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st: RE: Herfindahl index

From   austin nichols <[email protected]>
To   [email protected]
Subject   st: RE: Herfindahl index
Date   Mon, 11 Jul 2005 11:58:40 -0400

You should read the help for genearate and egen, but before you can
implement the right commands, you will also want to nail down the
definition of the HHI:

egen double sasset=sum(asset), by(state year)
bysort state year: g double shsqrd= (asset/sasset)^2 
egen double HHI=sum(shsqrd), by(state year)

The above will be valid if you have a balanced panel.  Have you
thought about what to do for firms that enter or exit the panel, or
are missing data for intermediate years?

-----Original Message-----
From: Dawood Ashraf [mailto:[email protected]]
Sent: Monday, July 11, 2005 11:35 AM
To: [email protected]
Subject: st: Herfindahl index

I am trying to calculate degree of concentration in an industry by using the
Herfindahl index.  I am using the panel data where I have 10 years of time, 50
states, in every state there are a few companies. 

bysort  state: generate HERF= (asset/ sum(asset))^2 if repdte==1997

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