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st: calculate concentration ratio of four firms

From   "Alper [iso-8859-9] S÷nmez" <>
Subject   st: calculate concentration ratio of four firms
Date   Sun, 27 Dec 2009 16:42:54 +0200 (EET)

Hi, I want to calculate the first four firms share in each industry at
time t (HHI4 or CH4). I calculated the shares but i cannot sum first four
firms shares in each industry at time t.
I tried egen and gen commands with several functions  but they were not
Also i did not find any solution or material from stata books and online
I have an Unbalanced firm level panel data with variables id, years(t)
2003-2006, and 2digitsectors(Sector)and it is in long form

The problem:
I calculated
1stly, total sales of industry j at time t (Yjt)
2ndly, share of a firm i in industry j (sales of firm i/Yjt)*100=a
3rd a^2 for each firm at time t

4 step is problematic: I can not calculate shares of first four firms in
sector j at time t
like this max(a+a+a+a) by (sector year) and write this value for firms in
these sector and year

Please help me,

in advance thanks,

Alper Sönmez

ÝÝBF Ýktisat Bölümü/FEAS Department of Economics
Ankara Türkiye
Tel/Phone:0312 210 30 77
Fax: 0312 210 79 64

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