I have a question regarding products with multiple testing variables. For example, a single product will be tested for pH, %solids and zeta potential. There are no rational population subgroups. Right now, I am calculating a Pp/Ppk among other metrics for all three tests separately. Is there any accepted methodology for looking at the product as a whole (e.g. averaging the Ppk from each test)? I assume not, and I know multivariate analysis is heavily debated as to its effectiveness. I guess I'm more interested in any practical approaches industry has taken in a similar position. Thank you for any input!