title: Concordance measures in shared frailty models: application to clustered data in cancer prognosis.
abstract: Frailty models are gaining interest in prognostic studies, especially because of the spread of multicenter studies. However, little research has been performed to extend prognostic tools to frailty models, including discrimination measures. As previously performed for the Harrell's c-index, we extended two different discrimination measures (the model-based concordance probability estimation of Gönen and Heller and the nonparametric Uno's c-index) to take into account cluster membership. We calculate measures at three levels: between-group, where only patients with different frailties are compared, within-group, where only patients sharing the same frailty are compared, and overall. We performed simulations to study the impact of group size and the number of groups on these measures. Results showed that the two measures can be extended to frailty models while remaining independent from censoring distribution, provided that the group size is sufficient. We apply the extended measures to two real datasets, a meta-analysis and a large multicenter trial.
authors.affiliation: Univ. Bordeaux ISPED, Centre INSERM U897-Epidémiologie-Biostatistique, F-33000 Bordeaux, France; INSERM, ISPED, Centre INSERM U897-Epidémiologie-Biostatistique, F-33000 Bordeaux, France.
authors.forename: Audrey
authors.initials: A
authors.lastname: Mauguen
authors.forename: Sandra
authors.initials: S
authors.lastname: Collette
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Pignon
authors.forename: Virginie
authors.initials: V
authors.lastname: Rondeau
mesh_terms: D001943:Breast Neoplasms / Q000532:radiotherapy; D016000:Cluster Analysis; D003198:Computer Simulation; D005260:Female; D006258:Head and Neck Neoplasms / Q000188:drug therapy; D006801:Humans; D015233:Models, Statistical; D009369:Neoplasms / Q000473:pathology*; D011379:Prognosis
keywords: cancer; clustered data; concordance; frailty model; prognostic model