I-optimal custom DOE RSM design with continuous and categorical factors - centre points not balanced?

Here4DOE

Hi, I want to create an I-optimal custom DOE with 5 continuous factors and one categorical factor (with 2 levels). I also want to have 4 centre points which I specify on set-up. I also choose RSM for my model as I know there is curvature. When JMP creates the design, the centre points are not equally divided across the two categorical levels - one category gets 4 centre points and the other gets 2 centre points. I would manually alter them to be balanced, however, this would result in L1 having two more runs throughout the experiment than L2. Is there anything that I can do to ensure the centre points are balanced across these two levels?

DOE Set-UpDOE Table

Victor_G

Hi @Here4DOE,

 

The "quick fix" solution could be to create the design without the centre points (so that levels of the categorical factors are balanced), and manually add the 6 centre points (3 for L1, 3 for L2). You could then randomize your design table by using the Create a Subset Data Table platform with sampling rate of 1, to keep all rows from your design but randomize the order.

Note that if you really need to enforce a balance between your 2 levels of categorical factor, you need to have an even number of total runs (like 32 or 34 in your example). Else JMP will try to find the best trade-off/balance between the repartition of centre points and the "other" points so that all runs are distributed in a "balanced" way across all levels.

Hope this answer can help you,