RE: offsets

From: "Piotrovskij, Vladimir [JanBe]" <VPIOTROV@janbe.jnj.com> Subject: RE: offsets Date: Wed, 3 Mar 1999 09:44:44 +0100 Dear Joseph, I don't know what to you mean saying "works better". My experience is that fitting Eq[1] usually creates problems whereas Eq[2] does not. With Eq [1] you have to constrain properly initial estimates for THETAs to avoid CL<=0. Of course, the interpretation of THETA(1) in Eq [1] is more transparent: it is just a typical CL in individuals of 30 yr old. If 30 yr is the median age in your (sub)population, everything is fine. On the contrary, THETA(1) in Eq. [2] is an intercept which may even be negative and thus difficult to interpret. Hope this helps. Best regards, Vladimir ---------------------------------------------------- Vladimir Piotrovsky, PhD Clinical Pharmacokinetics, ext 5463 Janssen Research Foundation 2340 Beerse, Belgium e-mail: vpiotrov@janbe.jnj.com