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In this paper we introduce robust techniques for inference and model selection in the analysis of longitudinal data. Robust versions of quasi-likelihood functions are obtained by building upon a set of robust estimating equations where robustness is achieved by weighting the classical estimating equations. The robust quasi-likelihood functions are then used(More)
Variable selection is an essential part of any statistical analysis and yet has been somewhat neglected in the context of longitudinal data analysis. In this article, we propose a generalized version of Mallows's C(p) (GC(p)) suitable for use with both parametric and nonparametric models. GC(p) provides an estimate of a measure of model's adequacy for(More)
S When using smoothing splines to estimate a function, the user faces the problem of choosing the smoothing parameter. Several techniques are available for selecting this parameter according to certain optimality criteria. Here, we take a different point of view and we propose a technique for choosing between two alternatives, for example allowing for(More)
OBJECTIVES This study investigates a potential increase in mortality and in the demand for ambulance emergency services among the elderly in particular, in Ticino in the summer of 2003. METHODS Mortality rates and emergency ambulance interventions rates were compared with records from the previous years. We considered the whole population, aged 65 and(More)
Longitudinal models are commonly used for studying data collected on individuals repeatedly through time. While there are now a variety of such models available (marginal models, mixed effects models, etc.), far fewer options exist for the closely related issue of variable selection. In addition, longitudinal data typically derive from medical or other(More)
Litter characteristics at birth were recorded in 4 genetic types of sows with differing maternal abilities. Eighty-two litters from F(1) Duroc x Large White sows, 651 litters from Large White sows, 63 litters from Meishan sows, and 173 litters from Laconie sows were considered. Statistical models included random effects of sow, litter, or both; fixed(More)
In this paper robust statistical procedures are presented for the analysis of skewed and heavy-tailed outcomes as they typically occur in health care data. The new estimators and test statistics are extensions of classical maximum likelihood techniques for generalized linear models. In contrast to their classical counterparts, the new robust techniques show(More)
OBJECTIVE To examine the evolution of psychosocial aspects of health-related quality of life in rheumatoid arthritis (RA) patients, and to identify their predictors. METHODS All patients within a Swiss RA cohort and a US RA cohort who completed a Short Form 36 (SF-36) scale at least twice within a 4-year period were included. The primary outcome was(More)