# NOT RUN {
## Estimate a simple female wage model taking into account the labour
## force participation
data(Mroz87)
a <- heckit(lfp ~ huswage + kids5 + mtr + fatheduc + educ + city,
log(wage) ~ educ + city, data=Mroz87)
## extract the full variance-covariance matrix:
vcov( a )
## now extract the variance-covariance matrix of the outcome model only:
vcov( a, part = "outcome" )
# }
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