converting epsilon to CV

From: alison@c255.ucsf.EDU (ABoeckmann) Subject: converting epsilon to CV Date: 17 Mar 1998 12:05:49 -0500 The message ERROR IN LOG Y IS MODELED comes from PREDPP. See Users Guide V (Introductory) Chapt 8, Section 3.2: During data analysis NONMEM cannot distinguish between the CCV error model Y = F + F*EPS and the exponential error model Y = F * EXP(EPS), for which LOG (Y) = LOG (F) +EPS. By using the latter model and modelling the error in LOG (Y) rather than in Y, NM-TRAN enables PREDPP to achieve an improvement in run time. Because the HH derivative (the derivative of log y with respect to epsilon) is a constant, it can be arranged that ERROR need only be called once, at the beginning of the problem, thus avoiding many subroutine calls. PREDPP itself forms the H derivative (the derivative of y with respect to epsilon). There is further discussion of this in chapter IV of Guide VI. The question about what CV to use was addressed by Dr. Beal in messages to this mailinglist last year. The orignal message, with some discussion, is attached for those who have not seen it, or who do not have access to the archive. -- Alison Boeckmann