Search results for "Probability and Uncertainty"
showing 10 items of 578 documents
Managing hepatitis C in liver transplant patients with recurrent infection
2009
Tim Zimmermann1, Gerd Otto2, Marcus Schuchmann11Department of Internal Medicine, 2Transplantation Surgery, University of Mainz, GermanyAbstract: Hepatitis C virus (HCV) reinfection after liver transplantation (LT) and recurrent hepatitis C often lead to recurrent cirrhosis (RC). RC is one of the most frequent complications resulting in organ failure and early death after LT in HCV-positive patients with reported 5-year rates from 20% to 40%. As HCV-cirrhosis is one of the leading indications for LT, the therapeutic management is a central issue. To date, the best available therapy is a combination of pegylated interferon + ribavirin in patients with established recurrent hepatitis C proven …
The Integrated Nested Laplace Approximation for fitting Dirichlet regression models
2022
This paper introduces a Laplace approximation to Bayesian inference in Dirichlet regression models, which can be used to analyze a set of variables on a simplex exhibiting skewness and heteroscedasticity, without having to transform the data.These data, which mainly consist of proportions or percentages of disjoint categories, are widely known as compositional data and are common in areas such as ecology, geology, and psychology. We provide both the theoretical foundations and a description of how Laplace approximation can be implemented in the case of Dirichlet regression.The paper also introduces the package dirinla in the R-language that extends the RINLA package, which can not deal dire…
Covariate-informed latent interaction models: Addressing geographic & taxonomic bias in predicting bird-plant interactions
2023
Reductions in natural habitats urge that we better understand species' interconnection and how biological communities respond to environmental changes. However, ecological studies of species' interactions are limited by their geographic and taxonomic focus which can distort our understanding of interaction dynamics. We focus on bird-plant interactions that refer to situations of potential fruit consumption and seed dispersal. We develop an approach for predicting species' interactions that accounts for errors in the recorded interaction networks, addresses the geographic and taxonomic biases of existing studies, is based on latent factors to increase flexibility and borrow information acros…
Entry under uncertainty: Limit and most-favored-customer pricing
2015
Abstract In the absence of uncertainty, an incumbent that attempts to prevent entry of rival firms can have no incentive to offer a most-favored-customer (MFC) clause because it could lead to higher post-entry prices. Our analysis suggests that this is not necessarily the case under uncertainty. In the presence of uncertainty, the incumbent can set a limit price that affects the entry decision. Limit pricing involves a pre-entry price different from the static monopoly price, which leads to a signaling cost. We show that part of this cost can be distributed over several periods by means of consumer refunds from the MFC clause. If the discount factor is not very high, the incumbent adopts th…
The migrant crisis in the Mediterranean Sea: Empirical evidence on policy interventions
2021
Abstract This paper presents a novel set of empirical evidence to explore several hypotheses regarding the migrant crisis in the Mediterranean Sea. The political instability in transit countries, such as Libya, that made pre-existent repatriation policies ineffective, called for several search-and-rescue operations in the Mediterranean, which in turn have been wrongly accused of fostering illegal immigration and increasing deaths at sea. The empirical results show that the main determinants of the departures are several root causes at the departing African countries, underlining the importance of fighting human smuggling networks. The paper suggests a change in migration studies’ perspectiv…
Multivariate nonparametric tests in a randomized complete block design
2003
AbstractIn this paper multivariate extensions of the Friedman and Page tests for the comparison of several treatments are introduced. Related unadjusted and adjusted treatment effect estimates for the multivariate response variable are also found and their properties discussed. The test statistics and estimates are analogous to the traditional univariate methods. In test constructions, the univariate ranks are replaced by multivariate spatial ranks (J. Nonparam. Statist. 5 (1995) 201). Asymptotic theory is developed to provide approximations for the limiting distributions of the test statistics and estimates. Limiting efficiencies of the tests and treatment effect estimates are found in the…
Characters of relative p'-degree over normal subgroups
2013
Let Z be a normal subgroup of a finite group G , let ??Irr(Z) be an irreducible complex character of Z , and let p be a prime number. If p does not divide the integers ?(1)/?(1) for all ??Irr(G) lying over ? , then we prove that the Sylow p -subgroups of G/Z are abelian. This theorem, which generalizes the Gluck-Wolf Theorem to arbitrary finite groups, is one of the principal obstacles to proving the celebrated Brauer Height Zero Conjecture
Comparing Boosting and Bagging for Decision Trees of Rankings
2021
AbstractDecision tree learning is among the most popular and most traditional families of machine learning algorithms. While these techniques excel in being quite intuitive and interpretable, they also suffer from instability: small perturbations in the training data may result in big changes in the predictions. The so-called ensemble methods combine the output of multiple trees, which makes the decision more reliable and stable. They have been primarily applied to numeric prediction problems and to classification tasks. In the last years, some attempts to extend the ensemble methods to ordinal data can be found in the literature, but no concrete methodology has been provided for preference…
Who sent the e-mail?
2003
In mid October 2001, a number of lecturers at the University of Valencia received insulting, threatening and anonymous electronic mails. An investigation about this fact is only permitted under very restricted conditions, stipulated by the Spanish law of the Secrecy of Communications. Only one judicial authority is able to lift these restrictions and authorize information to be checked in order to obtain enough evidence to unveil who was responsible for the messages. The authors propose in this paper a study for quantifying the weight of certain evidence with a view to show to the judge that the relevance of the said weight would justify such a measure.