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[NMusers] Log transformation of imputed BQL

From: Bharadwaj, Manushree <manushb_at_ostatemail.okstate.edu>
Date: Wed, 27 Jul 2016 14:11:39 -0400

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
LLOQ/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
points plotted in the diagnostic plots such as DV vs PRED, DV and PRED vs
TIME, etc.
My questions are-
1. What is the best way of dealing with <1 DV/plasma concentration values
while transforming into natural logarithm?
2. In my situation discussed above, where I have negative DV values in my
data, has the NONMEM ignored or considered the negative numbers when
estimating the parameter values?

Thank you,
Manu

--
*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*

Received on Wed Jul 27 2016 - 14:11:39 EDT

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