Evaluation of the Australian Wage Subsidy Special Youth ...

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5.5.2 Univariate examination of sample reduction
Table 5.2 gives a univariate analysis of the differences between the characteristics of the
final sample and those who are lost from the sample. This expands the information
provided in Table 1 of Richardson (1998) by including the t-test of statistical significance
for the difference between the mean of the remaining sample and those lost. Column 1
shows the mean for the final sample, and corresponds to column 1 of Table 1, Richardson
(1998). Allowing for rounding, the means are identical to those presented in Richardson.
This is seen as a check that the final data matches that of Richardson (1998). The second
column gives the standard deviation. Column 3 gives the mean of those lost from the
sample, with column 4 the standard deviation. The absolute difference in the mean is
given in the fifth column, with the t statistic in the sixth column. The t test of the
hypothesis that the difference in the means is zero, accommodating unequal variance in
the samples, is shown in column 6, with significance levels of 10 per cent, 5 per cent and
1 per cent indicated with 1, 2 and 3 stars in each case. A number of outcome and
regressor variables are shown. Most of these are useful variables in the modelling of
employment outcomes. All the variables are identified using the 1984 survey data, except
‘ever employed in 1986’, and ‘ever on a government programme in 1986’, the first of
which is a dependent variable for analysis. SYETP participation is an important variable
that is an outcome defined in the 1984 survey.
Table 5.2 compares those remaining in the final sample to all those lost from the final
sample. It is important to note that this does not differentiate between those cases lost due
to non-response at surveys in 1985, 1986 and those cases dropped in the analytical
selection process. The aim of initially examining the effect of sample loss on the means
observed is not affected by this combination. The different sources of sample loss are
subsequently dealt with separately in the further analysis of attrition.
The two variables ‘ever employed in 1986’, and ‘ever on a government programme in
1986’ suffer from the ‘selection by survival’ problem. The parts of the sample lost due to