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|Title:||Marginal correlation from an extended random-effects model for repeated and overdispersed counts||Authors:||VANGENEUGDEN, Tony
Demetrio, Clarice G. B.
|Issue Date:||2011||Publisher:||ROUTLEDGE JOURNALS, TAYLOR & FRANCIS LTD||Source:||JOURNAL OF APPLIED STATISTICS, 38 (2). p. 215-232||Abstract:||Vangeneugden et al.  derived approximate correlation functions for longitudinal sequences of general data type, Gaussian and non-Gaussian, based on generalized linear mixed-effects models (GLMM). Their focus was on binary sequences, as well as on a combination of binary and Gaussian sequences. Here, we focus on the specific case of repeated count data, important in two respects. First, we employ the model proposed by Molenberghs et al. , which generalizes at the same time the Poisson-normal GLMM and the conventional overdispersion models, in particular the negative-binomial model. The model flexibly accommodates data hierarchies, intra-sequence correlation, and overdispersion. Second, means, variances, and joint probabilities can be expressed in closed form, allowing for exact intra-sequence correlation expressions. Next to the general situation, some important special cases such as exchangeable clustered outcomes are considered, producing insightful expressions. The closed-form expressions are contrasted with the generic approximate expressions of Vangeneugden et al. . Data from an epileptic-seizures trial are analyzed and correlation functions derived. It is shown that the proposed extension strongly outperforms the classical GLMM.||Notes:||[Vangeneugden, Tony; Molenberghs, Geert; Verbeke, Geert] Hasselt Univ, Ctr Stat, Diepenbeek, Belgium. [Vangeneugden, Tony] Johnson & Johnson, Tibotec, Mechelen, Belgium. [Molenberghs, Geert; Verbeke, Geert] Katholieke Univ Leuven, Ctr Biostat, Louvain, Belgium. [Demetrio, Clarice G. B.] ESALQ, Sao Paulo, Brazil. email@example.com||Keywords:||intraclass correlation; maximum likelihood; negative-binomial model; Poisson model; random effects; repeated measures;intraclass correlation; maximum likelihood; negative-binomial model; Poisson model; random effects; repeated measures||Document URI:||http://hdl.handle.net/1942/11833||ISSN:||0266-4763||e-ISSN:||1360-0532||DOI:||10.1080/02664760903406405||ISI #:||000286976100001||Rights:||© 2011 Taylor & Francis||Category:||A1||Type:||Journal Contribution||Validations:||ecoom 2012|
|Appears in Collections:||Research publications|
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