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Richardson (1998) is then extended here, by estimating the attrition of the Australian
Longitudinal Survey and constructing weights to reduce the resultant bias. This also
serves as a test of the impact of attrition bias on the estimated results.
5.5 Examining the role of attrition in the ALS and in modelling of the SYETP
employment effect
To assess the issue of attrition bias a set of analyses are conducted, drawing on the tests
of Fitzgerald et al. (1998a). Firstly, the univariate effects of attrition upon means are
examined. The Fitzgerald et al. (1998a) framework for the statistical analysis of attrition
bias applied here focuses upon sample attrition which results in selection on observables.
The case for attrition due to observables is examined for the ALS by investigating the
observed means. The effects of attrition upon the models of SYETP participation are also
considered. The probability of attrition is then modelled using the probit. Weighting
effects upon the model of employment outcomes for the SYETP programme are
additionally explored.
5.5.1 Extent of sample reduction
The ALS list sample was constructed from administrative records of persons aged 15-24
on 1 September 1984. The sample was selected based on those registered with the
Commonwealth Employment Service offices throughout Australia who were unemployed
and seeking full-time work for three months or more at the time of selection in June 1984.
The original sample had 2998 cases, and the first survey collected interviews from 2,403
cases.
Interviews for the first survey were conducted between September 1984 and November
1984. The survey was repeated in each of the later years 1985, 1986 and 1987, following
up the same people with whom interviews were conducted in 1984. In 1985 1,910
interviews were conducted in the months June to October, in 1986 1,711 interviews were
collected between September and November, and in 1987 1,518 interviews repeated