Relative potency

The potency of a test sample expressed as a ratio to a reference standard measured in the same assay run. Biological assays vary from day to day, and comparing each sample with a standard on the same plate cancels much of that variation. The calculation usually fits dose-response curves, for example with a four-parameter logistic model, and requires the sample and standard curves to be parallel. Japanese specifications for biologics often state potency as a percentage of the reference standard within an acceptance range.