RE: Your suggestions/thoughts needed on allometric base or final model

From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Hong-Guang Xie Sent: Friday, July 11, 2008 12:36 PM To: [email protected] Subject: [NMusers] Your suggestions/thoughts needed on allometric base or final model Dear NMusers: As you know, body weight is an important covariate that is integrated into the final or covariate model in some cases. When analyzing pediatric pop PK data, body weight-based allometric ¾ power model is used frequently. By definition, base model is a model without any covariates. But, in the literature on the population PK in pediatrics, I noted that body weight is added to the structural model (following the principles of allometry) before starting the covariate model building in some but not in all studies. That means that some models are called allometric base models and others are not. What are their differences? For the allometric base model, body weight has been added into the base model regardless of whether it is an important covariate (in some cases, body weight is not). If body weight is not an important covariate as determined by further covariate model building, is there still the need to add body weight into the final allometric model (if its corresponding base model is one without a body weight-associated allometric component)? Logically, such a need seems to be not reasonable. How to deal with this conflict? Is there an almost agreeable thought on this issue in our community? Thank you, Hong-Guang