*Version October 2015
----------------------
basic syntax:

egi var, in(industry) st(state)index(#) mult(weight_var) by(year)

Description:

EGI calculates Ellision and Glaeser's index of geographical concentration of various 
industries. The module computes industry and region specific share of employment and 
also suitable for survey data where information up to plant level is available. EGI 
also evaluate other components of Ellision and Glaeser's index like square deviation 
of employment share  and Herfindhal index of plant level employment concentration. 

Ellision and Glaeser's index

EGIi = (GIi - HIi)/(1-HIi)

where, GIi = Sum of squared deivation of ith industry's state employment share from
a measure Ss. 

Ss = employment share ith state in the average industry. 

Hi = Herfindhal style measure of the plant level concentration of employment in ith 
industry. 

EGI syntax return and store the Ellision and Glaeser's index for each industry variety 
as a new variable. By choosing suitable index option it may also return other components. 
Option 
 

Option
-------
by(varlist): allows groups defined by `varlist' e.g. (year)

mult : allows for computing weighted index

Examples:
----------
egi worker , in(nic2) st(stcode) index(EGI) by(year) mult(mult)
egi worker , in(nic2) st(stcode) index(HHI) by(year)
egi worker , in(nic2) st(stcode) index(GI) 
egi worker , in(nic2) st(stcode) index(SS) 

Author:
Jay Dev Dubey
Jawaharlal Nehru University
New Delhi					
jaydevdubeyster@gmail.com

Acknowladgemnt:
---------------
Pritam Datta (PHFI)

References:
---------------

Ellison, Glenn, and Edward L. Glaeser. Geographic concentration in US manufacturing industries: 
a dartboard approach. No. w4840. National Bureau of economic research, 1994.

Dumais, Guy, Glenn Ellison, and Edward L. Glaeser. "Geographic concentration as a dynamic process." 
Review of Economics and Statistics 84.2 (2002): 193-204.