A combined gamma frailty and normal random-effects model for repeated, overdispersed time-to-event data

• Published in: Statistical methods in medical research Vol. 24; no. 4; pp. 434 - 452
• Main Authors: Molenberghs, Geert, Verbeke, Geert, Efendi, Achmad, Braekers, Roel, Demétrio, Clarice GB
• Format: Journal Article
• Language: English
• Published: London, England SAGE Publications 01.08.2015; Sage Publications Ltd
• Subjects: Adult; Asthma; Asthma - physiopathology; Cancer; Child, Preschool; Data Interpretation, Statistical; Female; Humans; Likelihood Functions; Male; Marginality; Models, Statistical; Neoplasms - physiopathology; Random effects; Recurrence; Recurrent; Simulation; strong conjugacy; conjugacy; maximum likelihood; frailty model; Weibull model; generalized Cauchy distribution; pseudo-likelihood; exponential model
• ISSN: 0962-2802; 1477-0334; 1477-0334
• DOI: 10.1177/0962280214520730

This paper presents, extends, and studies a model for repeated, overdispersed time-to-event outcomes, subject to censoring. Building upon work by Molenberghs, Verbeke, and Demétrio (2007) and Molenberghs et al. (2010), gamma and normal random effects are included in a Weibull model, to account for overdispersion and between-subject effects, respectively. Unlike these authors, censoring is allowed for, and two estimation methods are presented. The partial marginalization approach to full maximum likelihood of Molenberghs et al. (2010) is contrasted with pseudo-likelihood estimation. A limited simulation study is conducted to examine the relative merits of these estimation methods. The modeling framework is employed to analyze data on recurrent asthma attacks in children on the one hand and on survival in cancer patients on the other.