Re: st: left censoring in discrete-time duration model

["Daniel H. Simon" <dhs29@cornell.edu>]

Steven - I think you've misunderstood one point. I know the date when each 
print magazine was first published. I welcome any additional comments.

At 06:56 PM 11/28/2006, you wrote:

> On Nov. 28, 2006, at 2:05 PM, Austin Nicholas wrote:
>
> > I would argue that 1992 is a natural "zero" time for Daniel Simon's
> > project, since I am reasonably certain no magazines had websites
> > before 1992-
>
> As Austin, Stephen Jenkins, and I have suggested, Daniel is limited
> to analyses of firms without web sites in 1996 if he relies solely on
> the web archive. Now I am not sure he can even do that much with safety.
>
> Daniel:  Taking a start date of 1992, as Austin suggests, can you
> identify from other sources which magazines started publication after
> 1992 and the dates of publication? If you can, then as Stephen
> stated, then you can use likelihood methods. If you cannot, you have
> problems for which we have no good solution. It appears from your
> description that the web archive gives only the date of first
> appearance of the web-site. If so, what are you going to do about
> magazines which started publication after 1996?  For example, does a
> magazine with first web-site appearance in 2005 have nine years of
> "risk" or did the website and magazine start simultaneously in 2005?
> At the very least you should try to estimate the number of such
> magazines.
>
>
> Terminology: I disagree with Stephen that the data are "left- truncated." 
> I believe that they are primarily left-censored with
> possible left-truncation.  With left-truncated data the very
> existence of some observations is unknown because they take place too
> early.  The classic example is the fetal life table of miscarriages
> which did not record miscarriages that took place prior to the start
> of prenatal care.  In Daniel's archive, the analogous missed
> magazines are those which stopped publishing after 1992 and before
> 1996. (Here the very existence of the magazine, not just the web- site, is 
> unknown.)  For left-censored data (or for interval-censored
> data, in general), the analyst knows that the event took place
> between two dates. This is the case for the magazines in the archive
> with web sites in 1996, assuming that the dates for start of risk are
> known.
>
>
> Steven
>
>
> ________________________
> Steven Samuels
> 18 Cantines Island
> Saugerties, NY 12477
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>
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>
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>
>
>
>
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