• Journal of Korean Society of Transportation
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• v.23 no.5 s.83
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• pp.15-25
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• 2005

Using a stochastic cost frontier approach(SCFA), this paper annually estimates the efficiency and productivity with same data in the papers which analyze the efficiency and productivity using data envelopment analysis(DEA) to compare the results and suggest the political findings of raising the efficiency and productivity for three publicly-owned rail transit properties. the Seoul Subway Corporation (SSC), the Seoul Metropolitan Electrified Railways Sector of Korea National Railroad (SMESRS) and the Busan Urban Transit Authority (BUTA). The results show that the results of SCFA are higher than DEA for efficiency and lower for productivity in that DEA regards the stochastic error and measurement error as the inefficiency contrary to SFCA. But the political findings from these results appears to be similar as follows. First, the productivity of the three properties should be first improved by using existing technologies efficiently and then by introducing new ones. Second, the three properties should improve the technical efficiency through reducing input quantities to raise their efficiency. Finally, all the three components of the productivity such as productive efficiency change, technical change, and scale change should be considered to evaluate their productivity more correctly.

• Journal of Labour Economics
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• v.43 no.2
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• pp.109-133
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• 2020

This paper estimates a matching function in Korea by using the method of Borowczyk-Martins et al. (2013) in order to mitigate endogeneity problems. The endogeneity was controlled through the GMM estimation by approximating the unobserved matching efficiency with the ARMA(p,q) process. The monthly data from the Economically Active Population Survey and Labor Force Survey at Establishments from June 2009 to December 2019 were used for the estimation. The matching elasticity that indicates the elasticity of new hires with respect to vacancies was estimated to be 0.859. When excluding 2019 samples, which had a large number of direct jobs provided by the government, the matching elasticity was lowered to 0.755, but still higher than that of other countries.

• Survey Research
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• v.10 no.1
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• pp.141-154
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• 2009

With the current sampling scheme, the sampling variance is getting larger in producing smaller regional statistics than the designed area, The larger sample size can make the variance reduced but the efficiency of sample survey lower. The desired confidence level of sampling survey can be obtained using the current sample scheme with the same sample size and administrative data. In this paper, the number of the unemployed of 5 regions in Daejon are estimated using small area estimation methods and the CV values in each estimation method is calculated and compared for their estimation efficiency as empirical study. Jackknife method is proposed to estimate the MSE of synthetic estimator and composite estimator more accurately.

• Communications for Statistical Applications and Methods
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• v.4 no.1
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• pp.161-165
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• 1997

양적속성의 추정을 위한 확률화응답기법은 Greenberg et al.(1971)로부터 시작된다. 이후 새로운 방법에 대한 제시(Dalenius와 Vitale(1974)) 및 분포함수에 대한 추정(Duffy와 Waterton(1984))등이 연구되어 오고 있다. 본 연구에서는 2단계 확률화응답기법을 이용하여 양적속성을 추정하는 방법을 제시하고 이의 효율성 비교를 행해 보고자 한다.

• Journal of the Korean Data and Information Science Society
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• v.11 no.2
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• pp.295-302
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• 2000

We study the efficient method to estimate the parameters for the Weibull model with covariates which occupies an important position in survival analysis. A treatment period may be divided by the stages of treatments under the different treatment arams. The piecewise method is considered to obtain the estimators of the parameters by maximum likelihood method. We explore the real data to show that the piecewise is more efficient than the nonpiecewise to estimate the parameters.

• Proceedings of the Korean Statistical Society Conference
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• 2001.11a
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• pp.63-68
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• 2001

조사과정에서 필연적으로 발생하는 무응답을 보정하기 위해 보조정보를 사용한다. 이 때, 이용 가능한 보조정보의 차원이 크면, 계산과정에서 많은 시간이 소요되며 데이터를 다루기가 매우 어렵다. 또한 추정량의 분산이 보조정보의 차원에 의존하기 때문에 과소추정의 문제가 발생한다. 이러한 문제를 해결하기 위해 무응답 보정에서 적절한 보조정보의 선택 방법을 제안하였고, 이에 대한 효율성을 모의실험을 통해 살펴보았다.

• Proceedings of the Korean Society for Information Management Conference
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• 2000.08a
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• pp.113-118
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• 2000

색상에 의한 내용기반 이미지 검색 기법에 있어서 조명과 관찰자의 환경과 같은 주변 조건을 반영한 시지각 색상 모형은 사진 이미지 속에 나타나는 반사광과 그림자와 같은 영역의 색상 정보를 알 수 없는 것이라고 간주한다는 단점이 있다. 이 연구에서는 그와 같은 알 수 없는 정보를 빛의 방향에 의해 추정하여 검색 시스템의 효율을 향상시키려 하였으며, 검색 실험 결과 이러한 추정 작업과 검색 효율성 향상 사이에는 유의미한 관계가 존재하고 있는 것으로 결론지을 수 있었다.

• The Korean Journal of Applied Statistics
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• v.27 no.3
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• pp.397-406
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• 2014

The minimum density power divergence estimation has been a popular topic in the field of robust estimation for since Basu et al. (1988). The minimum density power divergence estimator has strong robustness properties with the little loss in asymptotic efficiency relative to the maximum likelihood estimator under model conditions. However, a limitation in applying this estimation method is the algebraic difficulty on an integral involved in an estimation function. This paper considers a minimum density power divergence estimation method with approximated divergence avoiding such difficulty. As an example, we consider the normal-exponential convolution model introduced by Bolstad (2004). The estimated divergence in this case is too complicated; consequently, a Laplace approximation is employed to obtain a manageable form. Simulations and an empirical study show that the minimum density power divergence estimators based on an approximated estimated divergence for the normal-exponential model perform adequately in terms of bias and efficiency.

• Communications for Statistical Applications and Methods
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• v.3 no.2
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• pp.43-51
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• 1996

균형일원변량모형에서 분산성분비율의 점추정에 관한 문제가 고려되어진다. 분산성분비율에 대한 점추정량의 종류를 살펴보고 추정량의 평균자승오차(MSE)를 서로 비교하여 본다. 분산성분비율에 대한 새로운 추정량이 제 안되며, 제안된 추정량을 사용하면 모의실험을 통하여 Das (1992)가 고려한 여러가지 형태의 추정량들보다 급내상관계수 ${\rho}$의 값이 대략 0.2 < ${\rho}$ < 0.7인 경우에 MSE 효율성이 높아짐을 밝혔다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1992.04a
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• pp.13-18
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• 1992

구조물의 동적실험을 통하여 얻은 하중과 거동에 대한 시간기록을 분석하여, 구조계의 동 특성계수들을 추정하는 기법에 대하여 연구하였다. 실험과정 및 해석모형과정의 오차를 고려하기 위하여, 하중기록과 구조거동기록간의 관계를 추계론적 자동회기 및 이동평균모형(Stochastic Auto-Regressive and Moving-Average (ARMAX) Model)음 사용하여 모형화하였다. 미지의 ARMAX 계수행렬들은 순차적 예측오차기법을 사용하여 추정하였으며, 계수추정기법의 효율성을 증진시키기 위하여, Exponential Data Weighting, Global Data Weighting 및 Square Root Estimation 기법을 활용하였다. 다중거동측정계의 예제해석을 통하여 이의 효율성을 분석하였다.