Table 3.

Analysis of variance of 2nd order model.

Source	Sum of squares	Degrees of freedom	Mean square	F value	P value	Remark
Model	42.35	9	4.71	405.10	<0.0001	Significant
Linear
X1	31.62	1	31.62	2722.20	<0.0001
X3	4.39	1	4.39	377.56	<0.0001
X4	3.29	1	3.29	283.48	<0.0001
X2	0.34	1	0.34	29.37	<0.0001
Interaction
X1X3	0.28	1	0.28	24.08	0.0001
X3X4	0.10	1	0.10	8.80	0.0086
X2X4	0.09	1	0.09	7.65	0.0132
Quadratic
$${\mathrm{X}}_1^2$$	0.43	1	0.43	37.41	<0.0001
$${\mathrm{X}}_3^2$$	0.08	1	0.08	6.84	0.0181
Residual	0.20	17	0.01
Lack of fit	0.16	13	0.01	1.37	0.4111	Not significant
Pure error	0.04	4	9.03 × 10−3
R2					0.9954
Adj-squared					0.9929
Pre R2					0.9884
Adequate precisior					69.64
C.V.					1.54