Algorithm to Find New Identifiable Reparameterizations of Parameteric Rational ODE Models

Structural identifiability concerns the question of which unknown parameters of a model can be recovered from (perfect) input–output (IO) data. If all of the parameters of a model can be recovered from data, then the model is said to be identifiable. However, in many models, there are parameters that can take on an infinite number of values but yield the same input–output data. In this case, those parameters and the model are called unidentifiable. The question is then what to do with an unidentifiable model. One can try to add more input–output data or decrease the number of unknown parameters, if experimentally feasible, or try to find a reparameterization to make the model identifiable. In this article, we take the latter approach. While existing approaches to find identifiable reparameterizations were limited to scaling reparameterizations or were not guaranteed to find a globally identifiable reparameterization even if it exists, we significantly broaden the class of models for which we can find a globally identifiable model with the same input–output behavior as the original one. We also prove that, for linear models, a globally identifiable reparameterization always exists and shows that, for a certain class of linear compartmental models, with and without inputs, an explicit reparameterization formula exists. We illustrate our method on several examples and provide detailed analysis in the Supplementary Material on github.