The user guide for scm seems to indicate that for the functionality of =
time-varying covariates, you need to estimate the standard deviation of =
the residual error as THETAS(s) (with SIGMAS(s) fixed to 1):
(see option “time_varying")
One more thing, before you switch to estimating the magnitude of the =
residual error as a fixed effect: notice that W should represent the =
standard deviation of the residual error (IRES in my example code =
below), and SIGMA(1,1) would generally represent the variance.
Below, I provide the code that I would use for the additive error with =
(the code with SIGMA fixed is provided in the scm user guide, under =
For other users, it should be noted that for covariates that are mostly =
varying between individuals, and just slightly over time (e.g. WT in =
adults), the option -time_varying in scm will have little or no impact.
But in this case, if another covariates is mostly varying over time, one =
may as well include WT among the ones listed as time varying (assuming =
WT was measured multiple times).
Example code for estimating additive error model with sigma estimated.
IPRED = [Model specific equation, or F]
IRES = DV-IPRED
ADD = SQRT(SIGMA(1,1))
SD = ADD
IWRES = IRES/SD
Y = IPRED + EPS(1)
Jakob Ribbing, Ph.D.
Senior Consultant, Pharmetheus AB
Cell/Mobile: +46 (0)70 514 33 77
Phone, Office: +46 (0)18 513 328
Uppsala Science Park, Dag Hammarskjölds väg 52B
SE-752 37 Uppsala, Sweden
This communication is confidential and is only intended for the use of =
the individual or entity to which it is directed. It may contain =
information that is privileged and exempt from disclosure under =
applicable law. If you are not the intended recipient please notify us =
immediately. Please do not copy it or disclose its contents to any other =
On 05 Oct 2017, at 15:38, Bernard Ngara <bernardngara4_at_gmail.com> wrote:
> Dear users
> I was trying to fit a covariate model using SCM approach in PsN with =
> model = run1.mod
> search_direction = both
> time_varying =CD4,HWT,BMI,AGE,TOAR,VAS
> continuous = 1,2
> categorical = 1,2
> The run fails and gives the following error message:
> Starting scm forward search
> Could not find assignment to W in $PRED needed for time_varying at =
C:/Portable_PKPD/Perl/bin/..\site\lib\PsN_4_7_0/tool/scm.pm line 5764.
> However I do have the W in the model file as:
> IF(DVID.EQ.1) W=SIGMA(2,2) ;
> IF(DVID.EQ.2) W=SIGMA(4,4)
> The baseline model runs well with stability and reasonable estimates =
of parameters but I am facing a challange on implementing the SCM.
> Kind regards
> Bernard Ngara
> +263 776 971 400
Received on Thu Oct 05 2017 - 10:40:13 EDT