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st: left censoring, survival analysis


From   "V. Martini" <vinmar0@hotmail.com>
To   Statalist <statalist@hsphsun2.harvard.edu>
Subject   st: left censoring, survival analysis
Date   Wed, 2 Sep 2009 11:20:59 +0100

Dear Stata Users,

I'm actually working on a sample of employed workers and I would like to know how to deal with left censoring in my data.

My sample contains employed workers in 1998, therefore I observe one spell per worker.

The end of the spells is found by using following waves.

The beginning of each employment spell can be found because workers have been asked when they started the current job. But unfortunately, this information is not known for workers that started their spell before 1979. My interpretation is that these workers should be treated as left censored, as the date when their spell begins is not known. I only know that their spell started before 1979.

My questions are:

1) Can I deal with these data in STATA or should I remove the left censored observations? In my sample, it seems that having left censoring and duration of the spell are positively correlated, therefore deleting these observations is likely to have consequences on inference.

2) Is the use of the module INTCENS (by Jamie Griffin) appropriate for these data?

3) The guide to Survival Analysis by Cleves, Gould and Gutierrez suggests that, even if possibly different in nature, matematically, left censored data can be treated as interval censored. In my case, I would observe one interval for each worker (intervals are very long and transitions occur at the end of the interval). Therefore, can I estimate my model using a probit / logit / cloglog model?

4) Finally, would st setting my data only indicating right censoring invalidate non parametric analysis (specifically, KM and NA estimates)?

Thanks,

Vinicio
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