• The Korean Journal of Applied Statistics
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• v.21 no.6
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• pp.923-932
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• 2008

We are likely to face complex multivariate data which can be characterized by having a non-trivial correlation structure. For instance, omitted covariates may simultaneously affect more than one count in clustered data; hence, the modeling of the correlation structure is important for the efficiency of the estimator and the computation of correct standard errors, i.e., valid inference. A standard way to insert dependence among counts is to assume that they share some common unobservable variables. For this assumption, we fitted correlated random effect models considering multilevel model. Estimation was carried out by adopting the semiparametric approach through a finite mixture EM algorithm without parametric assumptions upon the random coefficients distribution.

• Journal of Embryo Transfer
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• v.31 no.3
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• pp.243-247
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• 2016

Growth traits, such as body weight, directly influence productivity and economic efficiency in the swine industry. In this study, we estimate heritability for body weight traits usinginformation from pedigree and genome-wide single nucleotide polymorphism (SNP) chip data. Four body weight phenotypes were measured in 1,105 $F_2$ progeny from an intercross between Landrace and Jeju native black pigs. All experimental animals were subjected to genotypic analysis using PorcineSNP60K BeadChip platform, and 39,992 autosomal SNP markers filtered by quality control criteria were used to construct genomic relationship matrix for heritability estimation. Restricted maximum likelihood estimates of heritability were obtained using both genomic- and pedigree- relationship matrix in a linear mixed model. The heritability estimates using SNP information were smaller (0.36-0.55) than those which were estimated using pedigree information (0.62-0.97). To investigate effect of common environment, such as maternal effect, on heritability estimation, we included maternal effect as an additional random effect term in the linear mixed model analysis. We detected substantial proportions of phenotypic variance components were explained by maternal effect. And the heritability estimates using both pedigree and SNP information were decreased. Therefore, heritability estimates must be interpreted cautiously when there are obvious common environmental variance components.

• Journal of Korean Society of Transportation
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• v.32 no.6
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• pp.662-674
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• 2014

In this study, accident frequency prediction models were constructed by collecting variables such as geometric structures, safety facilities, traffic volume and weather conditions, land use, highway design-satisfaction criteria along 780km (4,372 sections) of 4 lane-highways over 8 areas. As for models, a fixed parameter model and a random parameter model were employed. In the random parameter model, some influences were reversed as the range was expressed based on specific probability in the case of no fixed coefficients. In the fixed parameter model, the influences of independent variables on accident frequency were interpreted by using one coefficient, but in the random parameter model, more various interpretations were took place. In particular, curve radius, securement of shoulder lane, vertical grade design criteria satisfaction showed both positive and negative influence, according to specific probability. This means that there could be a reverse effect depending on the behavioral characteristics of drivers and the characteristics of highway sections. Rather, they influence the increase of accident frequency through the all sections.

• 한국사회정책
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• v.23 no.1
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• pp.95-123
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• 2016

As Korean society grows rapidly older, a systematic analysis of the determinants of labor supply behavior among the elderly becomes a prerequisite for designing more effective senior employment policies and income security regime for the elderly. Literatures review shows that a majority of previous researches have been ignoring the problem of "endogenous predictor" especially when it comes to the estimation of the effects of the two key variables, education and non-labor income, on labor supply decisions among older people. They have failed to take into consideration the unobserved heterogeneities which might affect both labor supply decisions of the elderly and their levels of education and non-labor income, which means, according to some econometric literatures, that the estimated coefficients of the two predictors can be inconsistent. The paper tries to redress the endogeneity problem by employing a panel logit model with data from the 1st. to 4th. wave of the KLoSA(Korean Longitudinal Survey of Ageing) to estimate the effects of key predictors on the probability of getting jobs among older people(ages of 60 or older). Both a random effects and a fixed effects model reaffirms that non-labor income has a negative effect on the chances of being employed. And a random effects model shows that the effect of education is also negative, as has frequently been reported by previous studies. That means the effects of education and non-labor income on elderly employment remain negative after the effect of unobserved heterogeneities is controled for and the problem of endogenous predictors is redressed through an appropriate panel data analysis. These findings mean, in turn, that when Korean baby-boomers, who had acquired an unprecedentedly higher level of education and were expected to enjoy ever-larger amount of non-labor income than their preceding generations, retires in near future, their incentives to work will become much weaker and the lack of labor-force and the burden of financing increased public pension expenditure will become more troublesome. The paper concludes with recommending some policy initiatives helpful to solve these expected problems.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.2
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• pp.107-117
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• 2020

The research objective of the paper is to clarify the factors influencing system risks of listed companies in Vietnam, with a focus on clarifying the relationship and quantifying the impacts of ownership structure on systemic risk of listed companies. The data used in this study included financial statements and stock price data of listed companies on the Ho Chi Minh City Stock Exchange and Hanoi Stock Exchange of Vietnam stock market in the period from 2010 to 2017. The paper used the method of estimation in establising the regression models to choose among three models: Random Effect Model, Fixed Effect Model or Pooled OLS for regression using Stata statistical software. The research results showed that state ownership and ownership by foreign investors were positively related to systemic risk, while ownership by domestic investors had a reverse relationship with systemic risk of listed companies in Vietnam. In addition, as a control variable, both company size and profitability had an effect on the systemic risk of listed companies in the research sample. Based on the research results, the authors interpreted some of the implications in order to minimize systemic risks in the operation of listed companies in Vietnam.

• The Journal of Asian Finance, Economics and Business
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• v.9 no.7
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• pp.231-237
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• 2022

Intellectual Capital, a valuable intangible organizational asset, is primarily linked to a company's financial performance and is divided into three categories: human, structural, and relational capital. This paper investigates the impact of intellectual capital on the financial performance of selected Pakistani companies in the Information and Communication sector, as this sector is heavily reliant on intellectual capital. The data for 11 firms was gathered from the State Bank's Financial Statements Analysis of Companies Listed on the Pakistan Stock Exchange from 2015 to 2020. Pulić's (2004) Value Added Intellectual Coefficient (VAICTM) has been used to assess a company's IC efficiency. VAIC^TM and its components, the efficiency of intellectual capital, and the efficiency of capital employed are calculated. Financial performance is measured through return on assets, return on capital employed, and asset turnover ratio. Multiple regression, fixed-effect, and random-effect Panel Data estimation are used in the empirical study. The findings suggest that intellectual capital efficiency has a large impact on major profitability metrics, but little effect on company productivity. It can be inferred from the results that the companies must invest in advanced technology, the latest machinery, and well-equipped offices to improve financial performance and productivity and gain a competitive advantage.

• Proceedings of the Korean Society of Computational and Applied Mathematics Conference
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• 2003.09a
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• pp.14-14
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• 2003

Given a sequence ｛ $X_{n}$｝ of independent and identically distributed random variables with F, a sequential procedure for the p-th quantile ξ$_{P}$= $F^{-1}$ (P), 0$\beta$-protection. Some asymptotic properties for the proposed procedure and of an involved stopping time are proved: asymptotic consistency, asymptotic efficiency and asymptotic normality. From one of the results an effect of smoothing based on kernel functions is discussed. The results are also extended to the contaminated case.e.e.

• Structural Engineering and Mechanics
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• v.61 no.2
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• pp.183-192
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• 2017

Seismic pounding between adjacent buildings with inadequate separation and different dynamic characteristics can cause severe damage to the colliding buildings. Efficient estimation of the maximum pounding force is required to control the extent of damage in adjacent structures or develop an appropriate mitigation method. In this paper, an analytical approach on the basis of statistical relations is presented for approximate computation of extreme value of pounding force between two adjacent structures with equal or unequal heights subjected to stationary and non-stationary excitations. The nonlinearity of adjacent structures is considered using Bouc-Wen model of hysteresis and the pounding effect is simulated by applying the nonlinear viscoelastic model. It is shown that the proposed approach can significantly save computational costs by obviating the need for performing dynamic analysis. To assess the reliability and accuracy of the proposed approach, the results are compared with those obtained from nonlinear dynamic analysis.

• Journal of the Korean Data and Information Science Society
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• v.18 no.2
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• pp.535-541
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• 2007

The Non-homogeneous Poisson process is probably the most popular model since it can model systems that are deteriorating or improving. The renewal process is a model that is often used to describe the random occurrence of events in time. But both these models are based on too restrictive assumptions on the effect of the repair action. The Modulated Power Law Process is a suitable model for describing the failure pattern of repairable systems when both renewal-type behavior and time trend are present. In this paper we propose maximum likelihood estimation of the next failure time after the system has experienced some failures, that is, Mean Time Between Failure for the MPLP model.

• Proceedings of the KIEE Conference
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• 1999.07f
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• pp.2499-2501
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• 1999

Most of sensorless algorithm are based on motor equations where it is necessary to find the phase voltage and current. However, measurement error and environmental noise deteriorate the accuracy of speed estimation of PMSM. This paper investigates speed sensorless control of PMSM for noise rejection in harsh environment. The proposed algorithm is based on the interaction between electrical parameter and random noise. The evolution strategy is used for minimizing the noise effect. The proposed algorithm is verified through simulation and experiment.