122 research outputs found
Multivariate Skew-t Distributions in Econometrics and Environmetrics
No full textThis dissertation is composed of three articles describing novel approaches for
analysis and modeling using multivariate skew-normal and skew-t distributions in
econometrics and environmetrics.
In the first article we introduce the Heckman selection-t model. Sample selection
arises often as a result of the partial observability of the outcome of interest in
a study. In the presence of sample selection, the observed data do not represent a
random sample from the population, even after controlling for explanatory variables.
Heckman introduced a sample-selection model to analyze such data and proposed a
full maximum likelihood estimation method under the assumption of normality. The
method was criticized in the literature because of its sensitivity to the normality assumption.
In practice, data, such as income or expenditure data, often violate the
normality assumption because of heavier tails. We first establish a new link between
sample-selection models and recently studied families of extended skew-elliptical distributions.
This then allows us to introduce a selection-t model, which models the
error distribution using a Student���s t distribution. We study its properties and investigate
the finite-sample performance of the maximum likelihood estimators for
this model. We compare the performance of the selection-t model to the Heckman
selection model and apply it to analyze ambulatory expenditures.
In the second article we introduce a family of multivariate log-skew-elliptical distributions,
extending the list of multivariate distributions with positive support. We
investigate their probabilistic properties such as stochastic representations, marginal
and conditional distributions, and existence of moments, as well as inferential properties.
We demonstrate, for example, that as for the log-t distribution, the positive
moments of the log-skew-t distribution do not exist. Our emphasis is on two special
cases, the log-skew-normal and log-skew-t distributions, which we use to analyze U.S.
precipitation data.
Many commonly used statistical methods assume that data are normally distributed.
This assumption is often violated in practice which prompted the development
of more flexible distributions. In the third article we describe two such multivariate
distributions, the skew-normal and the skew-t, and present commands for
fitting univariate and multivariate skew-normal and skew-t regressions in the statistical
software package Stata
Estimating variance components in Stata
No full textThis article gives a brief overview of the popular methods for estimating variance components in linear models and describes several ways to obtain such estimates in Stata for various experimental designs. The article’s emphasis is on using xtmixed to estimate variance components. Prior to Stata 9, loneway could be used to estimate variance components for one-way random-effects models. For other experimental designs, variance components could be computed manually using saved results after anova. The latter approach is viable but requires tedious computations for complicated experimental designs. Instead, as of Stata 9, variance components are easily obtained by using xtmixed
Analysis and suggestion of a functional corporate identity for a company providing design and printing "Vsigns".
No full textThis bachelor thesis deals with the analysis and suggestion of a new functional corporate identity for the company "Vsigns", which provides design and printing and offers its experience in the production of custom advertising for a wide range of companies. The company "Vsigns" wants to cooperate as much as possible with large companies, and therefore the author decided to create a new visual identity not only for the company, but also on their social networks. The aim of this bachelor thesis is to improve the promotion of the company in the market and unify the visual presentation of the company. The work consists of two parts: theoretical and practical. In the theoretical part, attention is paid to the definitions needed to build a new corporate identity. This section also discusses the tools that can be used to analyze target groups and markets, marketing research and design a functioning strategic planning. The practical part is devoted to defining the problems, mission, vision and goals of the company, the analysis of the company is performed, and a new visual presentation of the company is proposed, including a new unified style for the social networks of the company "Vsigns".Tato bakalářská práce se zabývá analýzou a návrhem nové funkční firemní identity pro firmu „Vsigns“, která poskytuje design a tisk a nabízí své zkušenosti s výrobou zakázkové reklamy pro širokou škálu společností. Firma „Vsigns“ chce co nejvíce spolupracovat s velkými firmami, a proto se autorka rozhodla udělat novou vizuální identitu nejen na pobočce, ale i na sociálních sítích. Cílem této bakalářské práce je zlepšit propagaci firmy na trhu a sjednotit vizuální prezentaci společnosti. Práce se skládá ze dvou částí: teoretická a praktická. V teoretické části se pozornost věnuje definicím potřebným pro vybudování nové firemní identity. V této části se rozebírají i nástroje, pomocí kterých se dá provést analýza cílových skupin a trhu, marketingový výzkum a navrhnout fungující strategické plánování. Praktická část je věnována definování problémů, mise, vize a cíle společnosti, provádí se analýza podniku, a je navržena nová vizuální prezentace společnosti včetně nového jednotného stylu pro sociální sítě firmy „Vsigns“
Влияние долгосрочной дивидендной политики на доходность и волатильность акций
No full textGoal: determine if there is empirical relationship between dividend policy and stock returns and volatility
Objectives: provide an overview of theories describing different aspects of dividend policy that provide basis for results interpretation, formulate dividend policy analysis framework, study US public companies to find dividend policy effect on stock price and volatility.
Key results: Using a framework that combines two quantifiable characteristics of common stock dividend policy: payout ratio and Speed of Adjustment of dividends author constructed and compared portfolios of companies with different dividend policy characteristics. Main findings are: higher payout ratios are on average associated with lower returns, SOA does not affect returns, more volatile stocks tend to have lower payout ratios, stocks with higher SOA are more risky. Managers may use dividend policy to affect stock price and volatility.Цель: определить, есть ли эмпирическая связь между дивидендной политикой и доходностью и волатильностью акций.
Задачи: подготовить обзор теорий, описывающих различные аспекты дивидендной политики, которые могут быть использованы для интерпретации результатов, сформулировать основные характеристики дивидендной политики, провести анализ данных по публичным компаниям США, чтобы определить влияние дивидендной политики на доходность и волатильность акций.
Основные результаты: Используя два показателя, характеризующих дивидендную политику, коэффициент дивидендных выплат и скорость приспособления дивидендов, были сформированы портфели компаний с различными значениями характеристик дивидендной политики. Основные выводы: акции с более высоким коэффициентом дивидендных выплат в среднем имеют меньшую доходность, скорость приспособления дивидендов не влияет доходность, более волатильные акции, как правило характеризуются более низкими коэффициентами дивидендных выплат, акции с высокой скоростью приспособления дивидендов являются более рискованными. Менеджеры могут использовать дивидендную политику, чтобы влиять на доходность и волатильность акций
Multivariate log-skew-elliptical distributions with applications to precipitation data
No full textWe introduce a family of multivariate log-skew-elliptical distributions, extending the list of multivariate distributions with positive support. We investigate their probabilistic properties such as stochastic representations, marginal and conditional distributions, and existence of moments, as well as inferential properties. We demonstrate, for example, that as for the log-t distribution, the positive moments of the log-skew-t distribution do not exist. Our emphasis is on two special cases, the log-skew-normal and log-skew-t distributions, which we use to analyze US national (univariate) and regional (multivariate) monthly precipitation data. © 2009 John Wiley & Sons, Ltd.Genton’s research was supported in part by NSF grants DMS-0504896, CMG ATM-0620624, and by AwardNo. KUS-C1-016-04, made by King Abdullah University of Science and Technology (KAUST). The authors thankReinaldo B. Arellano-Valle, Kenneth P. Bowman, and a referee for their helpful comments and suggestions. The mapof US climatic regions was made available by the National Oceanic and Atmospheric Administration/Departmentof Commerc
A Heckman Selection- t Model
No full textSample selection arises often in practice as a result of the partial observability of the outcome of interest in a study. In the presence of sample selection, the observed data do not represent a random sample from the population, even after controlling for explanatory variables. That is, data are missing not at random. Thus, standard analysis using only complete cases will lead to biased results. Heckman introduced a sample selection model to analyze such data and proposed a full maximum likelihood estimation method under the assumption of normality. The method was criticized in the literature because of its sensitivity to the normality assumption. In practice, data, such as income or expenditure data, often violate the normality assumption because of heavier tails. We first establish a new link between sample selection models and recently studied families of extended skew-elliptical distributions. Then, this allows us to introduce a selection-t (SLt) model, which models the error distribution using a Student's t distribution. We study its properties and investigate the finite-sample performance of the maximum likelihood estimators for this model. We compare the performance of the SLt model to the conventional Heckman selection-normal (SLN) model and apply it to analyze ambulatory expenditures. Unlike the SLNmodel, our analysis using the SLt model provides statistical evidence for the existence of sample selection bias in these data. We also investigate the performance of the test for sample selection bias based on the SLt model and compare it with the performances of several tests used with the SLN model. Our findings indicate that the latter tests can be misleading in the presence of heavy-tailed data. © 2012 American Statistical Association.The authors thank the editor, the associate editor, and two referees for a careful review of the manuscript and valuable suggestions. The authors also thank Adelchi Azzalini and Reinaldo B. Arellano-Valle for helpful comments on an earlier version of the article, and David Drukker for useful discussions about selection models. Genton's research was partially supported by the National Science Foundation (NSF) grant DMS-1007504 and by award number KUS-C1-016-04 made by King Abdullah University of Science and Technology (KAUST)
A suite of commands for fitting the skew-normal and skew-t models
No full textNonnormal data arise often in practice, prompting the development of flexible distributions for modeling such situations. In this article, we describe two multivariate distributions, the skew-normal and the skew-t, which can be used to model skewed and heavy-tailed continuous data. We then discuss some inferential issues that can arise when fitting these distributions to real data. We also consider the use of these distributions in a regression setting for more flexible parametric modeling of the conditional distribution given other predictors. We present commands for fitting univariate and multivariate skew-normal and skew-t regressions in Stata (skewnreg, skewtreg, mskewnreg, and mskewtreg) as well as some postestimation features (predict and skewrplot). We also demonstrate the use of the commands for the analysis of the famous Australian Institute of Sport data and U.S. precipitation data. Copyright 2010 by StataCorp LP.skewnreg, skewtreg, mskewnreg, mskewtreg, skewrplot, predict, distribution, heavy tails, nonnormal, precipitation, regression, skewness, skew- normal, skew-t
Relationship between NT-proBNP and the ejection fraction during intensive care variety in polytrauma patients with concomitant cardiac disorder
No full textLutska Svitlana V., Volkova Yulia V., Mykhnevych Kostiantyn G. Relationship between NT-proBNP and the ejection fraction during intensive care variety in polytrauma patients with concomitant cardiac disorder. Journal of Education, Health and Sport. 2021;11(10):88-101. eISSN 2391-8306. DOI http://dx.doi.org/10.12775/JEHS.2021.11.10.008
https://apcz.umk.pl/JEHS/article/view/JEHS.2021.11.10.008
https://zenodo.org/record/5579233
The journal has had 5 points in Ministry of Science and Higher Education parametric evaluation. § 8. 2) and § 12. 1. 2) 22.02.2019.
© The Authors 2021;
This article is published with open access at Licensee Open Journal Systems of Nicolaus Copernicus University in Torun, Poland
Open Access. This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium,
provided the original author (s) and source are credited. This is an open access article licensed under the terms of the Creative Commons Attribution Non commercial license Share alike.
(http://creativecommons.org/licenses/by-nc-sa/4.0/) which permits unrestricted, non commercial use, distribution and reproduction in any medium, provided the work is properly cited.
The authors declare that there is no conflict of interests regarding the publication of this paper.
Received: 30.09.2021. Revised: 12.10.2021. Accepted: 19.10.2021.
RELATIONSHIP BETWEEN NT-proBNP AND THE EJECTION FRACTION DURING INTENSIVE CARE VARIETY IN POLYTRAUMA PATIENTS WITH CONCOMITANT CARDIAC DISORDER
Svitlana V. Lutska, Yulia V. Volkova, Kostiantyn G. Mykhnevych
Kharkiv National Medical University, Kharkiv, Ukraine
Svitlana Vitaliivna Lutska; [email protected]
ORCID ID https://orcid.org/0000-0002-0633-9801
Postgraduate student, Kharkiv National Medical University, Department of Emergency Medicine, Anesthesiology and Intensive Care, Kharkiv, Ukraine.
Yuliya Viktorivna Volkova; [email protected]
ORCID ID: https://orcid.org/0000-0001-8000-5802
Doctor of Medical Sciences, Professor, Kharkiv National Medical University, Department of Emergency Medicine, Anesthesiology and Intensive Care, Kharkiv, Ukraine.
Kostiantyn Georgijovych Mykhnevych; [email protected]
ORCID ID: https://orcid.org/0000-0002-6135-7121
Doctor of Medical Sciences, Professor, Kharkiv National Medical University, Department of Emergency Medicine, Anesthesiology and Intensive Care, Kharkiv, Ukraine.
Abstract
The aim. To research the impact of chronic heart failure within different origin in case of polytrauma without myocardial injury.
Materials and methods. The study the analyzed results of intensive care in 95 patients with polytrauma between the ages of 25 and 83. All patients were divided into 3 groups. Group C included 29 patients without chronic heart failure (CHF), groups C - 33 patients with CHF, the presence which was confirmed by the level of NT-proBNP more than 100 pg/ml, group E - 33 patients with CHF. Patients of groups K and C received standard intensive care, patients of group E additionally received ethylmethylhydroxypyridine succinate (EMGPS). The study was carried out at three stages: during admission to the hospital, at the 3rd and 7th day. During admission, the level of Th I was determined in order to exclude traumatic or other acute myocardial lesions. At a concentration of Tn I more than 0.3 ng/ml, patients were not included in the study.
Results. During admission, NT-proBNP level in all K-group patients did not exceed 87 pg/ml throughout the study. The ejection fraction (EF) was averaged 53,7±3,4%. The NT-proBNP dynamics were as followed by 116.4±7.0, 114.4±7.4, 109.1±8.5 pg/ml. The NT-proBNP and EF correlation coefficient was according to the stages -0.84±0.06, -0.74±0.08, -0.68±0.09. The value of the EF at hospitalization in group C was 47.9±4.7%, on the 3rd day 52.2±5.2% (p < 0.001), and by 7th - until 56.8±6.9% (p < 0.001). NT-proBNP level in E patients: 119.2±10.8, 113.2±8.1 (p= 0.02), 65.2±23.3 (p < 0.0001). At stage 1 and 2, a strong negative correlation effect was observed (-0.78±0.07 and -0.77±0.07, accordingly), at the 3 stage the communication disappeared (0.07±0.17). Within admission EF level was 47.5±6.9 %.
Conclusions. The level of NT-proBNP authentically reflects the relationship with chronic heart failure. There is also a strong correlation between NT-proBNP and EF. Therefore, it is clear from the study that NT-proBNP has not undergone changes in group K (87 pg/ml), in contrast to patients of groups C (116.4±7.0,114.4±7.4, 109.1±8.5 pg/ml) and E (119.2±10.8, 113.2±8.1 (p =0.02), 65.2±23.3 (p < 0.0001) who had concomitant disorder such as chronic heart failure.
Key words: polytrauma; heart failure; NT-proBNP; ejection fraction
Improved degrees of freedom for multivariate significance tests obtained from multiply imputed, small-sample data
No full textWe propose improvements to existing degrees of freedom used for significance testing of multivariate hypotheses in small samples when missing data are handled using multiple imputation. The improvements are for 1) tests based on unrestricted fractions of missing information and 2) tests based on equal fractions of missing information with M (p − 1) ≤ 4, where M is the number of imputations and p is the number of tested parameters. Using the mi command available as of Stata 11, we demonstrate via simulation that using these adjustments can result in a more sensible degrees of freedom (and hence closer-to-nominal rejection rates) than existing degrees of freedom. Copyright 2009 by StataCorp LP.multiple imputation, degrees of freedom, sample, missing, testing, multivariate
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