RE: POSTHOC and ETA values disagree
From: "Eleveld, DJ" d.j.eleveld@anest.umcg.nl
Subject: RE: [NMusers] POSTHOC and ETA values disagree
Date: Fri, July 1, 2005 6:00 am
Hi Leonid,
You are right that I am mixing terminology, I will try to be more careful.
I agree with you that if one considers the POSTHOC values then one would come
to the conclusion that random effect ETA(4) may not be needed. I have done
this in my further analysis. I havent gotten FOCE analysis to work yet as
it is producing floating-point errors or numerical difficulties during
integration. I still am trying to some more limited parameter ranges.
However, if I had not chosen to perform POSTHOC analysis and only looked at
the estimated ETA(4) value I would come to a very different conclusion, i.e.
that random effect ETA(4) is necessary based on the ETA(4) estimation of 0.48.
So in this case the conclusions based on inspection of the ETA values or on
the POSTHOC values are very different.
Ultimately, I agree with your conclusion but I am confused as to how that
conclusion was reached. If the POSTHOC values disagree with the estimated
ETA values, which one is then "right"? It seems that you (as I do) consider
the POSTHOC results as more "important" than the estimated ETA results. If
this is in general a good idea then what are the estimated ETA values actually
good for?
From what I could gather from reading the NONMEM documentation I didnt see any
strong advice to examine the POSTHOC values to determine the necessity of using
specific random effects, only inspection of the estimated ETA values. I got the
impression that POSTHOC values are simply an interesting 'extra'. So basing
conclusions on the 'extra' POSTHOC information seems strange because I then have
to ignore the 'essential' ETA information. I think this is the basis of my
confusion here.
Unfortunately I cannot sensibly also remove random effect ETA(5) also as
this would lead to all individuals exhbiting the same degree of potentiation.
Visual inspection of the observations shows that this is not the case.
Doug