st: Generate a new variable [four firm concentration ratio]

["ALICE DOBSON" <alice_dobson@hotmail.com>]

Dear all,
I use stata 9.1

I have an unbalanced panel data of the type:

geographical region (m = 1..1154)
year (t = 1..7)

with the following variables:

total number of consumers in each region (CONSUM_mt)
total number of consumers of seven firms in each region (F1_mt, F2_mt, 
F3_mt, F4_mt, F5_mt, F6_mt, F7_mt)


I want to calculate the four firm concentration ratio for each region, 
C4_mt, which is the proportion of the number of consumers of top four firms 
to the total number of consumers in that region, in percentage

Could anyone be kind enough to help me with this simple calculation?

Best,
Alice.


GEOGREGN YEAR CONSUM F1 F2 F3 F4 F5 F6 F7 C4
M1 1969
M1  1970
M1  1971
M1  1972
M1  1973
M1  1974
M1  1975
M2 1969
M2  1970
M2  1971
M2  1972
.
.
.
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.
.

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