• Communications for Statistical Applications and Methods
• /
• 제9권2호
• /
• pp.533-542
• /
• 2002

In this paper, a covariate adjusted logrank test is considered for censored paired data under the Cox proportional hazard model. The proposed score test resembles the adjusted logrank test of Tsiatis, Rosner and Tritchler (1985), which is derived from the partial likelihood. The dependence structure for paired data is accommodated into the test statistic by using' sum of square type' variance estimators. Several weight functions are also considered, which produce a class of covariate adjusted weighted logrank tests. Asymptotic normality of the proposed test is established and simulation studies with moderate sample size show the proposed test works well, particularly when there are dependence structure between treatment and covariates.

• 산업경영시스템학회지
• /
• 제20권44호
• /
• pp.333-341
• /
• 1997

The purpose of this paper is to compare the manufacturing process with random covariate using multiple comparison procedure. The methodology that compares each manufacturing process by inspecting the number of nonconforming items out of k-treatment, has serveral limitations and problems according to the method and contect of the analysis. The proper way of analysis, therefore, could be obtained by the multiple comparison procedure of simultaneous confidence region of variance components. Effections that affect a manufactuing process may be predictive of responce to treatments are called covariates. In the study of comparing several treatments, prsense of covariate may bias the estimates of treatment effects.

• Communications for Statistical Applications and Methods
• /
• 제12권3호
• /
• pp.705-712
• /
• 2005

Biplot is a graphical display of the rows and columns of an n${\times}$p data matrix. In particular, Gabriel (1995) suggested the MANOVA biplot using singular value decomposition (SVD) with the averages of response variables according to treatment groups. But his biplot may cause wrong results by disregarding them when there exist covariate effects. In this paper, we will provide the MANCOA biplot based on the SVD with the parameter estimates for MANCOVA model when there exist covariate effects.

• Journal of the Korean Statistical Society
• /
• 제23권1호
• /
• pp.53-62
• /
• 1994

When a comparison is made with respect to the unknown best treatment, Hsu (1984, 1985) proposed the so called multiple comparisons procedures with the best in the analysis of variance model. Applying Hsu's results to the analysis of covariance model, simultaneous confidence intervals for multiple comparisons with the best in a balanced one-way layout with a random covariate are developed and are applied to a real data example.

• 한국통계학회:학술대회논문집
• /
• 한국통계학회 2005년도 춘계 학술발표회 논문집
• /
• pp.285-290
• /
• 2005

Biplot is a graphical display of the rows and columns an $n{\time}p$ data matrix. In particular, Gabriel(1981) suggested The MANOVA BIPLOT using singular value decomposition (SVD) with the averages of response variables according to treatment groups. But his biplot may cause wrong results by disregarding them when there exists covariate effects. In this paper, we will provide the MANCOVA BIPLOT based on the SVD with the parameter estimates for MANCOVA model when there exist covariate effects.

• 응용통계연구
• /
• 제24권3호
• /
• pp.559-566
• /
• 2011

행렬도는 이원표 자료행렬의 행과 열을 탐색하기에 유용한 그래프적 방법이다. 특히, 정준상관 행렬도는 정준상관분석의 결과를 이용하여 두 변수군과 개체간의 관계를 기하적으로 살펴볼 수 있다. 그 반면에 자료의 성격에 따라 세개 이상의 변수군이 존재하는 경우에는 정준상관분석의 개념에서 확장한 일반화 정준상관분석을 이용하여 일반화 정준상관 행렬도를 고려할 수 있다. 그러나 자료의 성격에 따라 두 변수군 외에 이들 두 변수군에 선형적 영향을 미치는 공변량변수로 이루어진 다른 한 변수군이 존재하는 경우에, 일반화 정준상관 행렬도를 적용한다면 공변량변수군의 영향력 때문에 주 관심인 두 변수군에 대하여 잘못 해석할 수 있다. 따라서 본 연구에서는 Rao (1969)의 공변량 변수군의 영향력을 제거한 편정준상관분석을 살펴보고, 이를 기하적으로 해석하기 위한 편정준상관 행렬도를 제안한다.

• Nuclear Engineering and Technology
• /
• 제50권1호
• /
• pp.107-115
• /
• 2018

To ensure the structural integrity of nuclear power plants, it is essential to predict the lifetime of Alloy 182 weld, which is used for welding in nuclear reactors. The lifetime of Alloy 182 weld is directly related to the crack initiation time. Owing to the large time scatter in most crack initiation tests, a probabilistic model, such as the Weibull distribution, has mainly been adopted for prediction. However, since statistically more advanced methods than current typical methods may be applied, we suggest a statistical procedure for parameter estimation of the crack initiation time of Alloy 182 weld, considering right-censored data and the covariate effect. Furthermore, we suggest a procedure for uncertainty evaluation of the estimators based on the bootstrap method. The suggested statistical procedure can be applied not only to Alloy 182 weld but also to any material degradation data set including right-censored data with covariate effect.

• Communications for Statistical Applications and Methods
• /
• 제19권1호
• /
• pp.97-105
• /
• 2012

일반화 정준상관 행렬도(generalized canonical correlation biplot)는 정준상관분석에서 세 변수군 이상에 의해서 측정된 다변량 자료에서 변수 집단 간의 관계와 개체들의 관계를 탐색하기 위한 2차원 그림이다. 최근에 이를 활용하여 최태훈과 최용석 (2010)은 2004년 대한테니스협회(KTA)에 등록된 남자선수들 중 상위 50명을 대상으로 세 변수군인 체격요인변수군, 체력요인변수군 그리고 기초기술요인변수군의 상호 연관성을 살펴보았다. 그러나 이들 분석에서 체격요인변수군이 나머지 두 변수군과 독립적이지 못하고 선형적 영향을 미치는 것으로 판단되어 이를 공변량변수군으로 고려하였다. 이와같이 세 변수군에서 한 변수군이 공변량(covariate)으로 영향을 주는 경우 이를 제거한 정준상관분석을 편(partial)정준상관분석이라 하며 이와 관련된 편정준상관 행렬도를 염아림과 최용석 (2011)은 제안하였다. 본 연구에서는 최태훈과 최용석(2010)의 분석에서 체격요인변수군의 영향을 제거하고 체력요인변수군과 기초기술요인변수군의 관계를 살펴보는 편정준상관 행렬도의 활용의 예를 보이고 기존 연구의 일반화 정준상관 행렬도, 편정준상관 행렬도, 정준상관 행렬도의 결과를 서로 비교하고자 한다. 덧붙여 이들 행렬도간의 형상변동 차이를 프로크러스티즈 분석을 활용하여 비교하고자 한다.

• Communications for Statistical Applications and Methods
• /
• 제27권1호
• /
• pp.37-46
• /
• 2020

Recurrent event data frequently occur in clinical studies, demography, engineering reliability and so on (Cook and Lawless, The Statistical Analysis of Recurrent Events, Springer, 2007). Sometimes, two or more different but related type of recurrent events may occur simultaneously. In this study, our interest is to estimate the covariate effect on bivariate recurrent event times with zero inflations. Such zero inflation can be related with susceptibility. In the context of bivariate recurrent event data, furthermore, such susceptibilities may be different according to the type of event. We propose a joint model including both two intensity functions and two cure rate functions. Bivariate frailty effects are adopted to model the correlation between recurrent events. Parameter estimates are obtained by maximizing the likelihood derived under a piecewise constant hazard assumption. According to simulation results, the proposed method brings unbiased estimates while the model ignoring cure rate models gives underestimated covariate effects and overestimated variance estimates. We apply the proposed method to a set of bivariate recurrent infection data in a study of child patients with leukemia.

• 한국통계학회:학술대회논문집
• /
• 한국통계학회 2002년도 추계 학술발표회 논문집
• /
• pp.197-201
• /
• 2002

The healthy worker effect is an important issue in occupational epidemiology. We proposed a new statistical method to test the relationship between exposure and time to death in the presence of the healthy worker effect. In this study, we considered the healthy worker hire effect to operate as a confounder and the healthy worker survival effect to operate as a confounder and an intermediate variable. The basic idea of the proposed method reflects the length bias-sampling caused by changing one's employment status. Simulation studies were also carried out to compare the proposed method with the Cox proportional hazards models. According to our simulation studies, both the proposed test and the test based on the Cox model having the change of the employment status as a time-dependent covariate seem to be satisfactory at an upper 5% significance level. The Cox models, however, are inadequate with the change, if any, of the employment status as time-independent covariate. The proposed test is superior in power to the test based on the Cox model including the time-dependent employment status.