Traditional statistics are used in trying to find differences between two products. In the medical field, equivalence has become a goal. For example, a test product is very expensive and another product is inexpensive. The goal is to discover if they are equivalent so the cheaper one can be sold. In these tests, one is trying to determine if the two products are the same within a given tolerance level. Out of pure error, you will find that one product has an advantage over the other, when there is not any difference.
Four components must be addressed in evaluating a product, for example, a pre-operative skin preparation: