RE: covariate selection question

From: mark.e.sale@gsk.com Subject: RE: [NMusers] covariate selection question Date: Wed, 18 Jan 2006 08:17:39 -0500 Mats, It isn't the step wise part of the traditional model building that is subjective. Step wise can be completely objective - as in the automated step wise linear and logistic regression algorithms in many stats packages. The subjective part comes when someone is weighing a 3 point decrease in OBJ, with maybe a little better time vs wres (or cwres), but not a compelling biological basis, but now fails a covariance step (which Nick tell us isn't really important anyway - and I'm beginning to agree ....) If all these were specified (and quantifiable?) prior to the analysis, then it would be fine, but they tend to be done real time during the analysis. So .... did the analyst at GSK (I mean Pfizer) decide that the race effect on K21 shouldn't be included because the plot really wasn't any better and it doesn't make any biological sense, or because it might cause problems in discussions about labelling? WRT your comment I think we all agree that improved model building procedures are valuable, but maybe the part that least needs new methods is the covariate model, we need much more guidance on how to build good structural models. I agree, I suspect that the best opportunity for improvement in most models is in the structural model, not the covariate model. Mark Sale M.D. Global Director, Research Modeling and Simulation GlaxoSmithKline 919-483-1808 Mobile 919-522-6668