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st: Date: Thu, 16 Nov 2006 13:37:35 -0500


From   "Visintainer, Paul" <PAUL_VISINTAINER@NYMC.EDU>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Date: Thu, 16 Nov 2006 13:37:35 -0500
Date   Thu, 16 Nov 2006 13:37:59 -0500 (EST)

Does anyone recall a command (similar to xtile or pctile) that creates a
new variable from an existing one, where the cutpoints are specific
percentages of the distribution?  (e.g., three groups created by
breaking the distribution at 37%, 62%, and 100%)


______________________________________
Paul F. Visintainer, PhD
Professor and Chair
Department of Epidemiology and Biostatistics
School of Public Health
New York Medical College
PH: (914) 594-4804
FX: (914) 594-4853
-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Daniel Simon
Sent: Thursday, November 16, 2006 1:15 PM
To: statalist@hsphsun2.harvard.edu; statalist@hsphsun2.harvard.edu
Subject: Re: st: left censoring in discrete-time duration model

Austin - thanks for the response.  In fact, I have done what you
propose. 
My point (3) where I said "I drop all observations from 1996 for firms
that
had websites" is actually what you are proposing, because once a firm
has 
established a website (transitioned), they are excluded from the
analysis 
sample thereafter.  I did not think about that when I wrote the
sentence. 
My apologies for not being clear. Thanks again for your response, which 
reminded me of what I was actually doing.

Moreover, as Austin says, I would also like to hear whether others also 
this is a sensible approach. thanks.

Daniel

At 12:00 PM 11/16/2006 -0500, Austin Nichols wrote:
>Daniel Simon--
>It seems to me that your estimates can only apply to introductions
>("failures") after 1996, since you cannot distinguish pre-1996 and
>1996 introductions, and you should drop firms (in all years) that had
>websites in 1996, while keeping data on all other firms from 1996,
>though I would be interested to hear from someone who actually runs
>these sorts of models, e.g. Stephen Jenkins.
>
>On 11/16/06, Daniel Simon <dhs29@cornell.edu> wrote:
>>Hi - I'm using -hshaz- to estimate a discrete-time hazard model. I
have
>>some left censoring that I'm not sure how to deal with. I am looking
at
>>firms establishing websites. I can only observe the introduction of
>>websites from 1996 onwards.  However, I know that some firms
established
>>websites prior to 1996, but I'm not sure which ones. Currently, I have
>>tried three approaches: (1) Treat all firms that had a website in 1996
as
>>if they adopted in 1996 (the first year of the sample period), whether
they
>>adopted in 1996 or adopted earlier; (2) Exclude 1996 from the sample
(begin
>>the analysis with 1997); (3) Drop all observations from 1996 for firms
that
>>had websites.
>>All three approaches give me quite similar results, so it does not
appear
>>that the censoring is a major issue. But, I'm wondering if there is a
>>better way to deal with it. Thanks. Daniel
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