Are Constraints Possible in a DSD?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.
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- 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!
Re: Are Constraints Possible in a DSD?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
Re: Are Constraints Possible in a DSD?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.
Re: Are Constraints Possible in a DSD?@DonMcCormack is correct about how DSDs started. Use the Alias-optimal criterion in Custom Design.
Re: Are Constraints Possible in a DSD?Yes, the red triangle menu options are in a text inset used across the DOE books, so it uses the "not available for some designs" to indicate that some options are not going to work for all designs. The text inset is intended to make sure that menu descriptions are consistent and stay updated across the books. I have opened a doc jira to look to look at the constraint options as it may make more sense to use 2 versions of the text insert such that constraints are not mentioned in chapters where they are not options.
