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st: RE: AW: Keep subsequent observations in panel data


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: AW: Keep subsequent observations in panel data
Date   Mon, 5 Oct 2009 16:09:24 +0100

This is neat, and can be compressed and slightly corrected further:

bys i:gen spell=_n
keep if t==spell

telescopes to 

bys i (t): keep if t==_n

The new variable -spell- is dispensable. 

-bysort i- is not quite error-proof. 

Nick 
n.j.cox@durham.ac.uk 

Martin Weiss

The first case should be as easy as


*************
clear*

inp byte(i) t y 
1      1     0 
1      2     0 
1      5     0 
1      6     0 
1      7     0 
1      8     0 
2      2     0 
2      5     0 
2      6     0 
2      7     0 
2      8     0 
end

compress

bys i:gen spell=_n
keep if t==spell
l, noobs sepby(i)

Nikolaos Kanellopoulos

I have a very simple unbalanced panel, where individuals are allowed to drop in and out of the sample. I want to create two separate datasets with  the following sampling criteria.

For the first one, individuals  that appear in the first wave should remain in the sample at subsequent years until the first time they drop out of the panel,
either completely or not. If they rejoin the panel later these observations should not be used. For instance in the following example I want to keep only observations 129 and 130.

+----------------------+
i   t   y 
----------------------
129.  1      1     0 
130.  1      2     0 
133.  1      5     0 
134.  1      6     0 
135.  1      7     0 
136.  1      8     0 
+----------------------+
137.  2      2     0 
138.  2      5     0 
139.  2      6     0 
140.  2      7     0 
141.  2      8     0 
+----------------------+

For the second dataset individuals should remain in the sample at subsequent years from the first time they are observed until the first time they drop out of the panel, either completely or return again. Again , if they rejoin the panel later these observations should not be used. For instance in the following example I want to keep only observations 129 to 130 and 137.

+----------------------+
i   t   y 
----------------------
129.  1      1     0 
130.  1      2     0 
133.  1      5     0 
134.  1      6     0 
135.  1      7     0 
136.  1      8     0 
+----------------------+
137.  2      2     0 
138.  2      5     0 
139.  2      6     0 
140.  2      7     0 
141.  2      8     0 
+----------------------+


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