Dear Jun:
Sorry for making you in the reading trouble:
Here is my question:
Is there any special specification on the employ of covariance:
The papers which I have read most always take the covariance excluded,such as
W21,w31 w32.If the Decrease of OFV between the model of the covriance included
and the one not is significantly meaningful,what choice should I do? I really
do not understand the correlation of Cl and V,if the convariance between the
two parameters does exist.Dose it truly exist in physiologically or just
mathematically?
Dear Hongpo,
I am not sure I understand your question. Can you rephrase?
Jun Shen
Millipore Corporation
2009/12/13 yhb5442387 <[email protected]>
Dear professor:
THE off diagnoal:
Sometimes we make the OMEGA syntax as follows:$omega 0.1 0.1,but $omega blokc
(2) 0.1 0.01 0.1 at another occasion.As we know,the only difference is whether
the off diagonal estimate be used.So is there any specila condition about the
existence of the W21,or some another W square like that?
Thank you !!!
--
工作和生活,都要开心的过.
你好,叶红波在此送上真挚的祝福.祝你开心,
叶红波
Deat Jun,the covariance?
Dear Hongpo
Covariance between CL and V etas can be or should be observed for the oral
route. CL and V are apparent parameters that are related by the unknown
bioavailability : these are CL/F and V/F, so there is a
physiological/pharmacological basis for the correlation.
Saik
----- Original Message -----
Quoted reply history
From: yhb5442387
To: nmusers
Sent: Monday, December 14, 2009 4:10 PM
Subject: [NMusers] Deat Jun,the covariance?
Dear Jun:
Sorry for making you in the reading trouble:
Here is my question:
Is there any special specification on the employ of covariance:
The papers which I have read most always take the covariance excluded,such as
W21,w31 w32.If the Decrease of OFV between the model of the covriance included
and the one not is significantly meaningful,what choice should I do? I really
do not understand the correlation of Cl and V,if the convariance between the
two parameters does exist.Dose it truly exist in physiologically or just
mathematically?
Dear Hongpo,
I am not sure I understand your question. Can you rephrase?
Jun Shen
Millipore Corporation
2009/12/13 yhb5442387 <[email protected]>
Dear professor:
THE off diagnoal:
Sometimes we make the OMEGA syntax as follows:$omega 0.1 0.1,but $omega
blokc (2) 0.1 0.01 0.1 at another occasion.As we know,the only difference is
whether the off diagonal estimate be used.So is there any specila condition
about the existence of the W21,or some another W square like that?
Thank you !!!
--
工作和生活,都要开心的过.
你好,叶红波在此送上真挚的祝福.祝你开心,
叶红波
Hello,
NONMEM has the following property related to intra-subject variability:
"During estimation by the first-order method, the exponential model and proportional models give identical results, i.e., NONMEM cannot distinguish between them." So, NONMEM transforms F*DEXP(ERR(1)) into F + F*ERR(1).
Is there an easy around it? I try to code the logit transformation. I cannot log-transform the original data as it is suggested in some publications including the presentation by Plan and Karlsson (Uppsala) because many values will be equal to plus or minus infinity. Will NONMEM "linearize" the following code:
Z = DLOG((F+THETA(10))/(1-F+THETA(10)))
Y = DEXP(Z + ERR(1))/(1 + DEXP(Z + ERR(1)))
Thanks!
Pavel
Dear Hongpo,
In my opinion, we develop a model specific for a data set. If your data set
supported estimation of such a covariance then I think you should include it
(as indicated by a statistical significant drop of OFV). It is better if you
could find some physiological meaning for those off diagonal covariances (as
mentioned by Saik). But it is not a reason enough to exclude a covariance
just because you couldn't find a physiological relevance. On the other hand,
even if you have a strong belief that a covariance exists, if your data set
doesn't support, I really doubt inclusion of such an unidentifiable
covarinace would do any good unless you have good prior knowledge (then you
can try to fix it).
Welcome more comments.
Jun
Millipore Corporation
Quoted reply history
2009/12/14 yhb5442387 <[email protected]>
>
> Dear Jun:
> Sorry for making you in the reading trouble:
> Here is my question:
> Is there any special specification on the employ of covariance:
> The papers which I have read most always take the covariance excluded,such
> as W21,w31 w32.If the Decrease of OFV between the model of the covriance
> included and the one not is significantly meaningful,what choice should I
> do? I really do not understand the correlation of Cl and V,if the
> convariance between the two parameters does exist.Dose it truly exist
> in physiologically or just mathematically?
>
>
> Dear Hongpo,
>
> I am not sure I understand your question. Can you rephrase?
>
> Jun Shen
> Millipore Corporation
>
> 2009/12/13 yhb5442387 <[email protected]>
>
>>
>> Dear professor:
>>
>> THE off diagnoal:
>>
>> Sometimes we make the OMEGA syntax as follows:$omega 0.1 0.1,but $omega
>> blokc (2) 0.1 0.01 0.1 at another occasion.As we know,the only difference is
>> whether the off diagonal estimate be used.So is there any specila condition
>> about the existence of the W21,or some another W square like that?
>>
>> Thank you !!!
>>
>
> --
> 工作和生活,都要开心的过.
> 你好,叶红波在此送上真挚的祝福.祝你开心,
> 叶红波
>
>
>
Hello,
NONMEM has the following property related to intra-subject variability:
"During estimation by the first-order method, the exponential model and
proportional models give identical results, i.e., NONMEM cannot distinguish
between them." So, NONMEM transforms F*DEXP(ERR(1)) into F + F*ERR(1).
Is there an easy around it? I try to code the logit transformation. I cannot
log-transform the original data as it is suggested in some publications
including the presentation by Plan and Karlsson (Uppsala) because many values
will be equal to plus or minus infinity. Will NONMEM "linearize" the following
code:
Z = DLOG((F+THETA(10))/(1-F+THETA(10)))
Y = DEXP(Z + ERR(1))/(1 + DEXP(Z + ERR(1)))
Thanks!
Pavel