Evaluation of the Australian Wage Subsidy Special Youth ...

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proportion of time spent unemployed and number of siblings is controlled for using the
dummies. The estimation on the data where those cases with missing information in these
variables are dropped is given in Appendix Table A2.3. The results in columns one and
two are slightly different to that of Table 5.8. Of course the number of observations in
columns one and two of Appendix Table A2.3 are lower at 2150 because the observations
with missing information are dropped, whereas in Table 5.8 they are 2368. The Akaike
Information Criterion does not vary much in size between the models, and so does not
assist much in model selection here (because the sample and variables change between
the models, this fit measure is more relevant).The arguments of King et al. (2001) suggest
that dropping those cases, casewise deletion, gives the correct standard error, although
estimates do suffer the problems of bias. It is then a subjective choice as to whether the
analyst prefers to trade-off bias, however correct standard error estimation is essential if
the statistical significance of the coefficients is important to analysis. In light of this, it is
deemed more useful to apply casewise deletion than mean imputation dummies.
5.7.2 Sample reduction effects on model of SYETP participation
Columns 3 and 4 of Table 5.8 give the probit results for SYETP participation for the final
data set after sample reduction. Column 3 136 shows the unweighted results, and column 4
shows the results weighted with the survey weight. 137 As for the whole sample discussed
earlier, the variables that are statistically significant alter with the use of the weight. The
variables that gain significance when using the weight are married in 1984, attended a
private school, interviewed in Western Australia/ Tasmania, longest job held before 1984
was 3 years or more, mostly lived in a city until aged 14. The variables that lose
statistical significance are CEP referrals in 1984, father held a post-school qualification
when respondent aged 14, mother worked as plant operative when respondent aged 14. A
worrying change is the loss of statistical significance for CEP referrals in 1984. This is
further discussed later in the modelling of the treatment effect of SYETP, because this is
a key element of the identifying restriction in the bivariate probit of employment
136 The results in column 3 are equivalent to the univariate probit estimated in Richardson (1998).
137 Note that no account has been made of sample reduction from the 1984 survey in this weight. This is
treated next.