RE: Describing variability

From: "Bachman, William" Subject:RE: [NMusers] Describing variability Date:Tue, 1 Apr 2003 08:59:27 -0500 As Diane suggests, you can get an acceptable fit without getting the $COV step to run successfully. $COV is a bonus if you can get it in some cases (e.g. with data that could have been better than what you've got to work with). I don't think Nick meant to imply that he would use a run with rounding errors regardless of the number of significant digits (e.g. significant digits not reported) and Leonid's criteria of 3 digits may be too strict. In some cases 2 digits is adequate. It's a judgement call. I also think dismissal of FO as quick and dirty is also a little over the top. It actually does a remarkably good job for sparse data in cases where you can't even get FOCE to converge. At the risk of sounding like a company stooge, we need to keep in mind what a daunting problem the nonlinear mixed effect modeling of clinical trial data is! That being said, there of course is room for improvement. The reason I even bring it up is that I get the impression that some people may be writing these opinions down as "RULES WRITTEN IN STONE". The judgement calls and opinions are what make modeling interesting for me. When it becomes all clearly defined or rule-driven, I'll go do something else! Bill