Similarity testing has been introduced with the chapters on biological assays in the US Pharmacopeia <1032>, <1033>, <1034> it is the approach to prove the validity of your bioassay. In similarity testing, you compare regression parameters, differences of parameters or ratios or parameters along with their confidence intervals to equivalence margins. If the confidence interval falls completely into the range of the equivalence margins, the test is passed.
The challenge of this type of testing is the development of suitable equivalence margins. The Equivalence Margin Development document type of PLA 3.0 allows you to calculate candidate equivalence margins from historic assay data.