RE: Questions about identifiability

Hi Silke A couple of quick comments. > The questions we have are: > 1. Are these experiments sufficient to conclude on the > model identifiability? Yes and no. Technically speaking what you have done is not sufficient to show identifiability of your model. You can either do a formal identifiability analysis or alternatively compute the expected Fisher information matrix for the parameters given your design. In the latter case if the information matrix is rank deficient or the determinant of the matrix is close to zero then you have some level of identifiability problem. The latter method cannot distinguish between structural identifiability (i.e. that the model has 2 or more parameters that cannot be locally identified irrespective of your design) from deterministic identifiability (i.e. your model is structurally identifiable but your design is insufficient to allow all of your parameters to be precisely estimated). The Fisher information matrix can be computed for any design using a variety of "optimal" design programs include WinPOPT (www.winpopt.com). It should be noted that being able to simulate and estimate model parameters under a particular design does not mean the model is structurally identifiable. I have seen several cases where precise parameter estimates occurred under a structurally non-identifiable model. However, I think it does provide reasonable evidence that all is well :-) Whether it is sufficient evidence depends on what you are developing the model for... I'll leave the other questions for the time being. Steve -- Professor Stephen Duffull Chair of Clinical Pharmacy School of Pharmacy University of Otago PO Box 913 Dunedin New Zealand E: [EMAIL PROTECTED] P: +64 3 479 5044 F: +64 3 479 7034 Design software: www.winpopt.com