In your biological experiments, there will be situations where you have multiple options of compounds to use, all belonging to the same type. For each run in your experimental design, you need to select only one of these options. This can be considered as a categorical factor. However, it's often not enough to simply choose a category - you also want to examine the concentration of that chosen option (Figure 1).
Figure 1. Mutual exclusion factors are a combination of a categorical choice of liquid, which then is sampled numerically. For any run in the DOE design only one of the categorical choices will be sampled from the defined concentration range for that choice.
In assay development, you often encounter situations where you have to choose between different surfactants, such as Triton X-100, CHAPS, or Tween 20. However, it's not just the choice of surfactant that you want to test, but also the impact of varying concentrations when selecting each surfactant. This is a common occurrence in culture media optimization as well. For instance, you may have to choose between different carbon sources, like glucose, glycerol, or galactose, and simultaneously examine the effect of their concentrations on your system. This latter aspect can be considered as a numerical factor, and you are correct in thinking so.
But what happens if the different compound choices have different concentration units, or have very different active concentration ranges?
In most statistical software you would need to define multiple separate factors, one for the categorical choice component and another factor for each of the different concentration units or ranges. This means you can end up with many additional factors to define, as well as needing to then map the categorical choice levels to the correct concentration factor specific to that choice. Synthace takes care of this for you by allowing you to define a single mutual exclusion factor that includes the categorical choice along with the various concentration ranges and units.
To learn about the statistics behind mutually exclusive factors, click here.
To learn how to define a mutually exclusive factor in Synthace, click here.