RE: Is it reasonable to add covarite to PD parameters kin or kout?
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 observations
and thus have a lot of explanatory power; this is the reason they appear
significant more often than not. Comparisons after treatments should try to use
all information before treatments (thus including baselines).
Statisticians habitually use baselines as covariates in their ANCOVA models for
obviously good reasons.
Regards,
Peiming
Quoted reply history
From: [email protected] [mailto:[email protected]] On
Behalf Of Mark Sale
Sent: Tuesday, July 28, 2015 3:34 AM
To: Zhao,Li; [email protected]
Subject: [NMusers] RE: Is it reasonable to add covarite to PD parameters kin or
kout?
Li,
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 is 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 observed value to
predict the parameters (which then predict the observed value). Also note that
covariates are, by definition, measured without error, and a baseline value is
likely measure with error (the same error as any other observation?).
Mark
From: [email protected]<mailto:[email protected]>
[mailto:[email protected]] On Behalf Of Zhao,Li
Sent: Monday, July 27, 2015 2:39 PM
To: [email protected]<mailto:[email protected]>
Subject: [NMusers] Is it reasonable to add covarite to PD parameters kin or
kout?
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 significant 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!