Search results for "multivariate statistic"

gllvm: Fast analysis of multivariate abundance data with generalized linear latent variable models inr

2019

The work of J.N. was supported by the Wihuri Foundation. The work of S.T. was supported by the CRoNoS COST Action IC1408.F.K.C.H. was also supported by an ANU cross disciplinary grant.

Empirical Bayes improves assessments of diversity and similarity when overdispersion prevails in taxonomic counts with no covariates

2019

Abstract The assessment of diversity and similarity is relevant in monitoring the status of ecosystems. The respective indicators are based on the taxonomic composition of biological communities of interest, currently estimated through the proportions computed from sampling multivariate counts. In this work we present a novel method to estimate the taxonomic composition able to work even with a single sample and no covariates, when data are affected by overdispersion. The presence of overdispersion in taxonomic counts may be the result of significant environmental factors which are often unobservable but influence communities. Following the empirical Bayes approach, we combine a Bayesian mo…

Managing for resilience: an information theory-based approach to assessing ecosystems

2016

Ecosystems are complex and multivariate; hence, methods to assess the dynamics of ecosystems should have the capacity to evaluate multiple indicators simultaneously. Most research on identifying leading indicators of regime shifts has focused on univariate methods and simple models which have limited utility when evaluating real ecosystems, particularly because drivers are often unknown. We discuss some common univariate and multivariate approaches for detecting critical transitions in ecosystems and demonstrate their capabilities via case studies. Synthesis and applications. We illustrate the utility of an information theory-based index for assessing ecosystem dynamics. Trends in this inde…

Efficient estimation of generalized linear latent variable models.

2019

Generalized linear latent variable models (GLLVM) are popular tools for modeling multivariate, correlated responses. Such data are often encountered, for instance, in ecological studies, where presence-absences, counts, or biomass of interacting species are collected from a set of sites. Until very recently, the main challenge in fitting GLLVMs has been the lack of computationally efficient estimation methods. For likelihood based estimation, several closed form approximations for the marginal likelihood of GLLVMs have been proposed, but their efficient implementations have been lacking in the literature. To fill this gap, we show in this paper how to obtain computationally convenient estim…

Sampling effort and information quality provided by rare and common species in estimating assemblage structure

2020

Made available in DSpace on 2020-12-12T01:06:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-03-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Academy of Finland Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Reliable biological assessments are essential to answer ecological and management questions but require well-designed studies and representative sample sizes. However, large sampling effort is rarely possible, because it demands large financial resources and time, restricting the number of sites sampled, the duration of the study and the sampling effort at each site. In…

A multivariate morphometric analysis of diagnostic traits in southern Italy and Sicily pubescent oaks

2020

AbstractSpecies identification within the species complex ofQ. pubescensis a well-known taxonomic challenge among European botanists. Some of the specific pubescent oak binomials currently accepted in various European floras and checklists were originally described in Sicily and southern Calabria. As a consequence, several species belonging to the pubescent oaks group (Q. pubescens,Q. amplifolia,Q. congesta,Q. dalechampii,Q. leptobalanaandQ. virgiliana) are reported in the taxonomic and phytosociological literature. To verify whether it was possible to associate a diverse set of morphological characters with each of these different taxa, thirteen natural populations of pubescent oak from Si…

Dairy product consumption and risk of type 2 diabetes in an elderly Spanish Mediterranean population at high cardiovascular risk.

2015

PURPOSE The possible effects of dairy consumption on diabetes prevention remain controversial. The aim of this study was to investigate the association between the dairy consumption and type 2 diabetes (T2D) risk in an elderly Mediterranean population at high cardiovascular risk. METHODS: We prospectively followed 3,454 non-diabetic individuals from the PREDIMED study. Dairy consumption was assessed at baseline and yearly using food frequency questionnaires and categorized into total, low-fat, whole-fat, and subgroups: milk, yogurt, cheeses, fermented dairy, concentrated full fat, and processed dairy. Hazard ratios (HRs) were calculated using Cox proportional hazards regression models. RESU…

2020

Background Small sample sizes combined with multiple correlated endpoints pose a major challenge in the statistical analysis of preclinical neurotrauma studies. The standard approach of applying univariate tests on individual response variables has the advantage of simplicity of interpretation, but it fails to account for the covariance/correlation in the data. In contrast, multivariate statistical techniques might more adequately capture the multi-dimensional pathophysiological pattern of neurotrauma and therefore provide increased sensitivity to detect treatment effects. Results We systematically evaluated the performance of univariate ANOVA, Welch’s ANOVA and linear mixed effects models …

Lipid levels, atrial fibrillation and the impact of age:Results from the LIPIDOGRAM2015 study

2020

Background and aims: An inverse relationship between lipid levels and atrial fibrillation (AF) has been suggested, but whether the association is upheld for all age groups remains unclear. The aim of the study was to examine associations between lipid levels and AF by age groups in a nationwide study in Poland. Methods: Multivariate Poisson regression models were used to estimate prevalence ratios (PRs) for AF by lipid levels. Low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides (TG), total cholesterol (TC), non-HDL-C and LDL-C/HDL-C ratios were grouped into quartiles. Results: Of the 13,724 participants, 5.2% (n = 708) had AF. People with…

Factors influencing the development of visceral metastasis of breast cancer: A retrospective multi-center study.

2017

Abstract Purpose Visceral metastasis of breast cancer (BC) is an alarming development and correlates with poor median overall survival. The purpose of this retrospective study is to examine the risk factors for developing visceral metastasis by considering tumor biology and patient characteristics. Methods Using the BRENDA database, the risk factors such as histological and intrinsic subtypes of BC, age at primary diagnosis, grading, nodal status, tumor size and year of primary diagnosis were examined in univariate and multivariate analysis. Categorical variables were compared by using χ2 tests. Furthermore, multivariate Cox proportional hazards regression models, Kaplan–Meier product-limit…