RE: [Fwd: occasions during pregnancy]
Paul,
You might try plotting your etas 6-9 vs. trimester (coded at four levels) to
ensure that the IOV is truly random by occasion, as your model assumes.
Obviously, it is not unheard of that the IOV should be much larger than IIV,
but I wouldn't start with that assumption. Usually there is at least some
correlation within an individual. Good luck.
Kevin
Kevin Dykstra, PhD, FCP
+1 978.655.1943 (O)
+1 978.289.2987 (M)
[email protected] | http://qPharmetra.com
Quoted reply history
-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of [email protected]
Sent: Tuesday, March 01, 2011 10:53 AM
To: nm nm
Subject: [NMusers] [Fwd: occasions during pregnancy]
---------------------------- Original Message ----------------------------
Subject: occasions during pregnancy
From: [email protected]
Date: Tue, March 1, 2011 10:49 am
To: "nm nm" <[email protected]>
--------------------------------------------------------------------------
Hi all nmusers,
I thank all who responded my questions yesterday. Almost all the responses
suggested that several occasions of one patient should be put under one ID
#. I re-code my control stream and adjusted the data file as following:
$PK
K12 = THETA(1)*EXP(ETA(1))
CL=
THETA(2)*EXP(ETA(2)+ETA(6)*TRI1+ETA(7)*TRI2+ETA(8)*TRI3+ETA(9)*TRI4)
$OMEGA
.8;
.1 .8;
.1 .1 .8;
.1 .1 .1 .8;
.1 .1 .1 .1 .8;
$OMEGA BLOCK(1) 0.9;
$OMEGA BLOCK(1) SAME;
$OMEGA BLOCK(1) SAME;
$OMEGA BLOCK(1) SAME;
where TRI1,TRI2,TRI3, and TRI4 are different stages of pregnancy.
This model fits poorly for the data (from the plot of PRED, IPRED VS. DV),
although the estimates are stable and reasonable.
If I treat the different occasions as different patients, ignoring the
correlation within the same patients, then the model fits quite well and the
results are reasonable.
I also noticed one note from Lewis Sheiner:
Note that, as happens more often, at least with human data, than one might
have thought, the IOV>IIV, then treating each occaasion as though it were a
distinct individual is a reasonable approximation.
--------------Date: Wed, 17 Nov 1999 13:57:18 -0800
From: Lewis Sheiner <[email protected]>
Subject: Re: repeating cases---------
The parameters during pregnancy change quite large, so I am not sure if it
is a reasonalble approximation to treat occasions as distinct individual, or
I have to search the better models of putting those occasions under one ID?
and what is the direction to improve the model?
Any suggestion is greatly appreciated.
Paul
School of Pharmacy
University of Pittsburgh
716 Salk Hall
3501 Terrace Street
Pittsburgh, PA 15261
Phone: 412-648-8546
E-mail: [email protected]
Yuanyue (Paul) Gao
School of Pharmacy
University of Pittsburgh
716 Salk Hall
3501 Terrace Street
Pittsburgh, PA 15261
Phone: 412-648-8546
E-mail: [email protected]