Estimating survival under a dependent truncation
1 Département de mathématiques et de statistique, Université Laval, Ste-Foy, Québec, G1K 7P4 Canada. lakhal{at}mat.ulaval.ca, lpr{at}mat.ulaval.ca, 2 Département de médecine sociale et préventive, Université Laval, Ste-Foy, Québec, G1K 7P4 Canada. belkacem.abdous{at}msp.ulaval.ca
The product-limit estimator calculated from data subject to random left-truncation relies on the testable assumption of quasi-independence between the failure time and the truncation time. In this paper, we propose a model for a truncated sample of pairs (Xi,Yi) satisfying Yi > Xi. A possible dependency between the truncation time and the variable of interest is modelled with a parametric family of copulas. The model also features a distribution function FX(.) and a survival distribution SY(.) associated with the marginal behaviours of X and Y in the observable region Y > X. Semiparametric estimators for these two functions are proposed; they do not make any parametric assumption about either FX(.) or SY(.). We derive an estimator for the copula parameter
based on the conditional Kendall's tau. We generalise the copula-graphic estimators of Zheng & Klein (1995) to truncated variables. The asymptotic distributions of all these estimators are then investigated. The methods are illustrated with a real dataset on HIV infection by transfusion and by simulations.
Key Words: Copula; Kaplan-Meier estimator; Kendall's tau; U-statistic.
Received October 2004. Revised February 2006.