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st: About taking log on zero values


From   Sebastian Say <sebastian.statalist@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: About taking log on zero values
Date   Wed, 19 Feb 2014 13:44:15 -0600

Hi my question is about how stata treats a log-transformed variable
that draws upon an original variable that contains zero.

In my dataset, i have firm sales data but some of them have zero. I
created a logsales variable and noticed that those with zeros are
indicated as a "."

I plan to run a regression, e.g.

reg y x1 x2 logsales

My question is, how would stata treat these "." if I do not remove them?

Technically the "." should be undefined.

I've read some papers and they usually put a 1 for those sales data
with zeros in them. Is this a usual practice?

Thank you very much.

Seb
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