st: psm question

[俊利,俞 Junli-Yu <jlyuchina@gmail.com>]

Dear Statalister,

     My  master sample(50 obs.), the pairs sample(200 obs.)

      I use “psmatch2” command:

//

cap drop u

           set seed 500

      g  u = runiform()

      sort u

      psmatch2 X ControlVar , neighbor(1)  logit

      order X ControlVar _pscore- _pdif

      pstest ControlVar

drop if _weight==.//



my question is the support/matched pairs sample(only 35 obs.) is less
than master sample(50 obs.).

Why? how to solve this problem that make the matched sample is 50.

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