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Re: [NMusers] unbalanced data set

From: Nick Holford <>
Date: Wed, 6 Jan 2016 21:00:46 +1300

I think you are imagining a problem that does not really exist. Each
observation contributes something to the overall fit. There is no
intrinsic reason to require "balance" across subjects. It is always
useful to have more information but it is not a good idea to remove
Best wishes,

On 06-Jan-16 15:03, Zheng Liu wrote:
> Dear all,
> I recently have a data set for pk parameters fitting. The issue is
> some patients have far more measurement points than others (i.e. a few
> patients have ~15 points, other patients have only 1 or 2). I
> speculate in the fitted parameters, those patients with many points
> would contribute much more than those with less points. Then the
> population "average" values of fitted pk parameters are not
> anymore average from all the patients, but more biased to those
> patients with many points. This is not what I expect.
> Of course I could take away some points from the patients with many
> points, in order to be comparable to less-points patients. Then I
> will be forced to lose some information from the data set. I just
> wonder are there anyone who have better proposal to solve this
> problem? I appreciate your help very much!
> Best regards,
> Zheng

Nick Holford, Professor Clinical Pharmacology
Dept Pharmacology & Clinical Pharmacology, Bldg 503 Room 302A
University of Auckland,85 Park Rd,Private Bag 92019,Auckland,New Zealand
office:+64(9)923-6730 mobile:NZ+64(21)46 23 53

"Declarative languages are a form of dementia -- they have no memory of events"

Holford SD, Allegaert K, Anderson BJ, Kukanich B, Sousa AB, Steinman A, Pypendop, B., Mehvar, R., Giorgi, M., Holford,N.H.G. Parent-metabolite pharmacokinetic models - tests of assumptions and predictions. Journal of Pharmacology & Clinical Toxicology. 2014;2(2):1023-34.
Holford N. Clinical pharmacology = disease progression + drug action. Br J Clin Pharmacol. 2015;79(1):18-27.

Received on Wed Jan 06 2016 - 03:00:46 EST

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