st: How do I generate a matched sample with psmatch2 ?

["Frank Spiegel" <spiegel@wi.tum.de>]

Dear Statalist,

I want to create a matched sample in which I have patents owned by family firms and by non-family firms. In the beginning I have around 14,000 family firm patents and 90,000 non-family patents. For patents, it matters when the application was filed, which technology class they belong to etc. Now I would like to take each family patent and match one non-family patent from the same year and same technology class. Further I would like to match the patents, where the owning firms have the same size (for example assets). At the end I do not want any duplicates.

I have already tried the matching procedure with psmatch 2 with the following code:

psmatch2 familyfirm year class assets, neighbor(1) noreplacement

Unfortunately, the matching does not work that good. For example, I have a family firm patent from year 2000 but the matched non-family firm patent (identified with the new variable _id) is from year 2003, although it should be year 2000. The technology classes are also totally random.

Can anybody tell me, how you use the psmatch2 command correctly?

Thank you,
Frank


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