JMP Mixture Design Parameter Coding

thaumaturgy

Basic question:  I have an EXTREME VERTEX design for 4 factors generated in JMP.  How are the parameters coded?  For instance I have a variable (CaCl2) that gets coded in the Parameter table as

(CaCl2-0.3)/0.36

Where do the values "0.3" and "0.36" come from?  The mean of the CaCl2 levels is not either number.  All the other parameters are coded with "/0.36" in all of them. 

Thanks

-Chris

Dan_Obermiller

This is called Lower Pseudocomponent coding. The formula is "Coded CaCl2" = (CaCl2 - the lower bound of CaCl2) / (1 - sum of all lower bounds).

So without the details of this design and your four factors, the lower bound for all of your component ranges add up to 0.64 since 1 - 0.64 = 0.36. The lower bound for CaCl2 is 0.3.

This pseudocomponent coding tries to "expand" the factor space to fill up as much of the design simplex as possible. This will reduce the collinearity of your factors as much as possible, so what JMP is doing is a good thing.

- Dan