Dear stata list members,
I have a panel data of share of intra-firm imports (s_{ict}) where
observations vary over industry (i), country (c) and time (t). I need
to calculate the first difference of s_{ict}:
Delta_s_{ict}=s_{ict}-s_{ic(t-1)}.
I am not sure how to do this since I do not have a unique panel variable.
Also when using tsset how do I create unique id for each
industry-country pair (where both industry and country are string
variables). Any help would be appreciated.
My data is of the following form: Industry(Ind) and Country (Cty) are
both string variables
Ind Cty Yr
1 A 2000
1 B 2000
1 C 2000
1 A 2001
1 B 2001
1 C 2001
1 A 2002
2 A 2000
2 B 2000
2 D 2000
2X B 2001
2X A 2002
2X B 2002
Thanks in advance,
Best,
Modhura.
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