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Re: st: RE: stset and the NLSY97


From   Lars Kroll <lars@climweb.de>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: stset and the NLSY97
Date   Mon, 17 Oct 2005 09:24:23 +0200

I don't think your on the right way Marcello,

 id year age firstsex_yr
> > 1  1997 15     .
> > 1   1998 16   16
> > 1   1999 17   16
> > 1   2000 18  16
> > 2  1997 12   .
> > 2  1998  13  .
> > 2  1999  14 11
> > 2  2000 15  11
> > 3 1997  16  12
> > 3  1998  17  12
> > 3  1999 18  12
> > 3   2000 19  12

are single failure multiple obs per subject data, so I would suggest:

gen failure = age==firstsex if firstsex<.
sort persnr year
by persnr, sort : gen enterstudy = year==year[1] // if your first year
                                           // isn't 0 one never
                                           // know...

stset age, id(id) failure(failure==1) exit(failure==1)
enter(enterstudy==1)

Hope this helps,

Lars

Am Sonntag, den 16.10.2005, 21:46 -0400 schrieb Marcello Pagano:
> I do not understand your dilemma.  Assuming everyone is telling the truth,
> what you seem to have is time to first sex is your outcome of interest with
> the very Victorian identification of "death" as that time.  If someone is 17
> at the time of the survey without having had sex, then that is a censored
> observation.  So your "time" variable is firstsex_yr if sa==1
> and age if sa==0.   So you need to generate a variable
> 
> gen time = age
> replace time = firstsex_yr if sa==1
> stset time , failure(sa)
> 
> Your hazard should be zero for  time < = 10, but that
> depends on your data. You actually do have information back then, assuming
> you have done a decent job of sampling and things have not changed
> that much over the years. (By that I mean that if everyone you question
> is over 12, say, then their experience in the 0 to 12 time period is
> still representative of what is going in those years today.)
> 
> Hope this helps,
> 
> m.p.
> 
> Scott Cunningham wrote:
> 
> > On Oct 16, 2005, at 9:01 PM, Nick Cox wrote:
> >
> >> Not my field, but your dummy calculation can
> >> be put more succinctly:
> >>
> >> gen sa = firstsex_yr <= age
> >>
> >> However, safer would be to trap missings:
> >>
> >> gem sa = cond(mi(firstsex_yr, age), ., firstsex_yr <= age)
> >>
> >> Nick
> >
> >
> > Nick,
> >
> > Thanks for helping make the dummies more succinct.
> >
> > Do you think, though, that it is correct to use "age" as the actual  
> > duration variable?  So, for instance, I have a long dataset like this:
> >
> > id year age firstsex_yr
> > 1  1997 15     .
> > 1   1998 16   16
> > 1   1999 17   16
> > 1   2000 18  16
> > 2  1997 12   .
> > 2  1998  13  .
> > 2  1999  14 11
> > 2  2000 15  11
> > 3 1997  16  12
> > 3  1998  17  12
> > 3  1999 18  12
> > 3   2000 19  12
> >
> > So, by stsetting the data as so:
> >
> > .  stset age, failure(sa)
> >
> > where "sa" is an indicator equalling "1" if the person has become  
> > sexually active (signalling "death" in this context) and 0  
> > otherwise.  If I stset the data such that "age" is the duration, have  
> > I really made the right decision?  Or should I use "year" or should  
> > have some other variable that I create to correspond to time that has  
> > passed?  Because I really want to look at ten periods, initially -  
> > from 10 years to 19 years of age.  It's a short duration, relatively  
> > speaking, and most "exits" occur at 15-17.  So I don't actually have  
> > data for resopndents for those early, pre-survey, ages - ie, 10-12.   
> > So what's the best solution here?  Do I create a variable, maybe  
> > "time" or "virgin_time", that takes on a value of 1 to 10, and that  
> > variable matches up to the years that are covered in the data, and  
> > the years not covered?
> >
> > Is this post making sense?  I'm mainly just not sure of the proper  
> > way to execute this stset command to make use of the information I  
> > have in the form I currently have it in.
> >
> >
> > scott
> > *
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> 
> *
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-- 
Lars E. Kroll

Tutor für EDV & Statistik
Institut für Soziologie
Freie Universität Berlin

KONTAKT:
Email   mail@lkroll.de
Website www.lkroll.de

*
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