I assume you've looked at the NADA package(?) While I don't believe
it goes as far as dealing the mixed effects models, it might give you
a starting point, and possibly some additional references.
-Don
At 9:08 AM -0700 5/12/08, Bert Gunter wrote:
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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--
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062
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