NONMEM Users Network Archive

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RE: Honest measurements

From: Mats Karlsson <mats.karlsson>
Date: Mon, 24 Aug 2009 11:53:53 +0200


So the advice regarding handling of error models actually concerns a study
that is to be done in your lab where negative concentrations are to be
reported. Not the million of studies with LOQ limits. Could have been useful
to know.

Best regards,

Mats Karlsson, PhD
Professor of Pharmacometrics
Dept of Pharmaceutical Biosciences
Uppsala University
Box 591
751 24 Uppsala Sweden
phone: +46 18 4714105
fax: +46 18 471 4003

-----Original Message-----
From: owner-nmusers
Behalf Of Nick Holford
Sent: Monday, August 24, 2009 8:25 AM
To: nmusers
Subject: [NMusers] Honest measurements

Mats Karlsson wrote:

<< Chemists, however pushed, would never report negative concentrations, not
for past studies, not for future studies. The methods they use don't even
report them.>>

I am working with a chemist using LC/MS who has been persuaded to look
honestly at his data without preconceived ideas of limits of quantitation
and detection. Indeed when he opened his eyes he found that his system was
indeed giving negative concentration measurements (at times when
concentrations were expected to be very low).

Of course we must do other things when the data is censored by bad
scientific practice in the chemist's lab but with honest measurments an
additive residual error model is required.


Nick Holford, Professor Clinical Pharmacology
Dept Pharmacology & Clinical Pharmacology
University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New Zealand
mobile: +64 21 46 23 53
Received on Mon Aug 24 2009 - 05:53:53 EDT

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