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Use of the estimated critical values adapting a regression equation for the approximate entropy test
차경준,류제선,Cha, Kyung-Joon,Ryu, Je-Seon 한국데이터정보과학회 2002 한국데이터정보과학회지 Vol.13 No.2
The statistical testing methods have been widely recognized to determine the plain and cipher texts. In fact, the randomness for a sequence from an encryption algorithm is necessary to guarantee security and reliance of cipher algorithm. Thus, the statistical randomness tests are used to discover cipher text. In this paper, we would provide the critical value for an approximate entropy test by estimating the nonlinear regression equation when the number of sequence and the level of significance are given. Thus, we can discern plan and cipher text for real problem with given number of sequence and the level of significance. Also, we confirm the fitness of the estimated critical values from the rate of success for plain or cipher text.
An Adaptive Bandwidth Selection Algorithm in Nonparametric Regression
Kyung Joon Cha(차경준),Seung Woo Lee(이승우) 한국통계학회 1994 응용통계연구 Vol.7 No.1
커널 추정은 커널함수와 bandwidth에 의해서 결정이 된다. 그러나 평활의 정도를 조절하는 적절한 bandwidth를 찾는 것이 더욱 중요한 문제이다. 그러므로 이론적으로 최적의 bandwidth와 비교하여 실제자료에 잘 적용될 수 있는 적절한 bandwidth를 어떻게 찾느냐는 것이 문제가 된다. 본 논문에서는 평균제곱오차(mean square error)의 편의(bias)와 분산(variance)의 관계를 통하여 커널을 이용한 회귀선의 추정에 있어서 간단하고 효과적인 local bandwidth를 찾을 수 있는 알고리즘을 제안하였다. Nonparametric regression technique using kernel estimator is an attractive alternative that has received some attention, recently. The kernel estimate depends on two quantities which have to be provided by the user: the kernel function and the bandwidth. However, the more difficult problem is how to find an appropriate bandwidth which controls the amount of smoothing (see Silverman, 1986). Thus, in practical situation, it is certainly desirable to determine an appropriate bandwidth in some automatic fashion. Thus, the problem is to find a data-driven or adaptive (i.e., depending only on the data and then directly computable in practice) bandwidth that performs reasonably well relative to the best theoretical bandwidth. In this paper, we introduce a relation between bias and variance of mean square error. Thus, we present a simple and effective algorithm for selecting local bandwidths in kernel regression.
Use of the estimated critical Values adapting regression equation for the approximate entropy test
차경준(Kyung Joon Cha),류제선(Je Seon Ryu) 한국데이터정보과학회 2002 한국데이터정보과학회지 Vol.13 No.2
The statistical testing methods have been widely recognized to determine the plain and cipher texts. In fact, the randomness for a sequence from an encryption algorithm is necessary to guarantee security and reliance of cipher algorithm. Thus, the statistical randomness tests are used to discover cipher text. In this paper, we would provide the critical value for an approximate entropy test by estimating the nonlinear regression equation when the number of sequence and the level of significance are given. Thus, we can discern plan and cipher text for real problem with given number of sequence and the level of significance. Also, we confirm the fitness of the estimated critical values from the rate of success for plain or cipher text.
Modification of Boundary Bias in Nonparametric Regression
Kyung Joon Cha(차경준) 한국통계학회 1993 응용통계연구 Vol.6 No.2
커널을 이용한 회귀선의 추정은 단지 참 함수의 미분성만을 요구하는 비모수적인 회귀선의 추정방법이다. 유한구간에서 어떤 곡선의 완만한 추정곡선을 커널을 이용하여 추정할때 추정량의 전체적인 성능을 감소시키는 바운더리 문제가 발생하게 된다. 본논문에서는 바운더리 문제를 다룰수 있는 커널을 개발하였다. Gray와 Schcany(1972)의 일반화된 jackknife 방법을 이용하여 바운더리 커널을 개발하였고 또한 이 바운더리 커널이 비 바운더리 커널과 같은 수렴속도를 갖는것을 보였다. Kernel regression is a nonparametric regression technique which requires only differentiability of the true function. If one wants to use the kernel regression technique to produce smooth estimates of a curve over a finite interval, one can realize that there exist distinct boundary problems that detract from the global performance of the estimator. This paper develops a kernel to handle boundary problem. In order to develop the boundary kernel, a generalized jackknife method by Gray and Schucany (1972) is adapted. Also, it will be shown that the boundary kernel has the same order of convergence rate as non-boundary.
태아심박동 제 변수를 이용한 임신주수 추정알고리즘의 개발
차경준(Kyung Joon Cha),박영선(Young Sun Park),류제선(Je Seon Ryu),윤상순(Sang Soon Yoon),황정혜(Jung Jung Hae),정성로(Sung Ro Chung),문형(Hyung Moon),박문일(Moon Il Park) 대한산부인과학회 2001 Obstetrics & Gynecology Science Vol.44 No.11
N/A Objective : The objective of this study is to estimate gestational age by using FHR parameters after linear and nonlinear analysis of FHR data. Linear spectral decomposition has a limit to describe and analyze the nonlinear and complex physiological nature. Random processing and chaotic analysis assist to quantify some patterned energies, interaction of the physiological system in body system, which the constancy is preserved, and complexity of physical cardiovascular system. But there are no great development of new device which notify fetal age. Methods : From March 1995 to December 2000, 2,548 cases who received NST during antenatal visit were included in this study. Among these cases, 1000 cases were sampled randomly. We divided this cases into a study and a control group, 500 cases for model building set and the other 500 cases for validation set. Each FHR parameters such as baseline FHR, variability (AMP, MMR), acceleration & deceleration (15 bpm- 15 seconds), loss of signal, the number of fetal movement were analysed by using our own computerized HYFM-I, II software system. The linear and non-linear analysis of FHR were done after extracting approximate entropy (ApEn) value. Finally, we performed regression analysis and extract an equation for estimation of gestational weeks using bootstrap method. Results : We extract a following equation using above study method: Log(GA)=5.870-0.051(Sloss*)-0.065(Mean FHR*)+0.049(Mean FHR*)2-0.058(FM*)+0.048(AMP*)2+0.121(A1515*)-0.031(A1515*)2+0.036(ApEn*)2 Conclusions : Accurate dating of pregnancy, namely gestational week is very important for antenatal diagnosis in the field of perinatal medicine. This study will propose scientific research results which are useful for studying normal and morbid generating physiological fetal condition. We extract an appropriate equation for estimation of gestational weeks only using FHR parameters. We hope to compare our result with other authors` results in the near future.
문항반응이론에서 피험자 능력 및 문항모수 추정 알고리즘 개발
최항석,차경준,김성훈,박정,박영선,Choi, Hang-Seok,Cha, Kyung-Joon,Kim, Sung-Hoon,Park, Chung,Park, Young-Sun 한국통계학회 2008 Communications for statistical applications and me Vol.15 No.3
문항반응이론(Item response theory: IRT)에서는 문항이 가지고 있는 특성을 기초로 피험자의 능력을 추정하고 동시에 각 문항별 문항특성곡선(Item characteristics curve: ICC)을 이용하여 문항모수를 추정하게 된다. 그러나 모수추정에 있어서 최대 우도추정의 경우는 초기값과 다른 여러 문제들이 발생할 수 있다. 본 연구에서는 추정 문제 해결방법의 대안으로 점근적 근사화 방법(Asymptotic approximation method: AAM)을 제안한다. 이는 자료의 수가 적거나 국소 변동이 있는 경우에 효과적인 추정방법이라고 할 수 있다. 이에 개발된 'Any Assess' 시스템을 모의실험을 통하여 신뢰성을 검정하였다. Item response theory(IRT) estimates latent ability of a subject based on the property of item and item parameters using item characteristics curve(ICC) of each item case. The initial value and another problems occurs when we try to estimate item parameters of IRT(e.g. the maximum likelihood estimate). Thus, we propose the asymptotic approximation method(AAM) to solve the above mentioned problems. We notice that the proposed method can be thought as an alternative to estimate item parameters when we have small size of data or need to estimate items with local fluctuations. We developed 'Any Assess' and tested reliability of the system result by simulating a practical use possibility.
김윤수,최은선,차경준,Kim, Yun-Soo,Choi, Eun-Sun,Cha, Kyung-Joon 한국수학사학회 2008 Journal for history of mathematics Vol.21 No.4
우리나라의 출생 성비는 자연 상태에서의 출생 성비(natural sex ratio at birth)로 추정되는 105를 초과하고 있는데, 그 원인 중 하나로 남아선호사상으로 인한 인위적인 출산이 있다(e.g. 임신중절 등). 본 연구에서는 임신 중절 없이 남아를 낳을 때까지만 출산을 하려는 가정(family)들의 존재가 출생 성비를 높이는 데에 기여하는지를 알아보기 위하여, 이러한 가정들과 출생 성비(sex ratio at birth)의 관계를 분석하였다. 그 결과, 남아 한 명을 낳을 때까지만 출산을 하려는 가정의 수가 무한으로 발산할수록 출생 성비는 자연 상태에서의 출생 성비에 확률적으로 수렴하는 것을 알 수 있었다. 즉, 남아를 낳을 때까지만 출산을 하려는 가정들의 존재는 출생 성비에 영향을 미치지 않음을 확인하였다. The sex ratio at birth of South Korea is exceeding the natural sex ratio at birth, which is estimated to be about 105. One of the reasons of high sex ratio at birth is due to sex-selective abortion which is caused by strong son preference. The main objective of this study is to identify whether the families which are trying to bear children only until they acquire one son contribute to high sex ratio at birth. As a result, we obtain the theorem that if the number of such families diverge, the sex ratio at birth converges to the natural sex ratio almost surely. Therefore, we conclude that the existence of the families which are trying to bear children only until they receive one son does not affect the sex ratio at birth.