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Q:  

I am trying to merge a file with some restricted use items with the public use version of the data. I'm using stata. When I run the merge, I got a message saying "merge already defined."

Is this because some of the variable names are the same?

A:  

No. The message from stata says "_merge already defined."

_merge is an item that stata creates after a merge. It gives the user input on the outcome of the merge.

The possible values for _merge are:

1 - Observations from the master dataset that did not match observations from the using dataset
2 - Observations from the using dataset that did not match observations from the master dataset
3 - Observations from both datasets that did match

After looking at _merge you should either drop the item (drop _merge) or rename it (rename _merge merge1) as stata will not write over the existing _merge variable.

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