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RE: Honest measurements

From: Mats Karlsson <mats.karlsson>
Date: Mon, 24 Aug 2009 12:53:07 +0200


And we need to design our studies to what is reported, which means taking
into account that for some observations, the only information you will get
is that they are below a limit.

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 Stephen Duffull
Sent: Monday, August 24, 2009 10:18 AM
To: Nick Holford; nmusers
Subject: RE: [NMusers] Honest measurements


I agree with Nick. Negative "observed" concns do occur for assays, even in
my limited time working with HPLC I have seen them, however due to LOD/LOQ
they are never really looked for and certainly never reported...


> -----Original Message-----
> From: owner-nmusers
> nmusers
> Sent: Monday, 24 August 2009 6:25 p.m.
> 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
> --
> Nick Holford, Professor Clinical Pharmacology
> Dept Pharmacology & Clinical Pharmacology
> University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New
> Zealand
> n.holford
> mobile: +64 21 46 23 53
Received on Mon Aug 24 2009 - 06:53:07 EDT

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