DOE for a single component with different sources & levels

Question

I am trying to optimize the maltodextrin component of a formulation. There are 3 different maltodextrins I would like to assess (different suppliers - categorical), and I would like to run each at 3 concentrations/levels.

It doesn't make sense to put the 3 different maltodextrin options as different factors, because they will never be used together - the idea is to choose the best one. I could do 3 separate one-factor DOEs, but this seems inefficient.

Is there a good design to simultaneously assess which maltodextrin is the best and which concentration is the best?

Thanks!

statman · Answer

I won't argue with the CoA and how they sample the material to obtain this, but doesn't the CoA list an actual DE value? And isn't that value from a continuous measurement scale?
In this case, why not make the factors DE and Concentration.  It seems that both are actually continuous variables and it would be nice to know the best combination?  This could be modeled if you ran a 3^2 factorial.  Otherwise you could optimize concentration within each DE value and then compare those "best" conditions from each DE.

thaumi · Answer

@P_Bartell thank you for these points - definitely all important considerations.

In this case, I am trying to look at differences caused by a characteristic of the maltodextrin itself (the dextrose equivalents/DE). It's hugely important to a few different aspects of our process (and, as you mentioned below - there are many different outcomes to balance). I just said "different suppliers" as a shorthand to indicate categorical levels (because different suppliers do make the different DE products), but  think I learned a lesson in this post about trying to simplify things but making them more complicated as a result.

I appreciate the input!

thaumi · Answer

Hi @statman. Thanks for your quick & thoughtful response. Yes, I am just trying to pick a winner as opposed to determining causality.

1) I don't believe that within-supplier variability is actually a major concern in this case. This experiment will use highly purified chemicals that come with CoAs certifying lot dextrose equivalents (DE), which is the actual parameter we care about between suppliers. We know from past work there is very low variation surrounding these dextrose equivalents between different lots from the same supplier. But yes, I am also not sure if a DOE is the correct approach here, which is the reason for my question :)

2) We have well-established and robust measurement systems with low variability and have quantified and assessed these in the past - again, not a major concern for us in this case.

3) The maltodextrin itself is "pure" regardless of supplier, but as mentioned above, they will have different DE values. The plan is to dissolve different amounts of each type to different concentrations, and ultimately to assess both source & concentration on our final product.

4) Good question. Typically for a non-DOE experiment, we will process things in triplicate, and as long as our variation is low, leave it at this. Obviously with DOEs this is not always the case. But as mentioned above, I am not that concerned about a high level of within-source variability.

Thanks again for your time!