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متن کامل


نشریه: 

ژنتیک نوین

اطلاعات دوره: 
  • سال: 

    1391
  • دوره: 

    7
  • شماره: 

    2 (پیاپی 29)
  • صفحات: 

    105-114
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    1266
  • دانلود: 

    554
چکیده: 

لطفا برای مشاهده چکیده به متن کامل (PDF) مراجعه فرمایید.

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اطلاعات دوره: 
  • سال: 

    1391
  • دوره: 

    5
  • شماره: 

    15
  • صفحات: 

    59-67
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    1832
  • دانلود: 

    690
چکیده: 

یکی از شیوه های تجزیه و تحلیل داده های مالی و بررسی چگونگی تغییرات آن ها در طی زمان معین در گذشته و پیش بینی چگونگی رخداد آن ها در آینده استفاده از مدل های سری های زمانی است.در مباحث مالی به دلیل نا هم واریانس بودن مشاهدات موجود، نمی توان از مدل های سری های زمانی کلاسیک استفاده کرد. در این حالت، یکی از مدل های متداول، مدل های نوع گارچ(GARCH) است که نشان دهنده رده وسیعی از مدل های اقتصادسنجی ناهم واریانس هستند. این مدل ها اولین بار توسط بولرسلو در سال 1986 معرفی شدند. مدل های سری های زمانی مانند مدل های رگرسیونی خطای تصادفی دارند. مدل های گارچ نیز از این امر مستثنی نیستند و این خطاهای تصادفی توزیع مشخصی دارند.به دلیل این که در مدل های گارچ تغییرپذیری مستقیما قابل رویت نیست، به منظور برآورد پارامترهای موجود در این مدل ها از روش های مدل گزینی بیزی استفاده می کنند. برای این منظور، ابتدا توزیع های پیشینی را روی این پارامترها در نظر می گیرند که توزیع پسین حاصل از آن انتگرال پذیر باشد. سپس توزیع پسین پارامترها را با استفاده از روش های محاسباتی زنجیر مارکوفی مونت کارلو ، مانند نمونه گیری گیبس و الگوریتم متروپولیس- هستینگ تقریب می زنند. اگر انتگرال موجود در مخرج کسر توزیع پسین قابل محاسبه نباشد، آن گاه از روی نمونه های حاصل از توزیع پسین، درستنمایی مدل را با به کار گرفتن روش های مستقیم مدل گزینی بیزی شامل: برآوردگر میانگین همساز، برآوردگر نقاط مهم معکوس و نمونه گیری بریج برآورد می کنند. یک روش غیرمستقیم برای برآورد درستنمایی مدل، استفاده از خروجی نمونه گیری گیبس است که به برآوردگر کاندید چیب معروف است. برای بهبود این روش، با استفاده از خروجی الگوریتم MH، برای درستنمایی می توان برآوردی به دست آورد. هم چنین روش MCMC پرشی برگشت پذیر برای نمونه های تولید شده از توزیع پسین توام بر اساس روش MH استاندارد استفاده می شود.

شاخص‌های تعامل:   مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources

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نویسندگان: 

Ghazanfari Azadeh | Fayyaz Movaghar Afshin

اطلاعات دوره: 
  • سال: 

    2024
  • دوره: 

    12
  • شماره: 

    4
  • صفحات: 

    281-290
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    6
  • دانلود: 

    0
چکیده: 

Background and Purpose: Genomic Selection is used to select candidates for breeding programs for organisms. In this study, we use the Bayesian Model averaging (BMA) method for genomic Selection by considering the skewed error distributions. Materials and Methods: In this study, we apply the BMA method to linear regression Models with skew-normal and skew-t distributions to determine the best subset of predictors. Occam’s window and Markov-Chain Monte Carlo Model composition (MC3) were used to determine the best Model and its uncertainty. The Rice SNP-seek database was used to obtain real data, which included 152 single nucleotide polymorphisms (SNPs) with 6 phenotypes. Results: Numerical studies on simulated and real data showed that, although Occam’s window ran faster than the MC3 method, the latter method suggested better linear Models for the data with both skew-normal and skew-t error distributions. Conclusion: The MC3 method performs better than Occam’s window in identifying the linear Models with greater accuracy when dealing with skewed error distributions.

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مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
نویسندگان: 

MOKHTARI GHASEM | Aghagoli Fatemeh

اطلاعات دوره: 
  • سال: 

    2020
  • دوره: 

    13
  • شماره: 

    2
  • صفحات: 

    197-219
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    142
  • دانلود: 

    0
چکیده: 

Risk identification, impact assessment, and response planning constitute three building blocks of project risk management. Correspondingly, three types of interactions could be envisioned between risks, between impacts of several risks on a portfolio component, and between several responses. While the interdependency of risks is a well-recognized issue, the other two types of interactions remain unacknowledged in the risk response planning literature. This research suggests a Bayesian belief network for Modeling portfolio risks, their impacts, and responses. There are three kinds of nodes in this network: nodes representing portfolio risks, nodes corresponding to risk impacts on each objective of each portfolio component, and nodes showing response actions. The problem is to decide which responses are to be selected. For this purpose, an optimization Model is proposed that minimizes the sum of both residual risk effects on portfolio component objectives and response implementation costs. Subsequently, a genetic algorithm is introduced to solve the Model. A simple portfolio instance is also provided to illustrate the proposed Model.

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بازدید 142

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نویسندگان: 

WOLFE P.J. | GODSILL S.J. | NG W.J.

اطلاعات دوره: 
  • سال: 

    2004
  • دوره: 

    66
  • شماره: 

    3
  • صفحات: 

    575-589
تعامل: 
  • استنادات: 

    1
  • بازدید: 

    195
  • دانلود: 

    0
کلیدواژه: 
چکیده: 

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بازدید 195

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نویسندگان: 

Naghizadeh Sima

اطلاعات دوره: 
  • سال: 

    2022
  • دوره: 

    1
  • شماره: 

    1
  • صفحات: 

    171-188
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    24
  • دانلود: 

    0
چکیده: 

The Bayesian variable Selection analysis is widely used as a new methodology in air quality control trials and generalized linear Models. One of the important and, of course, controversial topics in this area is Selection of prior distribution of unknown Model parameters. The aim of this study is presenting a substitution for mixture of priors which besides preservation of benefits and computational efficiencies obviate the available paradoxes and contradictions. In this research we pay attention to two points of view,empirical and fully Bayesian. Especially, a mixture of priors and its theoretical characteristics is introduced. Finally, the proposed Model is illustrated with a real example.

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مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
نویسندگان: 

Ormoz Ehsan | Eskandari Farzad

اطلاعات دوره: 
  • سال: 

    2024
  • دوره: 

    3
  • شماره: 

    2
  • صفحات: 

    15-34
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    7
  • دانلود: 

    0
چکیده: 

This paper introduces a novel semiparametric Bayesian approach for bivariate meta-regression. The method extends traditional binomial Models to trinomial distributions, accounting for positive, neutral, and negative treatment effects. Using a conditional Dirichlet process, we develop a Model to compare treatment and control groups across multiple clinical centers. This approach addresses the challenges posed by confounding factors in such studies. The primary objective is to assess treatment efficacy by Modeling response outcomes as trinomial distributions. We employ Gibbs sampling and the Metropolis-Hastings algorithm for posterior computation. These methods generate estimates of treatment effects while incorporating auxiliary variables that may influence outcomes. Simulations across various scenarios demonstrate the Model’s effectiveness. We also establish credible intervals to evaluate hypotheses related to treatment effects. Furthermore, we apply the methodology to real-world data on economic activity in Iran from 2009 to 2021. This application highlights the practical utility of our approach in meta-analytic contexts. Our research contributes to the growing body of literature on Bayesian methods in meta-analysis. It provides valuable insights for improving clinical study evaluations.

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نویسندگان: 

اطلاعات دوره: 
  • سال: 

    2021
  • دوره: 

    242
  • شماره: 

    -
  • صفحات: 

    108296-108296
تعامل: 
  • استنادات: 

    1
  • بازدید: 

    29
  • دانلود: 

    0
کلیدواژه: 
چکیده: 

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بازدید 29

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اطلاعات دوره: 
  • سال: 

    2019
  • دوره: 

    10
  • شماره: 

    1
  • صفحات: 

    3-12
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    124
  • دانلود: 

    0
چکیده: 

Introduction: The world prevalence of type 2 diabetes and its related increment mortality rate which needs high controls cost has attracted high scientific attention. Early detection of individuals who face this disease more than the others can prevent getting sick or at least reduce the disease consequences on public health. Regarding the costs and limitations of diagnostic tests, a statistical Model is presented that helps predict the time of diabetes incidence and determines its risk factors. Furthermore, this Model determines the significant predictor variables on response and considers them as Model equation parameters. Materials and Methods: In this study, 803 pre-diabetic women in the age range of more than 20 years were selected from Tehran lipid and glucose study (TLGS) to examine the predictor variables on time of diabetes incidence. They were entered into the study in the phases 1 and 2 and were followed up to the phase 4. The predictor variables Selection was performed using the Stepwise Model (SM) and the Bayesian Model Averaging (BMA). Then, the predictive discrimination was used to compare the results of both Models. The Log-rank test was performed and the Kaplan-Meier Curve was plotted. The statistical analyses were performed using R software (version 3. 1. 3). Results: The Backward Stepwise Model (BSM), the Forward Stepwise Model (FSM) and the BMA have used 9, 10 and 6 variables, respectively. Although the BMA selected predictor variables number is much lower than the SM, the prediction ability remains nearly constant. Conclusions: The BMA has averaged on the supported Models using dataset. This Model has shown nearly constant accuracy despite the Selection of lower predictor variables number in comparison to the SM.

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اطلاعات دوره: 
  • سال: 

    1401
  • دوره: 

    53
  • شماره: 

    4
  • صفحات: 

    245-254
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    138
  • دانلود: 

    20
چکیده: 

This study aimed to estimate the genetic parameters of body weight traits in Markhoz goats, using B-spline random regression Models. The data used in this study included 19549 records collected during 29 years (1992-2021) in Markhoz goat Breeding Research Station, located in Sanandaj, Iran. The Model used to analyze data included fixed effects (year of birth, sex, type of birth and age of dam) and random effects including direct additive genetic, maternal additive genetic, permanent environmental and maternal permanent environmental assuming homogeneous and heterogeneous residual variance during the time. Akaike (BIC) and Bayesian (BIC) information criteria were used to compare the Models and bspq.4.4.4.4 was selected as the best Model. The direct heritability values for birth, 3-month, 6-month, 9-month and 12-month weights were estimated to be 0.14, 0.16, 0.08, 0.28 and 0.26, respectively. Genetic correlation between body weights at birth and 3-month, birth and 6-month, birth and 9-month, birth and 12-month, 3-month and 6-month, 3-month and 9-month, 3-month and 12-month, 6-months and 9-month and 9-month and 12-month were 0.22, 0.38, 0.21, 0.56, -0.26, 0.30, 0.62, 0.86 and 0.77, respectively. The highest phenotypic correlation was between the weight of 9-month and 12-month (0.82) and the lowest correlation was between birth weight and 3-month and 6-month (0.12). The results showed that the 9-month weight is a good criterion for Selection in Markhoz goats.

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بازدید 138

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