Basic information for Central Composite designs
Central composite designs can have three (alpha=1) or five levels in all factors
and are useful for fitting second order polynomials to experimental data
based on several quantitative response variables.
They can be used in a process of sequential experimentation, experimenting first with the
cube portion and later adding (a) star block(s).
For more information, look at the help file for function
ccd.design from package DoE.wrapper
or at ccd from package rsm.
must be a valid name. The design itself is created under this name in the R workspace.
An existing 2-level fractional factorial,
preferrably of at least resolution V, can be selected, or a new design
for the cube portion can be generated;
if the number of center points is to be different between cube and star
portion of the design, the cube portion must be generated with center points.
The number of center points in the cube portion is ideally defined within the cube itself.
In that case, the number given refers to the center points in the star portion.
If the cube portion has no center points, a single number of center points is applied
to both the cube and the star portion.
Alternatively, a separate number can be
given to specify different numbers of center points for cube and star portion,
e.g. 0, 5 for the unfortunate situation where the cube portion has already
been run without any center points (not recommended!).)
determines how far inside (alpha<1) or outside (alpha>1) of the cube
the star points are positioned. The special values orthogonal (default)
or rotatable define calculated alpha values with interesting statistical properties.
However, it must of course be checked whether these make practical sense. For example,
if the orthogonal alpha turns out to be 2 but experimentation beyond 1.5 does not make sense,
the number should be defined manually.
can be provided for reproducing an existing design.
can be switched off in exceptional situations. Usually, one would not want to do that. Note that the checkbox here refers to the star portion only. For the cube portion, there is also such a checkbox.
Ulrike Groemping
~put references to the literature/web site here ~
See also FrF2 for the function defining the cube portion
of the design ccd.augment for the function that augments
the cube portion with the star points, also function ccd from package
rsm for the function that underlies function ccd.augment.