Re: Nested random effects with NONMEM?

From: LSheiner <lewis@c255.ucsf.edu> Subject: Re: Nested random effects with NONMEM? Date: Mon, 13 Mar 2000 10:43:04 -0800 At present, it is oriented to just 2 levels - within individual noise and between individual variation. With some difficulty it can he "fooled" into modeling a third intermediate level, usually inter-occasion variation. In your case, you would want litter-to-litter variation, rat-to-rat, and within-rat. It could be done if the max. number of rats within litter (n1) were small and the number of parameters in the within-rat model (n2) were also small, as the way one fools NONMEM into creating the middle layer is to use a different random effect for each parameter on each "occasion", or in your case, rat-within-litter. This uses a total of n2(n1+1) random effects. This total is limited to no greater than 30 in most current installations of NONMEM (note that because of the nested structure, this implies far fewer distinct random effect parameters, however). 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)