Evaluation of the Australian Wage Subsidy Special Youth ...

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this is mostly because there is no substantive selection to account for once weighted, as
evidenced by the hypothesis tests. This interpretation suggests that the sample attrition,
which affected the profile of characteristics including SYETP, may have acted as a form
of selection that the bivariate probit incorporated via selection into the program. As
section 5.6.1.1 showed, SYETP participation was associated with the data loss. As the
bivariate probit historically has been associated with applications where the data loss
from non-response has been accounted for in this way, this is not unreasonable. The
serious difficulties in obtaining an estimable specification for the bivariate probit are
highlighted by the failure of estimation for each of the alternative unweighted
specifications put forward. This indicates that the search for a suitable estimable
specification amongst plausible alternatives can be arduous. This can be a difficulty for
instrumental variables models, of which the Heckman bivariate probit is an example due
to the use of the exclusion restriction.