RE: PK models for rich and sparse sampling

From: mark.e.sale@gsk.com Subject: RE: [NMusers] PK models for rich and sparse sampling Date: Tue, 1 Jun 2004 06:46:34 -0400 My understanding is that NONMEM does use an inverse Wishart for OMEGA (and Normal for THETA). I've found that while there isn't any good way to determine the appropriate DF for OMEGA (or so I've been told by smart people), once you get beyond about 5 DF, the result isn't very sensitive to the choice (I usually use about 20). We have played a little with relating DF for inverse Wishart with SEE for OMEGA (using Monte Carlo simulation, to get DF for the sampling optimisation work), but not yet completely satisfactory. But, I think a little more work and this will be possible. Bottom line is that I don't think it matters (much), it you have at least 5 DF. Mark