here, in title of Incomplete Factorial Design, it is written that
" it is actually impossible to implement a group that simultaneously has several levels of treatment factors and receives no treatment at all."
But i have not understood, in full factorial design we also allow for a treatment combination where all factors are absent, i.e , treatment combination $(1)$, and it works as control.
Where is the difference between the control of full factorial design and incomplete factorial design?
