A latent class model for the transition from school to working life in the presence of missing data

A longitudinal study on a cohort of pupils in the secondary school has been conducted in an Italian region since 1986 in order to study the transition from school to working life. The information have been collected at every sweep by a mail questionnaire and, at the final sweep, by a face-to-face interview, where retrospective questions referring back to the whole observation period have been asked. The gross flows between different discrete states - still in the school system, in the labour force without a job, in the labour force with a job - may then be estimated both from prospective and retrospective data, and the recall effect may be evaluated. Moreover, the conditions observed by the two different techniques may be regarded as two indicators of the 'true' unobservable condition, thus leading to the specification and estimation of a latent class model. In this framework, a Markov chain hypothesis may be introduced and evaluated in order to estimate the transition probabilities between the states, once they are corrected or the classification errors. Since the information collected by mail show a given amount of missing data in terms of unit nonresponse, the 'missing' category is also introduced in the model specification.