• Journal of the Korean Data and Information Science Society
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• 제23권4호
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• pp.643-648
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• 2012

여러 임상자료를 이용하여 반응변수와 설명변수간의 관계를 규명하는 분석이 많이 이루어지고 있다. 이를 위해서 회귀분석이 흔히 사용되고 있으며, 이를 통해 설명변수가 반응변수를 얼마나 설명하는지 또한 모형이 얼마나 자료에 적합한지에 대해 분석하고 있다. 그러나 임상자료로 분석된 회귀모형에 대한 타당성 확인은 대부분 분석된 회귀모형이 얼마나 자료를 설명하는가를 나타내는 결정계수만을 살펴보는 것에 그치고 있다. 결정계수 이외의 다른 방법으로도 분석된 회귀모형의 회귀계수에 대한 타당성을 확인할 필요가 있다. 따라서 본 논문에서는 잭나이프 회귀분석과 붓스트랩 회귀분석을 이용하여 임상자료로 분석한 회귀모형의 회귀계수에 대한 타당성을 확인하는 방법을 소개하고자 한다.

• 대한화장품학회:학술대회논문집
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• 대한화장품학회 2003년도 IFSCC Conference Proceeding Book I
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• pp.73-84
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• 2003

Skin aging process on pre-menopausal women is a problem that needs to be prevented as early as possible. The decrease of oestrogen level which is one of the intrinsic factors of the skin aging process will affect the skin biological process, due to oestrogen receptors on the skin. A number of researches conducted on pre-menopausal women with the allocation of oestrogen hormone resulted in delaying the skin aging process. The administration of soy isoflavon, a phytoestrogen found in daily food, on pre-menopausal women is hoped to be able to prevent skin aging process, even clinically or molecular biologically. This research aims to explain the benefit of administering of soy isoflavon on skin aging process. The design of the research is randomised controlled trial (RCT). As many as 60 pre-menopausal women were collected with simple random sampling method. Soy isoflavon is an independent variable, while skin aging process is a dependent variable assessed from the hydration, sebum level, average roughness, depth of wrinkles, skin clarity, length of the telomere. Analysis was conducted using t and MANDVA tests and.the result showed a significance (F = 10,439; p = 0,001) over the allocation of soy isoflavon to the whole variable dependent, including the telomere length and the skin hydration, meant that allocation of soy isoflavon could delay skin aging process.

• 유통과학연구
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• 제20권4호
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• pp.95-100
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• 2022

Purpose: This study aimed to investigate whether distribution and service companies maintained their accounting information quality and provided reliable information despite the economic changes occurring after the outbreak of the COVID-19 pandemic in Korea. The distribution industry has enjoyed increased demand as many companies expanded their untact distribution channels, including to online sales. However, as the pandemic drags on, their future prospects remain uncertain. Research design, data, and methodology: In this study, we define 2018-2019 as the "pre COVID-19 period" and 2020 as the "post COVID-19 period." An empirical analysis was performed using a regression model that includes POST, the independent variable, indicating the post COVID-19 period, and discretionary accruals(DA), a proxy for earnings management, as a dependent variable. Results: The analysis shows that the coefficient of POST is significantly positive (+) for the dependent variable DA. This finding suggests that distribution and service companies engaged in more earnings management during the post COVID-19 period than during the pre COVID-19 period, indicating their awareness of the uncertainty of future business performance as the pandemic persists. An additional analysis confirmed that smaller companies with fewer stakeholders and higher information asymmetry tend to engage more in earnings management than larger companies.

• 한국시스템다이내믹스연구
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• 제8권2호
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• pp.25-49
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• 2007

An important assumption of the classical linear regression model is that the disturbances appearing in the population regression function are homoskedastic; that is, they all have the same variance. If we persist in using the usual testing procedures despite heteroskedasticity, what ever conclusions we draw or inferences we make be very misleading. The contribution of this paper will be to the concrete procedure of the proper estimation when the heteroskedasticity does exist in the data, because the quality of dependent variable predictions, i.e., the estimated variance of the dependent variable, can be improved by giving consideration to the issues of regional homogeneity and/or heteroskedasticity across the research area. With respect to estimation, specific attention should be paid to the selection of the appropriate strategy in terms of the auxiliary regression model. The paper shows that by testing for heteroskedasticity, and by using robust methods in the presence of with and without heteroskedasticity, more efficient statistical inferences are provided.

• Structural Engineering and Mechanics
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• 제14권6호
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• pp.661-677
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• 2002

The subject of this investigation is to study the buckling of cross-ply laminated orthotropic cylindrical thin shells with variable elasticity moduli and densities in the thickness direction, under external pressure, which is a power function of time. The dynamic stability and compatibility equations are obtained first. These equations are subsequently reduced to a system of time dependent differential equations with variable coefficients by using Galerkin's method. Finally, the critical dynamic and static loads, the corresponding wave numbers, the dynamic factors, critical time and critical impulse are found analytically by applying a modified form of the Ritz type variational method. The dynamic behavior of cross-ply laminated cylindrical shells is investigated with: a) lamina that present variations in the elasticity moduli and densities, b) different numbers and ordering of layers, and c) external pressures which vary with different powers of time. It is concluded that all these factors contribute to appreciable effects on the critical parameters of the problem in question.

• Communications for Statistical Applications and Methods
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• 제24권3호
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• pp.291-301
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• 2017

It is well known in a small sample that the maximum likelihood (ML) approach for variance components in the general linear model yields estimates that are biased downward. The ML estimate of residual variance tends to be downwardly biased. The underestimation of residual variance, which has implications for the estimation of marginal effects and asymptotic standard error of estimates, seems to be more serious in some limited dependent variable models, as shown by some researchers. An alternative frequentist's approach may be restricted or residual maximum likelihood (REML), which accounts for the loss in degrees of freedom and gives an unbiased estimate of residual variance. In this situation, the REML estimator is derived in a censored regression model. A small sample the REML is shown to provide proper inference on regression coefficients.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 D
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• pp.2212-2214
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• 2004

Robust stable analysis with the system bounded parameteric variation is very important among the various control theory. This study is to investigate the robust stable conditions using the quadratic form Lyapunov function in which the coefficient matrix is affined linear system. The quadratic stability using the quadratic form Lyapunov function is not investigated yet. The Lyapunov unction is robust stable not to be dependent by the variable parameters, which means that the Lyapunov function is conservative. We suggest the robust stable conditions in the Lyapunov function in which the variable parameters are dependent in order to reduce the conservativeness of quadratic stability.

• 무역상무연구
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• 제77권
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• pp.195-214
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• 2018

In order to analyze the current status of trade with Korea and FTA partner countries, the Trade Intensity Index and the Market Comparative Advantage index were calculated and analyzed using panel gravity model. In the case of trade, trade intensity index has been strengthened according to each FTA enforecement, and in some cases, trade inensity has been weakened. In the case of the comparative advantage index, there was a case in which the comparative advantage was strengthened or the comparative advantage was not significantly changed according to each Chapter of HS code. This means that the Korea's FTA enforcement effect has not directly affected the increase of the trade intensity and the increase of the market comparative advantage index. The panel gravity model using the trade intensity and the comparative advantage index as the dependent variable and the trade volume between the two countries as the dependent variable was analyzed.

• Structural Engineering and Mechanics
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• 제60권4호
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• pp.707-727
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• 2016

In this paper, thermal vibration of a nonlocal functionally graded (FG) plates with arbitrary boundary conditions under linear and non-linear temperature fields is explored by developing a refined shear deformation plate theory with an inverse cotangential function in which shear deformation effect was involved without the need for shear correction factors. The material properties of FG nanoplate are considered to be temperature-dependent and graded in the thickness direction according to the Mori-Tanaka model. On the basis of non-classical higher order plate model and Eringen's nonlocal elasticity theory, the small size influence was captured. Numerical examples show the importance of non-uniform thermal loadings, boundary conditions, gradient index, nonlocal parameter and aspect and side-to-thickness ratio on vibrational responses of size-dependent FG nanoplates.

• 한국항해항만학회지
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• 제28권5호
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• pp.373-384
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• 2004

The purpose of this research is to introduce the concept of "relationship formation factors" in inter-firm relations and to empirically demonstrate that they are effective in improving the relationship results by means of an mediating variable. Therefore, the basic model of this study consists of the independent, mediating, and dependent variables. First, the independent variables, that is, the relationship formation factors, are further classified into three components. transactional, relational, and environmental characteristics. Then, the study empirically examines how each of the three components influences the dependent variable. that is, the business performance(Load Factor), by way of the mediating variables, that is, trust and relationship commitment.