st: Syntax Question/ Cross-sectional Characteristic of a panel data

["ALICE DOBSON" <alice_dobson@hotmail.com>]

Hi all,
I have an unbalanced panel of firms for a period of 15 years, 1972-1986. One 
of the variables is Age of the firm. The maximum age of any firm is 15 
years. Hence, all firms are born during or after 1972. I want  to  compute  
the time of entry  of each firm, which will be one value for a particular 
firmid.

Firmid    Year    Age     Timeofentry
0001    1983     6         7
0001    1984     7
0001    1985     8
0001    1986     9
0002    1984     13      1
0002    1985     14
0002     1986    15


For instance, the age of firmid 0001 during the year 1983 [when it first 
appears in the data] is 6 years. I therfore compute its timeofentry as 7 
since it entered in 1978. Similarly, the age of firmid 0002 firmid during  
1984 [when it first appears in the data] was 13 and hence I compute its time 
of entry as  1.

I would like to compute the timeofentry of all firms in the unbalanced 
panel. Could anyone please help me with the syntax?

Best,
Alice

_________________________________________________________________
Is your PC infected? Get a FREE online computer virus scan from McAfee� 
Security. http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963

*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/