NONMEM Users Network Archive

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RE: Log transformation of imputed BQL

From: Rik Schoemaker <rik.schoemaker>
Date: Thu, 28 Jul 2016 06:57:16 +0000

Dear Manu,

NONMEM doesn't care about negative values when analysing data in the log do=
main. The sure-fire test is to do the analysis both after log-transforming =
in the original units, and after multiplying by 1000 as Dennis suggests, an=
d the results should be identical (if you adjust your afflicted starting va=
lues accordingly of course).

Kind regards,


Rik Schoemaker, PhD
Malandolaan 10
1187 HE Amstelveen
The Netherlands<>
+31 20 441 6410


From: owner-nmusers
 Behalf Of Dennis Fisher
Sent: 27 July 2016 23:26
To: Bharadwaj, Manushree <manushb
Cc: nmusers
Subject: Re: [NMusers] Log transformation of imputed BQL

one thing that you could do is multiply all the values by 1000 (i.e., chang=
e the units)

Dennis Fisher MD
P < (The "P Less Than" Company)
Phone / Fax: 1-866-PLessThan (1-866-753-7784)<>

On Jul 27, 2016, at 11:11 AM, Bharadwaj, Manushree <manushb<mailto:manushb

Dear friends,

I log transformed the plasma concentrations in my data and I am using this =
log transformed data as my dependent variable (DV). I imputed the BQLs to L=
LOQ/2, which is my case is (1/2=0.5). The natural log of 0.5 is negative =
which mean that I have negative values in my DV column.
While the parameter estimates look somewhat reliable, I have negative point=
s plotted in the diagnostic plots such as DV vs PRED, DV and PRED vs TIME, =
My questions are-
1. What is the best way of dealing with <1 DV/plasma concentration values w=
hile transforming into natural logarithm?
2. In my situation discussed above, where I have negative DV values in my d=
ata, has the NONMEM ignored or considered the negative numbers when estimat=
ing the parameter values?

Thank you,

With regards-
Manushree Bharadwaj, BVSc, PhD Candidate
Graduate Teaching Associate
Department of Physiological Sciences
Center for Veterinary Health Sciences
Oklahoma State University
Stillwater, OK-74074

(image/png attachment: image003.png)

Received on Thu Jul 28 2016 - 02:57:16 EDT

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