• The Korean Journal of Applied Statistics
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• v.30 no.4
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• pp.539-553
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• 2017

We propose a multi-state model to analyze semi-competing risks data with interval-censored or missing intermediate events. This model is an extension of the three states of the illness-death model: healthy, disease, and dead. The 'diseased' state can be considered as the intermediate event. Two more states are added into the illness-death model to incorporate the missing events, which are caused by a loss of follow-up before the end of a study. One of them is a state of the lost-to-follow-up (LTF), and the other is an unobservable state that represents an intermediate event experienced after the occurrence of LTF. Given covariates, we employ the Lin and Ying additive hazards model with log-normal frailty and construct a conditional likelihood to estimate transition intensities between states in the multi-state model. A marginalization of the full likelihood is completed using adaptive importance sampling, and the optimal solution of the regression parameters is achieved through an iterative quasi-Newton algorithm. Simulation studies are performed to investigate the finite-sample performance of the proposed estimation method in terms of empirical coverage probability of true regression parameters. Our proposed method is also illustrated with a dataset adapted from Helmer et al. (2001).

• The Korean Journal of Applied Statistics
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• v.23 no.2
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• pp.335-344
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• 2010

Reliability of the estimation is usually damaged in the situation where a linear regression model without spatial dependencies is employed to the spatial data analysis. In this study, we considered the conditional autoregressive model in order to construct spatial association structures and estimate the parameters via the Bayesian approaches. Finally, we compared the performances of the models with spatial effects and the ones without spatial effects. We analyzed the yearly total crime count data measured from each of 25 districts in Seoul, South Korea in 2007.

• Communications for Statistical Applications and Methods
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• v.17 no.3
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• pp.413-421
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• 2010

In this study, we considered bivariate conditional auto-regressive model taking into account spatial association as well as correlation between the two dependent variables, which are the counts of murder and burglary. We conducted likelihood ratio test for checking over-dispersion issues prior to applying spatial poisson models. For the real application, we used the annual counts of violent crimes at 25 districts of Seoul in 2007. The statistical results are visually illustrated by geographical information system.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.86.1-86.1
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• 2014

흠경각루(欽敬閣漏)는 1438년 장영실이 제작한 자동물시계로 천상의 모습을 재현한 천문시계의 역할을 갖추었다. 흠경각(欽敬閣)은 세종의 통치 철학을 세우는 중요한 공간이었다. 이곳에 설치한 흠경각루는 가산(假山) 외부에 빈풍사시의 풍경을 그려서 농사짓는 백성들의 어려움을 살필 수 있도록 하였고, 의기(倚器)를 설치하여 기울어진 그릇을 권력에 비유하여 조심하도록 하였다. 또한 12지신(支神)과 12명의 옥녀(玉女), 4신(청룡, 백호, 주작, 현무)과 4명의 옥녀, 그리고 종 북 징을 타격하여 시간을 알려주는 다양한 시보인형들과 태양운행을 살펴 볼 수 있는 종합적 연출이 가미된 당시의 첨단적 시계였다. 이러한 흠경각루의 작동은 가산 내부에 위치한 물시계와 수차에 의해서 발생된다. 물시계로부터 얻어지는 일정량의 물에 의해 수차가 회전하고, 천형장치를 활용해 회전속도를 제어할 수 있었다. 본 연구에서는 흠경각루의 동력발생과정을 유기적으로 살펴 볼 수 있도록 개념 설계를 실시하였다. 또한 3D 모델링과 기초설계도를 작도하여 실험에 활용할 수 있는 수차제어시스템 모형을 제작하였다.

• Journal of Korean Society of Transportation
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• v.26 no.5
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• pp.153-162
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• 2008

This study deals with the traffic accidents at the 4-legged signalized intersections in Cheong-ju. The purpose is to comparatively analyze the characteristics and models by the accident type using the data of 143 intersections. In pursuing the above, this study gives particular emphasis to modeling such the accidents as head on collision, rear end collision, side swipe, side right angle collision, and others. The main results are the followings. First, the overdispersion tests show that the negative binomial regression models are appropriate to the traffic accident data in the above contexts. Second, five accident models are developed, which are all analyzed to be statistically significant. Finally, the models are comparatively evaluated using the common variable(ADT) and type-specific variables.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.5 no.2
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• pp.191-196
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• 2004

Allocative efficiency measures the extents to which the technically efficient units falls shorts of achieving minimal cost. By using this measure manager can make decision about how to redistribute organizational resources to improve price efficiency. Allocative and overall efficiency are derived on the basis of budget line and cost minimization concept. The purpose of this study is to introduce the concept of allocative efficiency and propose two modified DEA models. Examples are provided to illustrate the similarities and the application procedure of the two model. By providing example and tracing the data application procedure, we found the same results but some cautions are needed to interpret the valuation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.1
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• pp.155-160
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• 1996

In this paper, we consider the discrete-time known signal detection problem under the presence of additive noise exhibiting weak dependence. We derive the locally optimum, memoryless, and one-memory detector test statistics under a seakly dependent noise model. The performance characteristics of the one-memory detector can achieve almost optimum performance at the expense of only one memory unit under the weakly dependent noise model.

• The Journal of the Acoustical Society of Korea
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• v.12 no.2E
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• pp.19-26
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• 1993

이 논문에서는 가산성 잡음과 신호 의존성 잡음이 바라는 신호와 섞일 때, 약한 복합신호를 검파하는 국소 최적 검파기의 검정 통계량을 얻었다. 순가산성 잡음 분만 아니라 비가산성 잡음도 고려하기 위하여 일반화된 관측 모델을 사용하였다. 알려진 신호, 확률 신호, 그리고 신호 의존성 잡음 성분의 상대적인 크기의 모든 경우에 대하여 국소 최적 검정통계량을 얻었다. 또한, 국소 최적 검파기의 얼개를 그림으로 나타냈다.

• The Korean Journal of Applied Statistics
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• v.8 no.2
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• pp.147-161
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• 1995

The primary objective of this paper is to review parametric models and test statistics related to overdspersion of count data. Poisson or binomial assumption often fails to explain overdispersion. We reviewed real examples of overdispersion in count data that occurred in toxicological or teratological experiments. We also reviewed several models that were suggested for implementing experiments. We also reviewed several models that were suggested for implementing the extra-binomial variation or hyper-Poisson variability, and we noted how these models were generalized and further developed. The approaches that have been suggested for the overdispersion fall into two broad categories. The one is to develop a parametric model for it, and the other is to assume a particular relationship between the variance and the mean of the response variable and to derive a score test staistics for detecting the overdispersion. Recently, Dean(1992) derived a general score test statistics for detecting overdispersion from the exponential family.

• Journal of Korean Society of Transportation
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• v.33 no.1
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• pp.100-111
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• 2015

After empirically investigating the vehicle accident risks by age groups, various programs and policies have been imposed to reduce the old's risks in other countries. In Korea, it is little known the risk level by age groups and no policy changes has been implemented even if the number of vehicle accidents occurred by the old has been rapidly rising while the total number of vehicle accidents has been decreasing. This study empirically investigates the vehicle accident risks by age groups and the results show that the old drivers over age 65 has the highest accident risk except for the young drivers below age 25. Thus, we emphasize the necessity of reinforcing the qualifications for reissuing the drive licence and programs for educating the old drivers in Korea which is facing the most rapid population aging in the world. On the other hand, various changes are needed reflecting the old drivers such as reforming the road signs, issuing a sticker and providing them incentives such that the old drivers use the public transportation instead of self-driving.