On testing structural identifiability by a simple scaling method: Relying on scaling symmetries can be misleading

8 pages.-- This is an open access article distributed under the terms of the Creative Commons Attribution LicenseA recent paper published in PLOS Computational Biology [1] introduces the Scaling Invariance Method (SIM) for analysing structural local identifiability and observability. These two properties define mathematically the possibility of determining the values of the parameters (identifiability) and states (observability) of a dynamic model by observing its output. In this note we warn that SIM considers scaling symmetries as the only possible cause of non-identifiability and non-observability. We show that other types of symmetries can cause the same problems without being detected by SIM, and that in those cases the method may lead one to conclude that the model is identifiable and observable when it is actually notAFV has received funding from a Ramón y Cajal Fellowship (RYC-2019-027537-I) and from the Spanish Ministry of Science, Innovation and Universities and the European Union FEDER under project grant SYNBIOCONTROL (DPI2017-82896-C2-2-R). GM was funded by the CSIC intramural project grant MOEBIUS (PIE 202070E062)Peer reviewe