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Table 4 Estimates, standard errors, and variance inflation factors (VIF) of parameters of the fitted split-plot CCD model

From: Optimization of phenol adsorption from synthetic wastewater by synthesized BiFeO3 perovskite material, using split-plot central composite design

Source Coefficient estimate Standard error VIF
Intercept 87.56 2.82  
Whole-plot terms:
a-pH 3.97 1.89 1
a2  − 14.60 1.63 1.04
Subplot terms:    
B-Tim 4.40 2.26 1
C-Dosage  − 1.30 2.26 1
aB 0.02 2.99 1
aC  − 5.95 2.99 1
BC 2.06 2.99 1
B2  − 11.27 2.01 1.02
C2  − 10.46 2.01 1.02