Table 5 Regression coefficients for adsorption of copper by DNES–CH composite
Model term Coefficient estimate Standard error  F value  p value
Intercept 95.25 1.06 46.25 <0.0001
X 1 −1.74 0.55 9.87 0.0056
X 2 0.56 0.55 1.03 0.3240
X 3 −0.089 0.55 0.026 0.8739
X 1 X 2 −5.84 0.68 74.48 <0.0001
X 1 X 3 −2.09 0.68 9.59 0.0062
X 2 X 3 −1.00 0.68 2.19 0.1563
X 12 −16.11 0.93 301.46 <0.0001
X 22 −2.29 0.93 6.11 0.0236
X 32 −0.82 0.93 0.78 0.3898
All the linear, interaction and squared terms are significant (p < 0.5), excluding linear X 3