Placebo in indirect PD models

From: "INTV (Ivan Nestorov)" nestorvi@zgi.com Subject: [NMusers] Placebo in indirect PD models Date: Wed, 26 Apr 2006 16:36:39 -0700 Dear All, I would be interested if anybody from the list can share ideas and experiences with ways to include placebo in indirect PD models. Considering (one type of such) model - with inhibition of synthesys, I have seen this done by: DADT(n) = SYN*(ACTIVE+PLACEBO) - LOSS*A(n), where the term for placebo may range from nothing (leaving all the placebo observations at the mercy of the residual error), all the way to a complex periodic function, adding at least three more thetas to estimate and thus almost always overparametrizing your model. In addition to this, it is a pain, if at all possible, estimating IIV on both SYN, components of ACTIVE and of PLACEBO because of the interaction between them in the equation above. Kind Regards. Ivan Nestorov Zymogenetics 1201 Eastlake Avenue East Seattle, Washington 98102 Tel: 206 442 6613 Fax: 206 442 6608 Cell: 425 442 9303 Email: intv@zgi.com