Table 2.

Test of significance for the regression coefficient^a.

Source	Sum of Squares	Degree of Freedom	Mean Square	F-Value	p-Value
Model b	41.39	9	4.60	29.21	<0.0001
X1	7.08	1	7.08	44.97	0.0003
X2	0.15	1	0.15	0.94	0.3637
X3	1.58	1	1.58	10.02	0.0158
X1 X2	0.25	1	0.25	1.58	0.2494
X1 X3	0.24	1	0.24	1.53	0.2561
X2 X3	2.67	1	2.67	16.93	0.0045
X1 2	1.97	1	1.97	12.50	0.0095
X2 2	0.051	1	0.051	0.33	0.5860
X3 2	26.60	1	26.60	168.95	<0.0001
Residual	1.10	7	0.16
Lack of fit	0.45	3	0.15	0.93	0.5024
Pure error	0.65	4	0.16
Cor total	42.49	16

^a: The results were obtained with Design Expert 8.0 software; ^b: X₁ is the microwave irradiation time (min), X₂ is the liquid–solid ratio (mL/g), and X₃ is the microwave irradiation power (W).