While I am aware of the QRPEM limitation in the earlier versions of NLME as far as nonlinear and time-varying (occasion) covariates, I am attempting to code a proportional effect of a lag time in a model using the following code (excerpt from my project):
TVLAG=tvtlag*(1 + (1-FAST)*theta_lag)
stparm( tlag= TVLAG*exp(ntlag) )
However, there is nothing nonlinear, nor time dependent about this covariate in the data set as the data set is only from the first dose. Thanks in advance!