Nick, 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 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-nmus...@globomaxnm.com [mailto:owner-nmus...@globomaxnm.com] On 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 -- Nick Holford, Professor Clinical Pharmacology Dept Pharmacology & Clinical Pharmacology University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New Zealand n.holf...@auckland.ac.nz tel:+64(9)923-6730 fax:+64(9)373-7090 mobile: +64 21 46 23 53 http://www.fmhs.auckland.ac.nz/sms/pharmacology/holford
