NONMEM Users Network Archive

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Re: advan8 vs. advan13 (CORRECTION)

From: Nick Holford <n.holford>
Date: Thu, 05 Nov 2009 12:42:44 +1300

Hi,

Thanks to Peiming Ma and Thuy Vu for pointing out an error in my attempt
to transform bioavailability into its logit.

The logit transformation of a probability is ln(P/(1-P)) i.e. the log of
the odds ratio. The reverse transform is correct i.e. exp(logit) is the
odds ratio and P is then OR/(1+OR) (or 1/1+exp(-logit)).

If THETA(1) is the bioavailability then this is (I hope) the correct
transformation of THETA(1) and reverse transform to get the individual
bioavailability with a random effect constrained to be within 0 and 1.

MU_1=LOG(THETA(1)/(1-THETA(1)) ; logit of population bioavailability
EXPP=MU_1+ETA(1) ; add random effect
BIO=1/(1+EXP(-EXP(EXPP))) ; individual bioavailability

Nick

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


Received on Wed Nov 04 2009 - 18:42:44 EST

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