From: tgordi@buffalo.edu Subject:NMusers] Error model Date:Thu, 10 Apr 2003 21:10:32 -0400 Dear all, I am trying to write an error model for a system, where 2 different measurements were made. One of these is log-transformed while the other is not. I would like to test an additive model for the log- transformed data and a proportiona error model for the other measurement. The two measurements are marked by a value of 1 or 0 in a separate column called PKone, where 1 means the first measurement and 0 means the second. I have tried to combine the two models in a couple of different ways but have not been successful. Any suggestions or references that I can look up? Toufigh Gordi _______________________________________________________ From: Nick HolfordSubject:Re: [NMusers] Error model Date:Fri, 11 Apr 2003 13:28:36 +1200 Toufigh, Its very hard to offer advice when you give no clue to the kind of problem you are having. I would start with something like this: $ERROR ;assumes log transformed prediction is Y1 and none transformed is Y2 IF (PKONE.EQ.1) THEN ; log transformed DV Y=LOG(Y1) + ERR(1) ENDIF IF (PKONE.EQ.0) THEN ; none transformed DV Y=Y2*(1+ERR(1)) ENDIF Nick _______________________________________________________ From: Leonid Gibiansky Subject:Re: [NMusers] Error model Date:Fri, 11 Apr 2003 10:51:15 -0400 I think there should be two different ERR(): IF (PKONE.EQ.1) THEN ; log transformed DV Y=LOG(Y1) + ERR(1) ENDIF IF (PKONE.EQ.0) THEN ; none transformed DV Y=Y2*(1+ERR(2)) ENDIF Leonid _______________________________________________________ From:Nick Holford Subject: Re: [NMusers] Error model Date:Sat, 12 Apr 2003 08:11:22 +1200 Leonid, Thanks for pointing out my typographic error. I did not intend to use the same ERR() for both models. I agree they should certainly be different. Nick _______________________________________________________