# Re: st: calculate concentration ratio of four firms

 From "Martin Weiss" To statalist@hsphsun2.harvard.edu Subject Re: st: calculate concentration ratio of four firms Date Sun, 27 Dec 2009 19:28:19 +0100

```Give an excerpt of your data to enable the list to answer! -egen- takes expressions, so you can easily condition on the firms being among the first four.

HTH
Martin
-------- Original-Nachricht --------
> Datum: Sun, 27 Dec 2009 16:42:54 +0200 (EET)
> Von: "Alper [iso-8859-9] Sönmez" <salper@metu.edu.tr>
> An: statalist@hsphsun2.harvard.edu
> Betreff: st: calculate concentration ratio of four firms

> 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
> worked
> Also i did not find any solution or material from stata books and online
> resources
> 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
>
>
>
>
>
>
>
> --
> Alper Sönmez
>
> ODTÜ/METU
> ÝÝBF Ýktisat Bölümü/FEAS Department of Economics
> Ankara Türkiye
> Tel/Phone:0312 210 30 77
> Fax: 0312 210 79 64
>
>
>
>
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```