NONMEM Users Network Archive

Hosted by Cognigen

RE: Is it reasonable to add covarite to PD parameters kin or kout?

From: Peiming Ma <>
Date: Tue, 28 Jul 2015 01:30:33 +0000

Dear Mark and Li,

I think there is nothing wrong with using baseline as a covariate. Baseline=
 observations contain more information than just some pre-treatment observa=
tions and thus have a lot of explanatory power; this is the reason they app=
ear significant more often than not. Comparisons after treatments should tr=
y to use all information before treatments (thus including baselines).

Statisticians habitually use baselines as covariates in their ANCOVA models=
 for obviously good reasons.


From: owner-nmusers
 Behalf Of Mark Sale
Sent: Tuesday, July 28, 2015 3:34 AM
To: Zhao,Li; nmusers
Subject: [NMusers] RE: Is it reasonable to add covarite to PD parameters ki=
n or kout?

I'm going to go out on a limb (since I haven't seen your data or understand=
 the biology) and suggest that the baseline value is not a covariate, but i=
s just another observation (presumably with drug concentration = 0). The=
 baseline value is sort of by definition a function of kin. So, you might =
look for predictors of Kin (age? Disease stage?) rather than using the obse=
rved value to predict the parameters (which then predict the observed value=
). Also note that covariates are, by definition, measured without error, a=
nd a baseline value is likely measure with error (the same error as any oth=
er observation?).


From: owner-nmusers
Sent: Monday, July 27, 2015 2:39 PM
To: nmusers
Subject: [NMusers] Is it reasonable to add covarite to PD parameters kin or=

Dear NMusers,

Right now I am doing covarite analysis for an indirect response model.

 I tested a few potential covarites and found it's STATISTICALLY significan=
t if I add observed baseline value to kin.

But I am not sure if it makes sense to add the baseline value as a covarite=
 to kin.

Could you please help me if you have had similar experiences before?

Thank you very much!

Received on Mon Jul 27 2015 - 21:30:33 EDT

The NONMEM Users Network is maintained by ICON plc. Requests to subscribe to the network should be sent to:

Once subscribed, you may contribute to the discussion by emailing: