Re: msg from atul

From: LSheiner <lewis@c255.ucsf.edu> Subject: Re: msg from atul Date: Tue, 14 Nov 2000 14:11:38 -0800 All - Picking up on the importance of "interaction", I recently had occasion to reconsider this, and came up with the following idea for the case that FOCE with interaction appeared to be indicated but was prohibitively time-consuming. What about taking a GLS-type approach? For concreteness, asume $ERROR fragment is: $ERROR IPRED = F Y = F + F*EPS(1) + EPS(2) Then: 1. Fit using FO with POSTHOC, and table IPRED (these will be good predictions, even if there is some bias in pop'n model, especially if data are fairly dense per individual, as data often are in precisely those cases that tend to give us biased estimates without INTERACTION ...) 2. Fit again, using previously tabled IPRED as an input data item called W, and use $ERROR IPRED = F Y = F + W*EPS(1) + EPS(2) One could, of course, cycle through this again an step 3, inputting the IPRED from step 2 as a new W ... Any thoughts? LBS. -- _/ _/ _/_/ _/_/_/ _/_/_/ Lewis B Sheiner, MD (lewis@c255.ucsf.edu) _/ _/ _/ _/_ _/_/ Professor: Lab. Med., Bioph. Sci., Med. _/ _/ _/ _/ _/ Box 0626, UCSF, SF, CA, 94143-0626 _/_/ _/_/ _/_/_/ _/ 415-476-1965 (v), 415-476-2796 (fax)