Are Constraints Possible in a DSD?

Question

I am (or was) reasonably certain that factor constraints are not possible with Definitive Screening Designs, but the GUI and the JMP documentation are making me feel that they might be possible.

* The GUI has red triangle options for saving and loading factor constraints. These are greyed-out for me basically no matter what combinations of factors I try:*

* The DOE Guidebook and JMP Online Help both have language about saving and loading constraints. But, there is language that says "not available for some designs.* "

* Brad Jones says DSDs shouldn't be used with constraints.

So, is this just a case of JMP's GUI and Documentation taking shortcuts (disabling menu items rather than deleting them, and "not available for some designs" means "not available for DSDs"), or is there a way to use constraints in DSDs, even if it's a bad idea?

Thanks!

Phil_Kay · Accepted Answer

Hi @Jed_Campbell ,

Looks like that part of the documentation for DSDs is a bit of a copy and paste job.

Constraints don't make any sense for a DSD. You would not be able to generate a DSD if there is a constraint that means some corner of the factor space is not allowed.

For what it's worth, I present DSDs as a great way to get started with DOE. They work very well in many common situations and require few choices of the experimenter. For everything else, Custom Design. And I give the example of a constrained factor space as the most common situation where DSDs don't work.

Hope that helps,
Phil

DonMcCormack · Accepted Answer

Strictly speaking, no. DSDs are constructed using orthogonal matrices which only have ±1 and 0 as elements. That said, you can get a DSD-like constrained space by using the Custom Designer with constraints and setting the main effects and quadratics to Necessary and the 2 factor interactions to If Possible. You'll lose the some of the nice properties of DSDs, particularly the orthogonality between main effects/2FI and main effects/quadratics, but you'll be able to get the constraints in there. BTW, if my memory is correct, this is how Brad and Chris Natchsheim started looking for these designs.