Multivariate Exponential Dispersion Models

Jørgensen, Bent; Martínez, José Raúl

doi:10.1142/9789814449403_0006

Cited by 37 publications

(65 citation statements)

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“…which is the general form for Tweedie distributions, where d is the dispersion parameter and p determines the specific class of distribution (Jorgensen, 1987). For all groups examined, p ranged between 1.07 and 1.83, which falls within the range of compound Poisson distributions.…”

Section: Statistical Model Of Photoreceptor Spectral Sensitivitymentioning

confidence: 80%

Ontogeny in the visual system of Nile tilapia

Sabbah

Hui

Hauser

et al. 2012

Journal of Experimental Biology

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SUMMARYRetinal neurogenesis in fish facilitates cellular rearrangement throughout ontogeny, potentially allowing for optimization of the visual system to shifts in habitat and behaviour. To test this possibility, we studied the developmental trajectory of the photopic visual process in the Nile tilapia. We examined ontogenetic changes in lens transmission, photoreceptor sensitivity and postreceptoral sensitivity, and used these to estimate changes in cone pigment frequency and retinal circuitry. We observed an ontogenetic decrease in ultraviolet (UV) photoreceptor sensitivity, which resulted from a reduction in the SWS1 cone pigment frequency, and was associated with a reduction in lens transmission at UV wavelengths. Additionally, post-receptoral sensitivity to both UV and long wavelengths decreased with age, probably reflecting changes in photoreceptor sensitivity and retinal circuitry. This novel remodelling of retinal circuitry occurred following maturation of the visual system but prior to reaching adulthood, and thus may facilitate optimization of the visual system to the changing sensory demands. Interestingly, the changes in post-receptoral sensitivity to long wavelengths could not be predicted by the changes observed in lens transmission, cone pigment frequency or photoreceptor sensitivity. This finding emphasizes the importance of considering knowledge of visual sensitivity and retinal processing when studying visual adaptations and attempting to relate visual function to the natural environment. This study advances our understanding of ontogeny in visual systems and demonstrates that the association between different elements of the visual process can be explored effectively by examining visual function throughout ontogeny.

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Section: Statistical Model Of Photoreceptor Spectral Sensitivitymentioning

confidence: 80%

Ontogeny in the visual system of Nile tilapia

Sabbah

Hui

Hauser

et al. 2012

Journal of Experimental Biology

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“…There are 2 Tweedie-distributed, 25 ie, ties at 0, variables (duration of untreated psychosis and untreated illness), which were evaluated by Mann-Whitney U test. Categorical variables were assessed with χ 2 tests.…”

Section: Discussionmentioning

confidence: 99%

Effectiveness of Integrated Care Including Therapeutic Assertive Community Treatment in Severe Schizophrenia Spectrum and Bipolar I Disorders

Schöttle

Schimmelmann

Karow³

et al. 2014

J. Clin. Psychiatry

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Objective:The ACCESS treatment model offers assertive community treatment embedded in an integrated care program to patients with psychoses. Compared to standard care and within a controlled study, it proved to be more effective in terms of service disengagement and illness outcomes in patients with schizophrenia spectrum disorders over 12 months. ACCESS was implemented into clinical routine and its effectiveness assessed over 24 months in severe schizophrenia spectrum disorders and bipolar I disorder with psychotic features (DSM-IV) in a cohort study. Method: All 115 patients treated in ACCESS (from May 2007 toOctober 2009) were included in the ACCESS II study. The primary outcome was rate of service disengagement. Secondary outcomes were change of psychopathology, severity of illness, psychosocial functioning, quality of life, satisfaction with care, medication nonadherence, length of hospital stay, and rates of involuntary hospitalization.Results: Only 4 patients (3.4%) disengaged with the service. Another 11 (9.6%) left because they moved outside the catchment area. Patients received a mean of 1.6 outpatient contacts per week. Involuntary admissions decreased from 34.8% in the 2 previous years to 7.8% during ACCESS (P < .001). Mixed models repeatedmeasures analyses revealed significant improvements among all patients in psychopathology (effect size d = 0.64, P < .001), illness severity (d = 0.84, P = .03), functioning level (d = 0.65, P < .001), quality of life (d = 0.50, P < .001), and client satisfaction (d = 0.11, P < .001). At 24 months, 78.3% were fully adherent to medication, compared to 25.2% at baseline (P = .002).Conclusions: ACCESS was successfully implemented in clinical routine and maintained excellent rates of service engagement and other outcomes in patients with schizophrenia spectrum disorders or bipolar I disorder with psychotic features over 24 months.Trial Registration: ClinicalTrials.gov identifier: NCT01888627

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“…Logistic and Poisson regression models for dealing with binary or binomial and count data, respectively. These models are linked, since they belong to the class of the exponential dispersion models (Jørgensen;1987, 1997, and share the property to be described by their first two moments, mean and variance. Furthermore, the variance function plays an important role in the context of exponential dispersion models, since it describes the relationship between the mean and variance and characterizes the distribution (Jørgensen;1997).…”

Section: Introductionmentioning

confidence: 99%

Flexible Tweedie regression models for continuous data

Bonat

Kokonendji

2017

Journal of Statistical Computation and Simulation

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Tweedie regression models provide a flexible family of distributions to deal with non-negative highly right-skewed data as well as symmetric and heavy tailed data and can handle continuous data with probability mass at zero. The estimation and inference of Tweedie regression models based on the maximum likelihood method are challenged by the presence of an infinity sum in the probability function and non-trivial restrictions on the power parameter space. In this paper, we propose two approaches for fitting Tweedie regression models, namely, quasi-and pseudo-likelihood. We discuss the asymptotic properties of the two approaches and perform simulation studies to compare our methods with the maximum likelihood method. In particular, we show that the quasilikelihood method provides asymptotically efficient estimation for regression parameters. The computational implementation of the alternative methods is faster and easier than the orthodox maximum likelihood, relying on a simple Newton scoring algorithm. Simulation studies showed that the quasi-and pseudo-likelihood approaches present estimates, standard errors and coverage rates similar to the maximum likelihood method. Furthermore, the secondmoment assumptions required by the quasi-and pseudo-likelihood methods enables us to extend the Tweedie regression models to the class of quasiTweedie regression models in the Wedderburn's style. Moreover, it allows to eliminate the non-trivial restriction on the power parameter space, and thus provides a flexible regression model to deal with continuous data. We provide R implementation and illustrate the application of Tweedie regression models using three data sets.

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Multivariate Exponential Dispersion Models

Cited by 37 publications

References 0 publications

Ontogeny in the visual system of Nile tilapia

Ontogeny in the visual system of Nile tilapia

Effectiveness of Integrated Care Including Therapeutic Assertive Community Treatment in Severe Schizophrenia Spectrum and Bipolar I Disorders

Flexible Tweedie regression models for continuous data

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