Dear Akanbi

I think it intensely depends on type of your variables(and i think in the majority of cases it wouldn't be correct)! I've already approached with such a problem in designing the Concentration variable (for example) and it was obviously wrong.

you can message me if you have any other problems in designing thorough design expert software.

Regards

"alpha" is a probability. It can not be negative. Hence, it is not possible to have negative values for "alpha".

Sidharth Gautam Please clarify the above question.

A Box-Wilson Central Composite Design, commonly called 'a central composite design,' contains an imbedded factorial or fractional factorial design with center points that is augmented with a group of 'star points' that allow estimation of curvature. If the distance from the center of the design space to a factorial point is ±1 unit for each factor, the distance from the center of the design space to a star point is |α| > 1. The precise value of α depends on certain properties desired for the design and on the number of factors involved.

for in-depth explanation refer : https://www.itl.nist.gov/div898/handbook/pri/section3/pri3361.htm