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Re: st: Computing Herfindahl-Hirschman index


From   Antoine Terracol <Antoine.Terracol@univ-paris1.fr>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Computing Herfindahl-Hirschman index
Date   Wed, 08 Dec 2010 12:35:19 +0100

Syed,

try

egen sum_item1=total(item1)
gen hhi_item1=(100*item1/sum_item1)^2

and so on for each item

or, alternatively

reshape long item, i(importer) j(id_item)

bysort id_item : egen sum=total(item)
gen hhi=item/sum
drop sum

reshape wide item hhi , i(importer) j(id_item)

which should give you all the results at once (I've not checked the code)

Antoine

On 08/12/2010 12:11, Syed Basher wrote:
Dear Statalist,

I have the following (hypothetical) trade dataset which contains imported items by importer.

importer  | item1 item2..... item20
-----------------------------------
11        |  10      20        80
12        |   5       7         9
13        |           1
14        |   2                 6
...       |
20        |   8       9

I would like to obtain the following table/data:

importer  | item1      item2   .... item20
-------------------------------------------
11        |  1600     2921.84       7091.41
12        |   400      357.92         89.75
13        |              7.30
14        |    64                     39.88
...       |
20        |  1024      591.67


where, say, the value 1600 is obtained using the formula (si*100)^2, where si is the share of importer11 in item1 and is obtained using 10/25,   25 is the sum of all entries in item1. This will allow me to get the  Herfindahl-Hirschman index by importer for each item.

I hope any one of you can help. Thank you so mcuh.

Regards,

Syed Basher
Qatar National Food Security Program




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