How select the best designDear all,
We would like to make experiments with 5 continuous factors. Our system is a chemical reaction. We know there are interactions between factors but we don’t know to which extend. We would like to maximize the amount of product.
There are a lot of possible DOE’s. I think about
-central composite design,
-OR first part of it (for main effects and central points) and then augment the design,
-OR DSD and then augment the design
-OR custom design with 2d order and quadratic interactions
-OR custom design and select RSM.
How can I select the best design for us? Which argument would help me to choose?
Thanks
DOERe: How select the best designI bet that all 5 factors are important and you already know that from prior knowledge of the chemical reaction. If so, then I would not start with a screening experiment because the key screening principles are likely not to hold. There is uncertainty about the factor effects, however, so you might use the Estimability attribute of model terms to specify that uncertainty.
It will probably come down to your budget of runs. So I would make a custom design for the 5 factors. (Are any factors hard to change?) I would click the RSM button in the Model section. It will enter terms in the model for all possible second-order interactions and non-linearities. (This action will also change the criterion to I-optimal.) Now inspect each term in the model. Ask yourself if you know that this term is necessary, you know it is not necessary, or you think it might be necessary. Remove any term that you know is not necessary. Leave all terms that you know are necessary alone. Change the estimability of the remaining terms to If Possible. This process will result in two changes. The minimum number of runs will fall - this number is equal to the number of parameters that must be estimated. Also, the design will be I-optimal for all possible models. Now increase the number of runs in the following way. Add 3-4 runs for every If Possible term that might be significant. Say that I have 10 terms for interactions that might be possible, I don't know which ones will be active, but I think that 2 of them will be active. Add 6-8 runs to the minimum.
Does this reasoning and approach make sense?
Re: How select the best designHello Statman, I think points 1 and 2 are ok. We made pre-tests regarding the measurement system, and we prepared the tests in a way to lower noise as much as possible. Thanks a lot for your other suggestions.
