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From: Leander, Jacob <Jacob.Leander_at_astrazeneca.com>

Date: Wed, 13 Apr 2016 11:01:29 +0000

Hi

Consider the case where we have a categorical (potentially time-varying) co=

variate named CAT that can take several values (e.g. 0,1,2,3).

Let's say I want to model CL depending on this categorical covariate (where=

parameters are estimated on log-scale).

A simple solution to this would be

IF(CAT.EQ.1) TVCL = THETA(1)

IF(CAT.EQ.2) TVCL = THETA(2)

IF(CAT.EQ.3) TVCL = THETA(3)

I let CL be described by a log-normal distribution with the same omega elem=

ent for all CAT values.

CL = EXP(TVCL + ETA(1))

With an omega statement:

$OMEGA 0.1

I now want to switch to the mu referencing framework in NONMEM. Each theta =

needs to be reference to a MU value, and to force it to be described by the=

same eta I apply the following approach.

MU_1 = THETA(1)

MU_2 = THETA(2)

MU_3 = THETA(3)

IF(CAT.EQ.1) CL = EXP(MU_1 + ETA(1))

IF(CAT.EQ.2) CL = EXP(MU_2 + ETA(2))

IF(CAT.EQ.3) CL = EXP(MU_3 + ETA(3))

With an omega statement:

$OMEGA BLOCK(1) 0.1

$OMEGA BLOCK(1) SAME

$OMEGA BLOCK(1) SAME

where I force the omega element corresponding to ETA1, ETA2 and ETA3 to be=

the same.

Is this a valid approach to obtain what I need?

Or is there a simpler way in the mu-referencing framework to link different=

thetas to the same omega element?

All the best,

Jacob

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Received on Wed Apr 13 2016 - 07:01:29 EDT

Date: Wed, 13 Apr 2016 11:01:29 +0000

Hi

Consider the case where we have a categorical (potentially time-varying) co=

variate named CAT that can take several values (e.g. 0,1,2,3).

Let's say I want to model CL depending on this categorical covariate (where=

parameters are estimated on log-scale).

A simple solution to this would be

IF(CAT.EQ.1) TVCL = THETA(1)

IF(CAT.EQ.2) TVCL = THETA(2)

IF(CAT.EQ.3) TVCL = THETA(3)

I let CL be described by a log-normal distribution with the same omega elem=

ent for all CAT values.

CL = EXP(TVCL + ETA(1))

With an omega statement:

$OMEGA 0.1

I now want to switch to the mu referencing framework in NONMEM. Each theta =

needs to be reference to a MU value, and to force it to be described by the=

same eta I apply the following approach.

MU_1 = THETA(1)

MU_2 = THETA(2)

MU_3 = THETA(3)

IF(CAT.EQ.1) CL = EXP(MU_1 + ETA(1))

IF(CAT.EQ.2) CL = EXP(MU_2 + ETA(2))

IF(CAT.EQ.3) CL = EXP(MU_3 + ETA(3))

With an omega statement:

$OMEGA BLOCK(1) 0.1

$OMEGA BLOCK(1) SAME

$OMEGA BLOCK(1) SAME

where I force the omega element corresponding to ETA1, ETA2 and ETA3 to be=

the same.

Is this a valid approach to obtain what I need?

Or is there a simpler way in the mu-referencing framework to link different=

thetas to the same omega element?

All the best,

Jacob

________________________________

Confidentiality Notice: This message is private and may contain confidentia=

l and proprietary information. If you have received this message in error, =

please notify us and remove it from your system and note that you must not =

copy, distribute or take any action in reliance on it. Any unauthorized use=

or disclosure of the contents of this message is not permitted and may be =

unlawful.

Received on Wed Apr 13 2016 - 07:01:29 EDT