Dear Statalisters,
I’m working with a panel data and I
have a little question.
I have observations for firms’
R&D expenditures for 8 years.
I would like to keep observations for
all that firms that performs or has performed
R&D during at least one year (R&D
expenditures>0 for at least one year).
How can i do this? I don’t want drop
all observations with R&D==0 I want drop only firms whose R&D
expenditures has been equal to 0 for all
years, and keep all observations of firms that
had performed R&D for at least one
year, including these observations with R&D==0 for some years.
Thank you very much,
Sergio
