HHI index (or any concentration / inequality index) from a tab command

[Jacopo Tramontano]

Hi, I'm trying to calculate HHI indexes starting from a tab command.
Manually, I just grab the percentages and put them in the new variable; but I wonder if there is a way to automate the process. In my data I have to do this 40 times (I have 2 sectors and 20 regions)!

sysuse auto
tab foreign
gen hhi=70.27^2 + 29.73^2
sum hhi

[Nick Cox]

Search the forum for mentions of HHI or of commands to calculate it such as entropyetc from SSC.

. sysuse auto, clear 

. entropyetc foreign, gen(4=HHI)

. l HHI in 1

     +----------+
     |      HHI |
     |----------|
  1. | .5821767 |
     +----------+

. tab foreign

 Car origin |      Freq.     Percent        Cum.
------------+-----------------------------------
   Domestic |         52       70.27       70.27
    Foreign |         22       29.73      100.00
------------+-----------------------------------
      Total |         74      100.00

. di 70.27^2 + 29.73^2
5821.7458

In your case, you presumably want to use the by() option. Multiplication by 10000 is something that you would have to do yourself.