Table 3.

Analysis of variables based on Plackett-Burman design.

Variables	Effect	Coefficient	T-value	P-value
Intercept		2.2867	149.56	< 0.0001
X1	0.1884	0.0942	6.16	0.0016
X2	0.0236	0.0118	0.77	0.4759
X3	-0.1318	-0.0659	-4.31	0.0076
X4	0.1667	0.0833	5.45	0.0028
X5	0.1456	0.0728	4.76	0.0051
X6	0.1158	0.0579	3.79	0.0128