Hello,

I am trying to design and then analyse a mixture design with non-mixture factors and am having some trouble understanding how to do it properly. Briefly I am running an experiment on a blend of components under different temperature conditions. The samples are a blend of component 1 with component 2, where component 2 is one of three related materials. What I am having trouble with is encoding the fact that when component 2 = 0 the material of component 2 obviously has no effect on the result as it is completely absent. Using the below factors for the design and restricting factors such that when component 2 = 0, component 2 is not allowed to be A or B for example produces a reasonable design matrix. However when trying to analyse I run into the problem that the model assumes that the type of component 2 (A, B, or C) has an effect on the response even when Component 2 = 0 (i.e is absent).

Component 1: 0-1 (continuous, mixture)

Component 2: 0-1 (continuous, mixture)

Component 2 Type: A, B, C (categorical)

Temperature: 40-150 (continuous)

Can anybody help me with a better way to either generate the design matrix or perform the analysis.

Thanks,

David Gillespie