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st: lag


From   "Fabian Schönenberger" <[email protected]>
To   [email protected]
Subject   st: lag
Date   Thu, 31 May 2012 10:52:01 +0200

Dear Statalist
With the following command I want to generate a dummy variable; 1 if current sales are lower than 4 years ago, 0 if sales are larger for each company:

by cusip: generate sale_decrease5=0 if sale>sale[_n-4]
by cusip: replace sale_decrease5=1 if sale<=sale[_n-4]

I expected for each cusip 4 missings at the beginning, since there is no _n-4. However, the command gives 1 for each cusip in the first four years. 

How do I have to adapt the formula to get dummy variables after the first 4 years passed?

Many thanks in advance.

Fabian 
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