NONMEM Users Network Archive

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RE: algorithm limits

From: Mark Sale - Next Level Solutions <mark>
Date: Sat, 19 Jul 2008 14:51:05 -0700

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Received on Sat Jul 19 2008 - 17:51:05 EDT

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Leonid,
 This isn't PK, and the model show basically the right s= hape, and the data suggest reasonable residual error (the biological marker= falls from a value between 5 and 310000, to somewhere between 0 and no cha= nge from baseline, over a course of a couple of hours to a couple of weeks,= then recovers somewhere between a 100 hours and 9000 hours later.)
ie.,= it start at a highly variable level fall by some highly variable fraction,= over some variable lenghth of time and recovers somewhere between about a = week and about a year.
But, within those limits, it appears pretty well = behaved.


Mark Sale MD
Next Level Solutions, LLC
www.NextLevelSolns.com
919-846-9185

-------- Original Message --------
Subject: Re: [NMusers] algorithm limits
From: Leonid Gibiansky <LGibiansky Date: Sat, July 19, 2008 5:36 pm
To: Mark Sale - Next Level Solutions <mark Cc: www.quantpharm.com
e-mail: LGibiansky at quantpharm.com<= br> tel: (301) 767 5566




Mark Sale - Next Level Solutions wrote:
>
> General question:
> What are practical limits on the magnitude of OMEGA that is compatib= le
> with the FO and FOCE/I method? I seem to recall Stuart at one time > suggesting that a CV of 0.5 (exponential OMEGA of 0.5) was about the <= br> > limit at which the Taylor expansion can be considered a reasonable > approximation of the real distribution. What about FOCE-I?
> I'm asking because I have a model that has an OMEGA of 13, exponentia= l
> (and sometime 100) FOCE-I, and it seems to be very poorly behaved in <= br> > spite of overall, reasoable looking data (i.e., the structural model <= br> > traces a line that looks like the data, but some people are WAY above =
> the line and some are WAY below, and some rise MUCH faster, and some <= br> > rise MUCH later, by way I mean >10,000 fold, but residual error loo= ks
> not too bad). Looking at the raw data, I believe that the the
> variability is at least this large. Can I beleive that NONMEM FOCE > (FO?) will behave reasonably?
> thanks
> Mark
>