 x 3	2.1218	1	2.1218	1.9110	0.1969
x 2 x 3	1.4450	1	1.4450	1.3015	0.2805
x 1 2	221.6356	1	221.6356	199.6204	<0.0001
x 2 2	10.5680	1	10.5680	9.5183	0.0115
x 3 2	41.6273	1	41.6273	37.4924	0.0001
Residual	11.1029	10	1.1103
Lack of fit	6.2947	5	1.2589	1.3092	0.3874
Pure error	4.8081	5	0.9616
Total	339.3005	19

R² = 96.73%; Adj R² = 93.78%.

P value less than 0.05 indicates that the model terms are significant.

P value less than 0.01 indicates that the model terms are highly significant.