TABLE 2.

Analysis of variances (ANOVA) for the quadratic model.

Source	Sum of squares	df	Mean square	F-value	P-value
Model	271.26	14	19.38	54.24	<0.0001	Significant
X1-Proportion of material	199.02	1	199.02	557.10	<0.0001
X2-Concentration of alcohol	12.97	1	12.97	36.31	<0.0001
X3-Extraction time	0.8836	1	0.8836	2.47	0.1366
X4-Power	0.1778	1	0.1778	0.4977	0.4913
X1X2	0.6360	1	0.6360	1.78	0.2020
X1X3	0.5738	1	0.5738	1.61	0.2244
X1X4	0.0564	1	0.0564	0.1579	0.6967
X2X3	0.0743	1	0.0743	0.2079	0.6550
X2X4	2.83	1	2.83	7.92	0.0131
X3X4	0.0018	1	0.0018	0.0051	0.9443
${\text{X}}_1^2$	0.0273	1	0.0273	0.0765	0.7859
${\text{X}}_2^2$	0.0001	1	0.0001	0.0002	0.9893
${\text{X}}_3^2$	4.70	1	4.70	13.16	0.0025
${\text{X}}_4^2$	0.1742	1	0.1742	0.4875	0.4957
Residual	5.36	15	0.3572
Lack of Fit	3.57	10	0.3569	0.9974	0.5362	Not significant
Pure error	1.79	5	0.3579
Cor total	276.61	29
Fit of the model	Adeq precision		Adjusted R2		Predicted R2
	30.574		0.9625		0.9160