Term

Effect value

Standard error

t –value (13 DF)*

p-value

Average

0.60

0.055

12.0

<0.01

X1

0.26

0.110

2.4

0.03

X2

0.09

0.110

0.8

0.42

X3

-0.02

0.110

-0.2

0.81

X4

0.18

0.110

1.7

0.11

X5

0.21

0.110

2.0

0.07

*DF: Degree of freedom; t - tabulated = ±1.77 for a confidence level of 90% and 13 DF.
Table 4: Effect values and significance tests for the average and main variables effects in relation to Qp for the 25-1 experimental design.