No argument about that. What concerns me here is the idea of using something other than the REAL result for a below LOQ value, especially when its weight can now be determined easily and in a cost effective way. Read the paper. Then let's talk more. It seems to me that the real use one wishes to make of these is to develop the very best dosage regimen possible based on the raw data of the previous population of patients studied.
Exact achievement is what is assumed.
Yes, there ARE many other sources of error besides the assay error. However, many people assume that the assay error is just a small part of the overall errors produced by errors in preparation of each dose, in the administration of the various doses, and in the recording of the times when serum concentrations are measured. They use a lumped term for intraindividual variability. Then, we consider the other sources of error as a separate measure of intraindividual variability. This we call gamma, and we use it to scale the assay error polynomial.