topic Re: Mixture sum in Discussions

Mixture sum

Mytom — Thu, 08 Jun 2023 16:36:30 GMT

Hi.

I tried to make a custom designed mixture experiment with only two different ingredients with varying procents, all other ingredients is helt constant. I tried to use the "mixture sum" option to sum up the two ingredient at the maximum range but it does not work. The last ingredient gets changed into the value stated in mixture sum but that is not what I am after. Any suggestions on what could work?

Example:

Ingredient A have ranges 0.5 to 30%, B has 0.5 to 13%, Mixture sum is therefore 43%, but non of the ingredients should alone have up to 43%.

Re: Mixture sum

Dan_Obermiller — Mon, 13 Feb 2023 13:20:53 GMT

I think more details are needed.

From what you stated you are only wanting to change two components, A and B. A and B should add up to 43%. However, the only way for you to achieve that is if A is at its maximum and B is at its maximum. So there is only one trial: A=30% and B=13%. If you want less of component A, B MUST go higher than 13%.

Finally, note that with only two components changing, you really could just make a non-mixture design with just one of the components. The other just varies to reach the total.

Re: Mixture sum

Victor_G — Mon, 13 Feb 2023 13:37:10 GMT

Hi @Mytom,

As stated by @Dan_Obermiller, we are missing some informations to help you further and there might be a problem in your constraints.
Please note that if the total of your 2 ingredients is fixed in your formulation, you can also use one numeric factor in your design that will correspond to the ratio of your 2 ingredients (A/B), and specify high and low levels.

I hope this answer will help you,