RE: Describing variability

From:Scott VanWart Subject:RE: [NMusers] Describing variability Date:Wed, 02 Apr 2003 11:55:44 -0500 To chip in my two cents, the list Leonid prepared was very nice, but of course we all realize that certain guidelines will not always apply to every situation that arises. It is always wise to think through all the diagnostics that are available when evaluating a model. As for the rounding errors problems, I agree with Bill that this does not always indicate that the model is flawed. It could be that your initial parameter estimates need to be refined to help the search process, or that NONMEM cannot determine a particular level of precision for a given parameter. I find it helpful to sometimes "tweak" the system by increasing the number of significant digits in $EST from the default (3) to a larger number such as 4. This often is enough to prevent the rounding error problems from occurring. If after following these suggestions the rounding error problems continue to persist, this could be an indication that the data is not sufficient to estimate that parameter or there may be some other problem with your model. Scott