Evaluation of the Australian Wage Subsidy Special Youth ...

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Table 5.5a draws a distinction between the sources of sample reduction amongst those
dropped for the analysis –the 140 cases dropped for having missing information on
variables used in analysis and the 264 cases dropped for other analytical reasons. 126 Table
5.5a shows the means, standard deviation, absolute difference and t test of the
significance of the difference from zero, using the same layout as for Table 5.5. The first
two columns of Table 5.5a show the mean and standard deviation in the final sample, to
which the two sources of sample reduction are compared in the t-test of the significance
of the difference from zero. The next four columns make up the first panel of the table
which relates to the sample lost due to missing information, and they show the mean,
standard deviation, absolute difference in the means and the t statistic, in a similar fashion
to the former tables. The second panel gives the statistics for those lost though further
analytical selection. Only differences that are statistically significant at normally adopted
confidence levels are discussed.
Amongst those cases dropped because certain variables used in analysis are missing
information, it is first noticeable that case-wise deletion in this manner leads to the loss of
information from the whole case. For example ‘father post-school qualification’ is
present for 79 of the 140 cases dropped, but while the missing information for ‘father
post-school qualification’ was the reason for the 61 cases being dropped, these extra 79
cases are dropped due to other variables having missing information. It is then very much
an ‘all or nothing strategy’, where more information is lost than is actually missing.
Column 5 of Table 5.5a indicates the number of cases that were missing information, at
most 140. It can be seen from Table 5.5a that amongst those where all 140 cases had
missing information for the variable in question, that for some of the variables the
missing had a different profile to those remaining in the final sample. As a result, those
dropped for case-wise deletion to treat missing information had undertaken less SYETP
treatment, more often had children, less often had highest qualification of year 12 or year
11, were much less often in employment in 1986, had more health problems affecting
work, and came less often from Victoria and Queensland and more often from Western
126 There are 404 cases dropped for analytical reasons, of which there are 140 cases where at least one of
the variables used in the analysis is missing for a case, then a further 264 cases are dropped for other
analytical reasons.