RE: Error when combining proportional residual error,

From: "Serge Guzy" GUZY@xoma.com Subject: RE: [NMusers] Error when combining proportional residual error, Date: Wed, 2 Aug 2006 09:14:55 -0700 I think the problem is that you did not define really a combined proportional with additive but instead an exponential error + additive. Can you try to write instead IF (STDY.EQ.1) THEN Y=IPRD* (1+EPS(1)) +EPS(5) ENDIF IF (STDY.EQ.2) THEN Y=IPRD* (1+EPS(2)) +EPS(6) ENDIF IF (STDY.EQ.3) THEN Y=IPRD* (1+EPS(3)) +EPS(7) ENDIF IF (STDY.EQ.4) THEN Y=IPRD*(1+EPS(4)) +EPS(8) ENDIF In the MCPEM program for example, an exponential error variance does not really exist. When you assume exponential error variance, the data are log-transformed and the error model is then assumed to follow a constant variance model. In the MCPEM it does not make any sense to combine exponential with additive. I guess something similar is used with NONMEM. Serge Guzy President POP-PHARM