Search results for "GLMM"
showing 10 items of 16 documents
Reference growth charts for Posidonia oceanica seagrass: An effective tool for assessing growth performance by age and depth
2016
Abstract Growth performance of rhizomes has become among the most used descriptors for monitoring Posidonia oceanica seagrass dynamics and population status. However, ability to detect any change of growth in space or in time is often confounded by natural age-induced decline. To overcome this problem, we have produced reference growth charts, which in other areas are universally recognized as a very powerful tool for comparing growth of living beings during their ontogeny. Reference growth charts involving different P. oceanica growth performance measures (speed of growth and primary production of rhizomes) have been built using proper statistical frameworks (GLMM, Segmented and Quantile R…
Model interpretation from the additive elements of the PWRSS in GLMMs
2013
Generalized Linear Mixed models(GLMMs)have rapidly become a widely used tool for modelling clustered and longitudinal data with non-Normal responses. Although a large amount of work has been done in the literature on likelihood-based inference on GLMMs,little seems to have been done on the decomposition of the total variability associated to the different components of a mixed model.In this work we try to generalize the idea of likelihood additive elements Whittaker,1984), proposed in the context of GLMs,to the case of GLMMs by using the Penalized Weighted Residual Sum of Squares(PWRSS). The proposal is illustrated by means of areal application.
“You look at it, but will you choose it”: Is there a link between the foods consumers look at and what they ultimately choose in a virtual supermarke…
2022
Most of the studies that showed a link between gaze allocation and consumer's food choices were performed on food products belonging to a same category. However, consumers usually make food choices in more complex environments, between many different products, and different factors can influence their choices. Therefore, our study aimed to understand the link between gaze behavior and food choices in a complex and realistic situation of choice. Participants (n=99) performed a food choice task in a virtual supermarket. They had to choose three food products to create a dish in four scenarios evoking different motivations (focus on health, environment, food pleasure, and daily scenario as con…
Influence diagnostics for generalized linear mixed models: a gradient-like statistic
2013
In the literature, many influence measures proposed for Generalized Linear Mixed Models (GLMMs) require the information matrix that can be difficult to calculate. In the present paper, a known influence measure is approximated to get a simpler form, for which the information matrix is no more necessary. The proposed measure is showed to have a form similar to the gradient statistic, recently introduced. Good performances have been obtained through simulation studies.
Reference growth charts for assessing growth performance of Posidonia oceanica (L.) Delile
2016
Posidonia oceanica is considered a key species due to its different roles as primary producer, substrate for many species, shoreline erosion protector and long-term carbon store (1).The importance of P. oceanicahas stimulated several studies aimed at quantifying its status. In particular growth performance of rhizomes has become among the most used descriptors for monitoring changes of P. oceanicameadows induced by human or naturalexogenous factors (2). However, ability to detect any change of growth in space or in time is often confounded by natural age-induced variations, which involves serious interpretation problems (3). A general approach adopted to overcome this problem is to build gr…
Prediction of the gene expression measure by means of a GLMM
2007
Microarrays permit to scientists the screening of thousands of genes simultaneously to determine, for example, whether those genes are active, hyperactive or silent in normal or cancerous tissues. A primary task in microarray analysis is to obtain a good measure of the gene expression that can be used for a so called higher level analysis. Different methods have been proposed for high density oligonucleotide arrays (see Cope et al. (2004) for a review). Aim of this paper is to obtain a new gene expression measure based on the background correction model proposed by Mineo et al. (2006). The proposed method is validated by means of a free available data-set called Spike-In133 experiment, wher…
Modeling Ordinal Item Responses via Binary GLMMs and Alternative Link Functions: An Application to Measurement of a Perceived Service Quality
2010
Evaluation of a service on the basis of consumer opinion is a widespread practice in many fields. The assessment of perceived quality [7] of a service is generally carried out through administration of a questionnaire, composed of several items with responses posed on an ordinal scale, whereby each item represents an important feature of the evaluated service [3, 7]. In this context, the aim is to evaluate something similar to the external effectiveness, that is the part of efficacy related to the satisfaction expressed by the service users for the provided service. A particular and important example of service users is represented by students’ responses measuring the perceived quality of s…
Effect of different substrata on rhizome growth, leaf biometry and shoot density of Posidonia oceanica
2013
The effects of different substratum typologies on Posidonia oceanica growth and morphology were estimated in four Sicilian meadows using Generalized and Linear Mixed Models combined with retrodating and biometric analyses. Substratum exerted a multiple effect, resulting in different biometric features for P. oceanica shoots settled on rock from those growing on sand and matte. On rock, values for growth rate, leaf length and shoot surface were lower than those on other substrata, with 42%, 23% and 32% the highest degree of difference respectively. The present study may have interesting methodological consequences for the comprehensive understanding of the causative variables potentially aff…
Modeling temporal and spatial colony‐site dynamics in a long‐lived seabird
2003
We studied the determinants of colony site dynamics in Audouin's gull, Larus audouinii, breeding in a small archipelago of the western Mediterranean. Data on island occupation were available for a series of 25 years, since first colonization of the archipelago in 1973. Group behavior was studied in relation to the components of dispersal: permanence or abandonment (extinction) on an island previously occupied and permanence or occupation (colonization) of another island. Generalized Linear Mixed Models (GLMMs) were used to identify the relative contribution of each explanatory variable to the probability of colony abandonment. Gulls showed a low probability (3%) of abandoning one of the isl…
A model-based approach to Spotify data analysis: a Beta GLMM
2020
Digital music distribution is increasingly powered by automated mechanisms that continuously capture, sort and analyze large amounts of Web-based data. This paper deals with the management of songs audio features from a statistical point of view. In particular, it explores the data catching mechanisms enabled by Spotify Web API and suggests statistical tools for the analysis of these data. Special attention is devoted to songs popularity and a Beta model, including random effects, is proposed in order to give the first answer to questions like: which are the determinants of popularity? The identification of a model able to describe this relationship, the determination within the set of char…