st: matching within groups

[Christoph Willing <christoph.willing@gmail.com>]

Dear Statalist,

I am trying to find a matching untreated company for each treated
company in my sample, based on pre-treatment firm characteristics.
My observations are grouped by country, industry and year, and the
matching should happen within a group.
I am not yet interested in the treatment effect, but simply want to
find the one nearest neighbour for each treated company that is most
similar in its firm characteristics.

I have run a pooled logit for the entire sample of the form "logit
treatment firm-characteristics" and predicted the propensity scores.
Now I am stuck at finding the nearest neighbours within the groups.
The matter is complicated by the fact that in some groups there are
more than one treated company.

Any help is greatly appreciated!
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