Search results for "GLM"
showing 10 items of 36 documents
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…
Smiltāja neļķes (Dianthus arenarius) izplatības modelēšana pelēkajās kāpās izmantojot attālās izpētes datus
2016
Smiltāja neļķe (Dianthus arenarius) ir Latvijā reti sastopama, aizsargājama vaskulāro augu suga. Tās pasuga Dianthus arenariu subsp. arenarius ir aizsargājama visā Eiropas Savienības (ES) līmenī. Lai būtu iespējams mainīt esošo situāciju, nepieciešams iegūt vairāk datu par sugas izplatību ietekmējošajiem faktoriem, kā arī noskaidrot iespējamās smiltāja neļķu augšanas vietas, ar mērķi precizēt sugas populācijas lielumu. Mūsdienās nereti sugu iespējamā izplatība pētāmajā teritorijā tiek modelēta, balstoties uz attālās izpētes datiem. Lai noskaidrotu smiltāja neļķes izplatību ietekmējošos faktorus, Užavas dabas lieguma pelēkajās kāpās izveidoti 233 apļveida parauglaukumi (D= 3 m) vietās ar un …
Robusta binārā klasifikācija ar loģistisko regresiju
2019
Darbs veltīts loģistiskās regresijas izpētei, kas ir viena no populārākajām metodēm, risinot klasifikācijas uzdevumus. Kļūdas atkarīgajā mainīgajā var būtiski ietekmēt klasificēšanas veiktspēju. Darbā uzsvars likts uz robustu loģistiskās regresijas paplašinājumu, kas ir balstīts uz kļūdaino klašu ietveršanu modeļa apmācībā, lai modelis nezaudētu savu klasifikācijas veiktspēju. Modeļa apmācība noris līdzīgi kā loģistiskajā regresijā. Darbā aplūkota gan loģistiskā regresija, gan robustā loģistiskā regresija ar nobīdes parametriem. Abas metodes pielietotas praktiski programmā R Studio uz reāliem datiem. Darba mērķis ir pārbaudīt, kā abas metodes darbojās un salīdzināt sniegtos rezultātus.
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…
GLM-based automatic picking of waveforms
2011
Small RNA‐binding protein RapZ mediates cell envelope precursor sensing and signaling in Escherichia coli
2019
Abstract The RNA‐binding protein RapZ cooperates with small RNAs (sRNAs) GlmY and GlmZ to regulate the glmS mRNA in Escherichia coli. Enzyme GlmS synthesizes glucosamine‐6‐phosphate (GlcN6P), initiating cell envelope biosynthesis. GlmZ activates glmS expression by base‐pairing. When GlcN6P is ample, GlmZ is bound by RapZ and degraded through ribonuclease recruitment. Upon GlcN6P depletion, the decoy sRNA GlmY accumulates through a previously unknown mechanism and sequesters RapZ, suppressing GlmZ decay. This circuit ensures GlcN6P homeostasis and thereby envelope integrity. In this work, we identify RapZ as GlcN6P receptor. GlcN6P‐free RapZ stimulates phosphorylation of the two‐component sy…
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…