• Journal of Magnetics
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• 제3권3호
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• pp.86-88
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• 1998

A portable RF HTS SQUID-based susceptometer was used for small size magnetized sample testing in weak DC (up to 200A/m) and AC (up to 4 A/m) magnetic fields. The system resolution for the magnetic moment is of the order of $1.6{\times}10^{-10} A.m^2$. The measured DC susceptibility of a tested sample agrees well with the value obtained by using a commercial liquid helium susceptometer.

• Journal of Korea Trade
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• 제23권4호
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• pp.30-57
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• 2019

Purpose - This study analyzes the effect of internationalization represented as exporting on firm performance on the subject of SMEs operating in Masan Free Trade Zone which has shown poor performance recently despite its status as the oldest and largest free trade zone in Korea. We also analyze the effect of firm size on firm performance, and the moderating role of firm size in relation to internationalization and firm performance. Design/methodology - This study uses multiple regression models for unbalanced panel data as the empirical tools for the estimation of the effect that internationalization has on firm performance (ROA or ROS). Our sample consists of 91 manufacturing SMEs among all 110 companies located in Masan Free Trade Zone as of 2017. Findings - The degree of internationalization has a negative impact on firm performance. However, firm size turns out to have a positive effect and play a positive moderating role in the relation to internationalization and firm performance. This seems to be because most tenant companies operating in Masan Free Trade Zone are small firms whose costs of internationalization may exceed the benefits. Empirical results also show that longer CEO tenure has a greater negative effect on firm performance. Originality/value - The originality/value of this paper can be found in 3 aspects. First, we conducted an empirical analysis on the relationship between the internationalization and firm performance of SMEs in a specific region, namely, Masan Free Trade Zone. Second, while most previous studies focused on listed medium companies, most of the sample of this study are small and medium non-listed enterprises. Third, it is witnessed that firm size has a positive moderating effect on the relation between internationalization and firm performance.

• 한국산업보건학회지
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• 제32권1호
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• pp.21-30
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• 2022

Objectives: The purpose of this study is to suggest an optimal method by comparing the analysis methods of work environment measurement datasets including left-censored data where one or more measurements are below the limit of detection (LOD). Methods: A computer program was used to generate left-censored datasets for various combinations of censoring rate (1% to 90%) and sample size (30 to 300). For the analysis of the censored data, the simple substitution method (LOD/2), β-substitution method, maximum likelihood estimation (MLE) method, Bayesian method, and regression on order statistics (ROS)were all compared. Each method was used to estimate four parameters of the log-normal distribution: (1) geometric mean (GM), (2) geometric standard deviation (GSD), (3) 95th percentile (X95), and (4) arithmetic mean (AM) for the censored dataset. The performance of each method was evaluated using relative bias and relative root mean squared error (rMSE). Results: In the case of the largest sample size (n=300), when the censoring rate was less than 40%, the relative bias and rMSE were small for all five methods. When the censoring rate was large (70%, 90%), the simple substitution method was inappropriate because the relative bias was the largest, regardless of the sample size. When the sample size was small and the censoring rate was large, the Bayesian method, the β-substitution method, and the MLE method showed the smallest relative bias. Conclusions: The accuracy and precision of all methods tended to increase as the sample size was larger and the censoring rate was smaller. The simple substitution method was inappropriate when the censoring rate was high, and the β-substitution method, MLE method, and Bayesian method can be widely applied.

• 대한산업공학회지
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• 제42권4호
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• pp.256-262
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• 2016

The Weibull is widely used in reliability analysis, and several studies have attempted to improve estimation of the distribution's parameters. least squares estimation (LSE) or Maximum likelihood estimation (MLE) are often used to estimate distribution parameters. However, it has been proven that Bayesian methods are more suitable for small sample sizes than LSE and MLE. In this work, the Weibull parameter estimation accuracy of LSE, MLE, and Bayesian method are compared for sample sets with 3 to 30 data points. The Bayesian method was most accurate for sample sizes under 25, and the accuracy of the Bayesian method was similar to LSE and MLE as the sample size increased.

• 응용통계연구
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• 제27권1호
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• pp.1-11
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• 2014

세 개 이상의 집단에 대한 생존분포의 비교를 위해 가중 로그순위 검정법(Weighted Logrank test)과 그의 특별한 경우인 로그순위 검정법(Logrank test)이 널리 쓰인다. 그러나 이 방법은 근사적인 분포를 이용한 방법이므로 표본 크기가 작은 경우에는 유효하지 못할 수 있으며, 각 집단의 중도절단 분포가 동일하다는 가정 또한 충족되어야 하기 때문에 이 가정이 충족되지 못할 경우에도 검정법의 유효성을 장담할 수 없다. 표본 크기가 작은 경우에 대한 대안으로, 분포에 대한 가정이 없이 관찰된 자료만으로 검정통계량의 분포를 추정하고 그 분포를 이용해 검정하는 순열 검정법(Permutation test)이 제안되었으나, 순열 검정법 또한 각 집단의 중도절단 분포가 동일하다는 가정이 충족되어야 한다. 따라서 순열 검정법을 향상시킨 순열-대치 검정법(Permutation-Imputation test)이 대안이 될 수 있는데, 이는 대치 단계(Imputation step)에서 귀무가설 하에서의 생존확률이 집단에 의존하지 않도록 자료를 조정한 후 순열 검정 단계(Permutation step)를 통해 검정하는 방법이다. 본 논문에서는 근사적 방법, 순열 검정법, 순열-대치 검정법을 로그순위 검정법과 가중 로그순위 검정법의 한 형태인 Prentice-Wilcoxon 검정법에 적용해 각 검정법의 유효성과 검정력을 비교하였다.

• Journal of the Korean Data and Information Science Society
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• 제13권2호
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• pp.39-44
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• 2002

We compare MISE of the MLE, UMVUE, invariantly optimal estimator and Jacknife estimator for the reliability function of the Weibull distribution when the sample size is small.

• Journal of the Korean Statistical Society
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• 제16권2호
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• pp.113-116
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• 1987

The role of randomization is examined with regard to the Simpson's paradox. When the sample size n is large, it is known that the randomization is powerful in preventing the Simpson's paradox. In the present study, the question is whether is performs well for small n.

• Journal of the Korean Data and Information Science Society
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• 제11권2호
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• pp.303-312
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• 2000

We compare the MLE, UMVUE and Jackknife Estimators for the reliability function of the weibull distribution when the sample size is small.

• Journal of the Korean Data and Information Science Society
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• 제7권2호
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• pp.189-201
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• 1996

In this paper, we study the saddlepoint approximations for the ratio of independent random variables. In Section 2, we derive the saddlepoint approximation to the density. And in Section 3, we derive two approximation formulae for the tail probability, one by following Daniels'(1987) method and the other by following Lugannani and Rice's (1980). In Section 4, we represent some numerical examples which show that the errors are small even for small sample size.

• Journal of the Korean Data and Information Science Society
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• 제10권2호
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• pp.415-428
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• 1999

In this paper, we study the saddlepoint approximations for the ratio of two independent sequences of random variables. In Section 2, we review the saddlepoint approximation to the probability density function. In section 3, we derive an saddlepoint approximation formular for the tail probability by following Daniels'(1987) method. In Section 4, we represent a numerical example which shows that the errors are small even for small sample size.