RE: Residuals and INTERACTION for simultaneous PK/PD, impos sible?

From: "Piotrovskij, Vladimir [PRDBE]" VPIOTROV@PRDBE.jnj.com Subject: RE: [NMusers] Residuals and INTERACTION for simultaneous PK/PD, impos sible? Date: Fri, April 15, 2005 3:18 pm Doug, The only solution to your problem that I see is to make the residual error for the PK model also homoscedastic. You can easily do this by converting concentrations into logarithms and declaring log(C) as DV. Then you do the same for the model prediction F, e.g. $ERROR CALLFL=0 LOQ = 1 ; limit of quantification FLAG = 0 IF (F.LE.0) FLAG=1 IPRE = (1-FLAG)*LOG(F+FLAG) + FLAG*LOG(LOQ) ; returns log(LOQ) if F<=0 Y = IPRE + EPS(1) etc. BTW, log transformation of concentrations is a preferable approach when you do just PK modeling. Best regards, Vladimir ----------------------------------------------------------------- Vladimir Piotrovsky, Ph.D. Research Fellow, Advanced Modeling & Simulation Johnson & Johnson Pharmaceutical Research & Development Beerse Belgium