st: Using the maximum likelihood heckman - in the presence of missing variables

["georg wernicke" <georg.wernicke@googlemail.com>]

Hello,

I tried to use the maximum likelihood heckman and got the error term
r(504) saying that the hessian matrix has become unstable. most likely
that error term evolved since i, for some years, miss some independent
variables.

Do i have to use the heckman two step instead?

Thank you very much,

regards


georg wernicke
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