Centro de Ciências Exatas e da Terra

URI Permanente desta comunidadehttps://repositorio.ufrn.br/handle/1/135

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Testing homogeneity in Weibull-regression models
(Biometrical Journal, 2005) Bolfarine, Heleno; Valença, Dione M.
In survival studies with families or geographical units it may be of interest testing whether such groups are homogeneous for given explanatory variables. In this paper we consider score type tests for group homogeneity based on a mixing model in which the group effect is modelled as a random variable. As opposed to hazard-based frailty models, this model presents survival times that conditioned on the random effect, has an accelerated failure time representation. The test statistics requires only estimation of the conventional regression model without the random effect and does not require specifying the distribution of the random effect. The tests are derived for a Weibull regression model and in the uncensored situation, a closed form is obtained for the test statistic. A simulation study is used for comparing the power of the tests. The proposed tests are applied to real data sets with censored data.
Testing homogeneity inWeibull error in variablesmodels
(Wiley, 2006) Valença, Dione Maria; Bolfarine, Heleno
Wediscusspropertiesofthescorestatisticsfortestingthenullhypothesis ofhomogeneityinaWeibullmixingmodelinwhichthegroupeffectismodelledas arandomvariableandsomeofthecovariatesaremeasuredwitherror.Thestatistics proposed are based on the corrected score approach and they require estimation onlyundertheconventionalWeibullmodelwithmeasurementerrorsanddoesnot require that the distribution of the random effect be speciﬁed. The results in this paperextendresultsinGimenez,Bolfarine,andColosimo(AnnalsoftheInstitute ofStatisticalMathematics,52,698–711,2000)forthecaseofindependentWeibull models.Asimulation study is provided.

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