Alcuni modelli per l’analisi delle durate complete e incomplete della disoccupazione: il caso Emilia-Romagna

Sets of incomplete and completed spells of unemployment were obtained from the Italian Quarterly Labour Force Survey, carried out by ISTAT in Emilia-Romagna (1993:1--1995:1). The data were analysed through a proportional hazards model with a Weibull specification of the baseline hazard, including both unobserved heterogeneity applied to the scale parameter of the duration distribution, and telescoping effect to account for spikes in the distribution of unemployment spells. They were compared formally also with a non-proportional hazard model based on a log-logistic distribution of duration. The estimation of the parameters was carried out separately on both completed spells and quarterly incomplete spells to ascertain differences and to envisage the potential seasonal effect. The results showed that the shape parameters changed over time. The parameters of each covariate proved to be statistically stable over time and were also equal to the parameters of the completed spells model. Therefore, the analysis of incomplete spells is fairly feasible when an even (closed form) baseline hazard function is suitable for data.