Table 4. Analysis of variance and regression analyses for the response of the 2⁴ central composite design.

Source of variation

Sum of squares

Degrees of freedom

Mean squares

F_test^a

p-value

 Regression

2.4883

9

0.2765

14.2

<0.00001

 Residual

0.3310

17

0.0195

 Lack of fit

0.2733

15

0.0182

 Pure error

0.0577

2

0.0288

 Total

2.8193