Table 2.

Analysis of variance (ANOVA) for the fitted quadratic polynomial model

Source	Degree freedom	ER		WAI		TPC		DPPH
		F value	p value	F value	p value	F value	p value	F value	p value
Model	14	10.79	0.0002	8.00	0.0001	5.99	0.0001	7.78	0.0002
$x_1$	1	115.79	< 0.0001	5.55	0.0325	8.19	0.0119	71.95	< 0.0001
$x_2$	1	4.64	0.1026	40.14	< 0.0001	4.74	0.0459	5.01	0.0407
$x_3$	1	0.44	0.0044	42.59	< 0.0001	2.90	0.1092	2.05	0.1732
$x_4$	1	0.68	0.8284	0. 047	0.8305	5.56	0.0323	7.69	0.0142
$x_1{x}_2$	1	1.75	0.1716	0.36	0.5571	0.31	0.5835	4.48	0.0515
$x_1{x}_3$	1	0.016	0.8948	0.79	0.3893	0.51	0.4880	2.12	0.1658
$x_1{x}_4$	1	1.40	0.6762	0.18	0.6746	1.46	0.2454	0.033	0.8588
$x_2{x}_3$	1	0.30	0.7348	0.93	0.3504	1.25	0.2816	0.58	0.4585
$x_2{x}_4$	1	0.45	0.9956	0. 31	0.5885	13.26	0.0024	0.43	0.5198
$x_3{x}_4$	1	3.28	0.3671	0. 57	0.4627	4.18	0.0588	9.581E−003	0.9233
$x_1^2$	1	6.70	0.0218	0.12	0.7302	17.40	0.0008	12.31	0.0032
$x_2^2$	1	0.74	0.5321	0.43	0.5197	20.08	0.0004	1.24	0.2996
$x_3^2$	1	2.00	0.2928	11.37	0.0042	7.26	0.0167	4.53	0.0425
$x_4^2$	1	6.09	0.1735	3.77	0.0712	14.60	0.0017	0.37	0.2507
Lack of fit	10	2.01	0.2283	01.39	0.3758	1.99	0.2318	3.07	0.1136
R 2		0.90		0.88		0.84		0.87
Adjusted R 2		0.86		0.84		0.79		0.86