[R] Left censored responses in mixed effects models

[Bert Gunter]

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