[size=4]I have some IV and oral PK data available from multiple subjects, and I would like to fit those data without using the population modeling feature in Phoenix. So the software fitted the IV data separately for each subject and gave me parameter estimates for each ID. Now I would like to do a simultaneous fitting of IV and oral data using the same approach. However, my question is how would I fix some parameter estimates for each ID separately when fitting the data simultaneously? Another question along the same lines is how would I specify parameters for each ID for simulation purposes? I tried to click through Setup → Parameter Setup → Use internal worksheets. All the parameters could then be entered for each ID separately. However, when I tried the run the simulation, Pheonix gives me an some error of “reference object not set to an instance of object…”. How can I do this in Pheonix? Thank you![/size]