• Communications for Statistical Applications and Methods
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• 제20권6호
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• pp.455-466
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• 2013

In nested case-control studies, the most common way to make inference under a proportional hazards model is the conditional logistic approach of Thomas (1977). Inclusion probability methods are more efficient than the conditional logistic approach of Thomas; however, the epidemiology research community has not accepted the methods as a replacement of the Thomas' method. This paper promotes the inverse probability weighting method originally proposed by Samuelsen (1997) in combination with an approximate jackknife standard error that can be easily computed using existing software. Simulation studies demonstrate that this approach yields valid type 1 errors and greater powers than the conditional logistic approach in nested case-control designs across various sample sizes and magnitudes of the hazard ratios. A generalization of the method is also made to incorporate additional matching and the stratified Cox model. The proposed method is illustrated with data from a cohort of children with Wilm's tumor to study the association between histological signatures and relapses.

• Communications for Statistical Applications and Methods
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• 제23권6호
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• pp.555-562
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• 2016

Interval censored data often occur in an observational study where the subject is followed periodically. Instead of observing an exact failure time, two inspection times that include it are available. There are several methods to analyze interval censored failure time data (Sun, 2006). However, in the presence of competing risks, few methods have been suggested to estimate covariate effect on interval censored competing risk data. A sub-distribution hazard model is a commonly used regression model because it has one-to-one correspondence with a cumulative incidence function. Alternatively, Klein and Andersen (2005) proposed a pseudo-value approach that directly uses the cumulative incidence function. In this paper, we consider an extension of the pseudo-value approach into the interval censored data to estimate regression coefficients. The pseudo-values generated from the estimated cumulative incidence function then become response variables in a generalized estimating equation. Simulation studies show that the suggested method performs well in several situations and an HIV-AIDS cohort study is analyzed as a real data example.

• Journal of the Korean Statistical Society
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• 제16권2호
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• pp.80-91
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• 1987

Minimum $L_i$ norm estimation is a robust procedure ins the sense that it leads to an estimator which has greater statistical eficiency than the least squares estimator in the presence of outliers. And the $L_1$ norm estimator has some desirable statistical properties. In this paper a new computational procedure for $L_1$ norm estimation is proposed which combines the idea of reweighted least squares method and the linear programming approach. A modification of the projective transformation method is employed to solve the linear programming problem instead of the simplex method. It is proved that the proposed algorithm terminates in a finite number of iterations.

• 대한기계학회논문집B
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• 제37권11호
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• pp.1053-1060
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• 2013

본 연구의 목적은 원자력 발전소에서 사용되는 동력구동밸브의 패킹 마찰력 예측에 대한 적절한 방법을 찾는 것이다. 밸브의 패킹은 스템을 통한 누설을 방지하는 것이 목적이나 누설방지를 위하여 글랜드 너트 강하게 조여줄 경우 패킹의 마찰력으로 인하여 밸브 작동성이 떨어지게 된다. 본 연구에서 패킹 마찰력 예측을 위하여 실험적 방법과 통계적 방법을 사용하였다. 실험적 방법은 패킹 조합의 fY값 측정후 현장 밸브에 적용하였으며, 통계적 방법은 과거 10년간의 안전관련 밸브의 진단시험 데이터의 패킹 마찰력값을 표본으로 신뢰구간을 만들어 분석에 이용하였다. 두 방법 모두 실측값과는 상당한 차이를 보였으나 fY값 측정을 통한 실험적 방법 보다는 과거 진단시험 데이터를 이용한 예측이 좀 더 정확한 결과를 보였다.

• 지질공학
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• 제24권2호
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• pp.191-199
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• 2014

We describe a method for detecting slope instability in flume tests using pore pressure and water content data in conjunction with a statistical control chart analysis. Specifically, we conducted univariate statistical analysis on x-MR control chart data (pore pressure and water content) collected at several points along the flume slope, which we separated into three parts: upper, middle, and lower. To assess our results in the context of landslide forecasting and warning systems, we applied control limit lines at $1{\sigma}$, $2{\sigma}$, and $3{\sigma}$ levels of uncertainty. In doing so, we observed that dispersion time varies depending on the control limit line used. Moreover, the detection of instabilities is highly dependent on the position and type of sensor. Our findings indicate that different characteristics of the data on various factors predict slope failure differently and these characteristics can be identified by univariate statistical analysis. Therefore, we suggest that a univariate statistical approach is an effective method for the early detection of slope instability.

• 응용통계연구
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• 제29권6호
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• pp.1041-1059
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• 2016

학술 연구나 정책 입안 등을 위한 심층적 자료 활용의 확대는 동시에 개별 정보 노출에 대한 염려도 증가시킨다. 때문에 최근 이십여 년 간 통계적 노출제어(정보보호) 분야에서 많은 논문들이 발표되었다. 본 논문은 그러한 연구 내용들을 정리하여 국내 통계인들과 기관들에게 소개하고자 한다. 주요 내용으로 국소통합이나 잡음추가와 같은 전통적인 매스킹 기법 뿐만 아니라, 온라인 자료 분석 시스템에서의 정보보호 처리, 차등정보보호를 통한 노출제어 및 재현자료를 활용한 정보보호 대안 모색에 대해 다룬다. 또한 각각의 주제에 대한 방법론 소개와 함께 활용 사례 및 장단점을 논의하였다. 본 논문이 실제적인 통계적 노출제어 문제를 고민하는 통계인들에게 도움이 되기를 바란다.

• Nuclear Engineering and Technology
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• 제54권5호
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• pp.1606-1615
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• 2022

For investigating whether the MARSSIM nonparametric test has sufficient statistical power when a site has a specific contamination distribution before conducting a final status survey (FSS), a novel approach was proposed to predict the release probability of the site. Five distributions were assumed: lognormal distribution, normal distribution, maximum extreme value distribution, minimum extreme value distribution, and uniform distribution. Hypothetical radioactivity populations were generated for each distribution, and Sign tests were performed to predict the release probabilities after extracting samples using Monte Carlo simulations. The designed Type I error (0.01, 0.05, and 0.1) was always satisfied for all distributions, while the designed Type II error (0.01, 0.05, and 0.1) was not always met for the uniform, maximum extreme value, and lognormal distributions. Through detailed analyses for lognormal and normal distributions which are often found for contaminants in actual environmental or soil samples, it was found that a greater statistical power was obtained from survey units with normal distribution than with lognormal distribution. This study is expected to contribute to achieving the designed decision error when the contamination distribution of a survey unit is identified, by predicting whether the survey unit passes the statistical test before undertaking the FSS according to MARSSIM.

• 대한기계학회논문집A
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• 제34권8호
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• pp.989-996
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• 2010

통계적 회귀모델과 보간모델은 구조공학 분야에서 실제실험과 전산실험의 결과로부터 자료를 분석하고 응답을 예측하기 위해 적용되었으며 최근 10 년 동안 다양한 설계방법론들과 함께 발전해왔다. 그러나 그들은 구조물의 크기와 형상과 같은 공간변수에 대해서만 취급해왔고 시간변수에 따라 변하는 시간-변화 동적응답을 고려할 수 없었다. 본 연구에서는 공간변수와 시간변수를 모두 취급하여 시간-변화 동적응답을 고려할 수 있는 다중응답접근법 기반 통계적 공간-시간 메타모델을 제안한다. 대표적 회귀모델인 반응표면모델과 보간모델인 크리깅모델을 구조공학 예제의 시간-변화 동적응답에 적용한다. 또한 제안한 방법의 성능을 검증하기 위해 실제함수와의 비교를 통해 두 통계적 공간-시간 메타모델의 정확성을 비교한다.

• 품질경영학회지
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• 제35권4호
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• pp.159-165
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• 2007

Using statistical methods a change-point analysis of oil supply disruption is conducted. The statistical distribution of oil supply disruption is a weibull distribution. The detection of the change-point is applied to Bayesian method and weibull parameters are estimated through Markov chain monte carlo and parameter approach. The statistical approaches to the estimation for the change-point and weibull parameters is implemented with the sets of simulated and real data with small sizes of samples.

• 말소리와 음성과학
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• 제1권4호
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• pp.133-144
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• 2009

This paper presents a method for constructing and using transliteration rules which are based on Phonics, an instructional method for speaking and writing English letters. Conventional approaches to automatic transliteration often focused on statistical methods. However, the construction or the collection of correct transliteration examples is always the bottleneck of the statistical transliteration model. Also, in practical domains where the collection of such data is very difficult, such as education and tourism, it is reasonable to build a system without much qualified data. Furthermore, compared with Korean orthography of borrowed foreign words, the proposed approach is much easier to construct, and can generate more refined rules. The experimentation result shows that the proposed approach can improve the performance of a statistical-based transliteration system.