RE: Analysis of sparse data

From: "Piotrovskij, Vladimir [JanBe]" <VPIOTROV@janbe.jnj.com> Subject: RE: Analysis of sparse data Date: Mon, 2 Aug 1999 13:35:42 +0200 Dear Sriram, Your problem is quite typical. The two data sets you have, apparently, differ not only in the number of plasma samples per subject and in that they came from distinct populations. Most probably, your rich data set was obtained in a well-controlled Phase I study whereas the sparse data set was from a Phase II or III trial. Hence, the residual error could not be the same. So, when you merge the two data sets you should create an indicator variable to distinguish them and include two ERRs in $ERROR block. To avoid merging you can fix some of PK parameters, particularly, KA to the estimates obtained with the rich data set. As to the random effect parameters (ETAs) I would suggest using the full variance-covariance matrix (the BLOCK option in the $OMEGA block). Hope this helps, Vladimir ---------------------------------------------------------------------- Vladimir Piotrovsky, Ph.D. Janssen Research Foundation (5463) Clinical Pharmacokinetics B-2340 Beerse Belgium Email: vpiotrov@janbe.jnj.com