Please use this identifier to cite or link to this item: https://hdl.handle.net/10419/82294 
Year of Publication: 
2011
Series/Report no.: 
Working Paper No. 2011:26
Publisher: 
Institute for Labour Market Policy Evaluation (IFAU), Uppsala
Abstract: 
Shared-frailty survival models specify that systematic unobserved determinants of duration outcomes are identical within groups of individuals. We consider random-effects likelihood-based statistical inference if the duration data are subject to left-truncation. Such inference with left-truncated data can be performed in the Stata software package. We show that with left-truncated data, the commands ignore the weeding-out process before the left-truncation points, affecting the distribution of unobserved determinants among group members in the data, that is, among the group members who survive until their truncation points. We critically examine studies in the statistical literature on this issue as well as published empirical studies that use the commands. Simulations illustrate the size of the (asymptotic) bias and its dependence on the degree of truncation. We provide a Stata command file that maximizes the likelihood function that properly takes account of the interplay between truncation and dynamic selection.
Subjects: 
stata
duration analysis
left-truncation
likelihood function
dynamic selection
hazard rate
unobserved heterogeneity
twin data
JEL: 
C41
C34
Document Type: 
Working Paper

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