Additionally, the natural choice to treat the prediction of potency (measured using the percent label claim of the product, %LC) and Total Degradation (TD) as numeric values forces the creation of regression models. However, the buffer type used as well as the presence of histidine were treated as factors. The first choice is required as the use of a phosphate buffer versus a tris buffer cannot be modeled numerically. The second choice is also required as only concentration of histidine was used in the DoE experiment.