Re: st: RE: stset and the NLSY97

[Scott Cunningham <scunning@gmail.com>]

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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