st: Propensity score matching: Must all treated samples have a counterfactual?

[Ricky Lim <ricky.lim12345@gmail.com>]

Dear Statalisters,

I ran running propensity score matching using -pscore- and would like
to do radius & nearest neighbour matching (nearest 3 within +- x
score).
15 out of 20 of my treated samples have more than 3 counterfactuals
within 0.05 scores,
whereas the remaining 5 have 1 or none.
Their propensity scores are at the extreme and I would need to
increase the range to +-0.5 before they will have 3 counterfactuals
each.

My questions are:
1. Must every treated sample have a counterfactual / control?
2. Is a radius of 0.5 score too wide? Is it be acceptable to use the
nearest 3 within 0.5 score?

Any advice is deeply appreciated.

Thank you very much in advanced.

Regards,
Ricky
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