st: Heckman Procedure for Panel Data

[Prabal De <hereisprabal@gmail.com>]

Hi!
  I want to estimate a two-step model for an unbalanced dataset. I
found some entries with respect to Heckman procedure for Panel data,
but none of them seem to be resolved.
Can anyone tell me:
1) if there is a panel counterpart for heckman procedure?
2) What if we do the procedure ignoring the panel structure of the data?

 Thanks a lot in advance,
         Prabal
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