Stima dei parametri della funzione di ripartizione dei periodi trascorsi: il caso dell'anzianità aziendale

Abstract

The duration data sets used to study employment or unemployment often come from samples of individuals at a point in time (Current Population Surveys) and they contain the lengths of ongoing spells of employment or unemployment for sample subjects who are currently employed or unemployed. These observations are right censored and are termed spells in progress or incomplete spells. The analysis of the raw data involves a length-biased estimate of spell durations. In this paper we examine the procedure to analyse the incomplete spells when the full lengths of spells, conditioned on their being in progress at the time of survey, are Weibull distributed. Particularly, the methodology of the estimation of the parameters is described for both the distribution function of spell duration and the proportional hazard model which include a set of explanatory variables (personal and job characteristics, local labour demand). Then, the methods are applied to the lengths of ongoing spells of employment for both employed workers and self-employed workers.