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Central Composite Design

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Definition

An experimental design that is used to model a quadratic response surface. It uses a combination of factorial runs, replicated center runs and axial runs to estimate factorial effects and to test for and estimate curvature in the design space.

There are three types of central composite designs (CCDs):

1. Circumscribed (CCC), used when the region of operability (the region in which the Factors can vary without breaking the process) is contained within the region of interest (the region about which we’re interested in drawing conclusions). These designs have five levels for each factor.

2. Inscribed (CCI), used when the region of operability coincides with the region of interest. These designs have five levels for each factor.

3. Face-centered (CCF), used when one or more categorical Factors are included in the study, requiring the axial points to fall on the faces of the design cube corresponding to the high and low levels of the categorical factor. These designs have three levels for each factor.

Application

This is a class of Response surface designs that can deal with curvature in the process space under study. These designs are formed as extensions to two-level Factorial Designs (full or fractional) with the addition of center points and axial points.

See Also

Box Behnken designs as an alternative to CCDs.
Circumscribed CCD
Inscribed CCD
Face Centered CCD

External Links

Overview of the types of CCDs: - http://www.itl.nist.gov/div898/handbook/pri/section3/pri3361.htm