Table 3.

Analysis of variance for the experimental results of zerumbone content from Z. zerumbet rhizomes

Parameter	Estimated coefficient	Standard error	Degree of freedom	Sum of squares	F value	Prob > F
Model intercept B0	5.51	0.084	14	3.95	13.38	0.0001
Linear
X1	0.14	0.042	1	0.25	11.74	0.005
X2	0.017	0.042	1	0.00343	0.16	0.693
X3	−0.055	0.042	1	0.037	1.77	0.211
X4	0.27	0.042	1	0.085	40.46	0.0001
Quadratic
$X_1^2$	−0.41	0.063	1	0.89	42.02	0.0001
$X_2^2$	−0.096	0.063	1	0.05	2.35	0.1513
$X_3^2$	−0.085	0.063	1	0.039	1.84	0.2001
$X_4^2$	−0.39	0.063	1	0.081	38.52	0.0001
Interaction
X1X2	0.12	0.073	1	0.057	2.71	0.1259
X1X3	0.14	0.073	1	0.079	3.74	0.077
X1X4	−0.31	0.073	1	0.039	18.45	0.001
X2X3	0.45	0.073	1	0.08	37.78	0.0001
X2X4	−0.13	0.073	1	0.072	3.42	0.0894
X3X4	−0.061	0.073	1	0.015	0.69	0.4212
Lack of fit			10	0.23	2.15	0.3596
Pure error			2	0.022
Residual			12	0.025
R2 adjusted					0.875
R2					0.939
C.V.%	2.86
Corr. total			26	4.21

X₁, ethanol concentration; X₂, microwave power; X₃, irradiation time; X₄, liquid-to-solid ratio