Merge file

[Heidi Ph]

Hello,

I am reading instruction on merging files on stata in this link:
https://www.stata.com/manuals13/dmerge.pdf

It explains the option "nogen" as: "do not create _merge variable"

I do not understand what does this mean? what is the _merge variable?

Is there anyone having an idea?

Thanks for your help in advance!

[Clyde Schechter]

By default, -merge- creates a new variable, _merge, in the combined data set that takes on the values 1 for observations that were found in the master data only, 2, for observations found only in the using data, and 3 for observations that were found in both data sets and paired up in the merge. (There are also values 4 and 5 if the -update- or -replace- options were specified.) It is this variable that -nogenerate- will suppress.