st: generating a 0,1 variable which depends on lag values

[Christopher F Baum <baum@bc.edu>]

The solution to this issue presumably should involve a lag -- that is, 
"some positive action has been taken by an industry in the previous years." 
That would mean that Nisha's BB should not be contemporaneously 1, but 
should become 1 in the following year. A way to do that, starting with the 
year/industry/actions:

encode industry,gen(ind)
tsset ind year
bys ind: g sum=sum(actions)
g bb=L.sum>0 & L.sum<.

alternatively the last line could be written

g bb=L.sum>0  if L.sum<.

which would make bb missing in the first year of every firm. SInce bb 
refers to actions taken in prior years, perhaps that is more appropriate.

Kit

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