Constraints experimental design affected

The mixture design is a class of experimentation that is different from the previous designs we have discussed, wherein the assumption is that all factor levels are independent. In the case of the mixture design, there is an assumed relationship among factors. Suppose that in a chemical mixing experiment of two chemicals, the experimenter would like to test how the quantity of each chemical affects the properties of mixed chemical. In this case, we use the previous design. However, if the experimenter would like to study the effect of chemical ratio of two substances such as 1 1 or 2 3, a mixture design is used under a constraint that summation of the ratio must be equal to 1 [57]. 

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