[R] Left censored responses in mixed effects models(II)

[Giovanni Parrinello]

Dear Bert,
you can also translate in nlme, as I'm trying to do, the approach of 
Thiébaut and *Gadda( *Mixed models for longitudinal left-censored 
repeated measures. Computer Methods and Programs in Biomedicine 74 
<http://www.informatik.uni-trier.de/%7Eley/db/journals/cmpb/cmpb74.html#ThiebautJ04>(3): 
<javascript:void(0)>(2004)) written in nlmixed(SAS)
Giovanni
Bert Gunter ha scritto:
> Dear R Fellow-Travellers:
>
> What is your recommended way of dealing with a left-censored response
> (non-detects) in (linear Gaussian) mixed effects models?
>
> Specifics: Response is a numeric positive measurement (of volume, actually);
> but when it falls below some unknown and slightly random value (depending on
> how the sample is prepared and measured), it cannot be measured and is
> recorded as 0. 
>
> There is some statistical literature on this, but I was unable to find
> anything that appeared to me to implement a strategy in any R package. If it
> matters, I am less interested in inference than in removing possible bias in
> estimation.
>
> Feel free to respond off-list if you feel that this would not be of general
> interest.
>
> Cheers,
>
> Bert Gunter
> Genentech
>
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>   


-- 
dr. Giovanni Parrinello
Department of Biotecnologies
Medical Statistics Unit
University of Brescia
Viale Europa, 11 25123 Brescia
email: parrinel at med.unibs.it
Phone: +390303717528
Fax: +390303717488