RE: question in Box-Cox Transformations in K-PD model

From: Ribbing, Jakob Sent: 12 August 2013 23:45 To: 'kehua wu'; nmusers Cc: Ribbing, Jakob Subject: RE: [NMusers] Fwd: question in Box-Cox Transformations in K-PD model Hi Kehua, When you say that you did not get the estimate of TH2 in the output file, but you got the initial estimate. Did you mean that the model failed termination or that it minimised, but that TH2 did not move from its final estimate? I think we need more information from the control stream. Also, the part of the control stream that you shared did not include initial estimates. Did you start with a negative initial estimate for TH2? I would add an upper boundary at zero as well. For alternative statistical models with FOCE (or FOCEI, where appropriate) I have seen a couple cases were likelihood profiling indicates that there is information on the parameter, but where the estimate did not move from its initial estimate (to describe shape of individual parameter distribution or residual-error distribution) - These models were often complex or at least over parameterized in some regards - In your case; do you have enough information to estimate etas on KIN, KDE, EKD50 and EMAX, or are some of these omegas fixed? In addition, estimating EKD50 (theta and omega) often is very helpful to avoid correlation between the estimates (which is why this parameterisation was suggested in the first place). However, there are also cases where this parameterisation induces a correlation between the estimates and in that case estimating EA50 may be more useful. For the limited number of cases where I have tested different "semi-parametric" distributions for individual parameters; Box-cox transformation I have found to be one of the more stable alternatives. Best regards Jakob