Table 3.

Regression coefficient and their significance of the quadratic model.

Term	Coefficient		Standard Error		T-Value		p-Value
	FFAs	Yield	FFAs	Yield	FFAs	Yield	FFAs	Yield
Constant	1.639	24.529	0.123	0.766	13.29	32.04	0.000	0.000
X 1	−3.559	2.356	0.082	0.508	−43.51	4.64	0.000	0.001
X 2	−0.089	1.409	0.082	0.508	−1.09	2.77	0.303	0.020
X 3	0.783	−1.094	0.082	0.508	9.57	−2.15	0.000	0.057
X 1 2	2.935	−0.370	0.079	0.494	36.85	−0.75	0.000	0.471
X 2 2	0.087	−0.020	0.079	0.494	1.09	−0.04	0.301	0.968
X 3 2	0.414	0.119	0.079	0.494	5.20	0.24	0.000	0.814
X 1 X 2	0.085	−1.648	0.107	0.664	0.79	−2.48	0.447	0.032
X 1 X 3	−0.794	−0.017	0.107	0.664	−7.43	−0.03	0.000	0.980
X 2 X 3	0.068	0.073	0.107	0.664	0.64	0.11	0.537	0.914