st: R: Including left-censored data in survival model

["Carlo Lazzaro" <carlo.lazzaro@tin.it>]

Dear Heidi,
some (not trivial) solutions about dealing with interval censoring are
reported in Cleves MA, Gould WW, Gutierrez RG. An Introduction to Survival
Analysis using Stata. Revised Edition. Stata Press, 2004: 32-33. 
In the following page (34), Authors stated that the same solutions can be
applied to left censoring, too.

Moreover, it would be probably interesting to explain which (if any)
covariates make the units gathered in a given category, as you report, more
likely to be left-censored.

Kindest Regards,
Carlo

-----Messaggio originale-----
Da: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] Per conto di Heidi
Inviato: venerdì 11 febbraio 2011 22.28
A: statalist@hsphsun2.harvard.edu
Oggetto: st: Including left-censored data in survival model

Hello all,

I'd like to estimate a Cox hazards model with my dataset, but it looks
like a good portion of my observations are left-censored and failed
in/prior to the first period. (I do have the year that they failed,
but no access to data prior to my time 0.) Having checked _st, it
looks like those subjects have already been dropped from the analysis.
However, these left-censored subjects were mostly also in a particular
category, so dropping them has made the other two categories seem much
more likely to fail.

Is there any way to include these dropped censored observations in the
analysis, at least for comparison to the analysis I'm already done?
Additionally, would there be a more appropriate model to examine
hazard ratios in this situation -- I'm reading through Cleves et al's
Intro to Survival Analysis, but have not (so far) found anything that
directly relates to this situation.

Thanks very much in advance!
Heidi
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