Hi, While running a popPK model with NLME, I do sometimes get the variability being calculated for the theta, sometimes not. Any idea as to why this happens? Using PHX 1.2, NLME 1.1
Variability can mean different things: residual error between subject variability uncertainty ( standard error on estimate) I assume you meant the standard error of estimates. Most of the time it is because the hessian cannot be inverted ( overparameterization , local minimum, ) try to fix a parameter or change your initial estimate. Samer
Christoph, as Samer indicated, I sometimes find that ‘accepting all’ on the final estimates and then re-executing will give me the SE. Another thing to consider is the algorithm you have selected; the FOCE-ELS often gives better results for many problem types that the -LB variant. Simon