• Communications for Statistical Applications and Methods
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• 제23권1호
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• pp.1-20
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• 2016

Causal inference methodologies have been developed for the past decade to estimate the unconfounded effect of an exposure under several key assumptions. These assumptions include, but are not limited to, the stable unit treatment value assumption, the strong ignorability of treatment assignment assumption, and the assumption that propensity scores be bounded away from zero and one (the positivity assumption). Of these assumptions, the first two have received much attention in the literature. Yet the positivity assumption has been recently discussed in only a few papers. Propensity scores of zero or one are indicative of deterministic exposure so that causal effects cannot be defined for these subjects. Therefore, these subjects need to be removed because no comparable comparison groups can be found for such subjects. In this paper, using currently available causal inference methods, we evaluate the effect of arbitrary cutoffs in the distribution of propensity scores and the impact of those decisions on bias and efficiency. We propose a tree-based method that performs well in terms of bias reduction when the definition of positivity is based on a single confounder. This tree-based method can be easily implemented using the statistical software program, R. R code for the studies is available online.

• Earthquakes and Structures
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• 제18권5호
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• pp.555-565
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• 2020

The main objective of seismic codes is to prevent structural collapse and ensure life safety. Collapse probability of a structure is usually assessed by making a series of analytical model assumptions. This paper investigates the effect of finite element modeling (FEM) assumptions on the estimated collapse capacity of a reinforced concrete (RC) frame building and points out the modeling limitations. Widely used element formulations and hysteresis models are considered in the analysis. A full-scale, three-story RC frame building was utilized as the experimental model. Alternative finite element models are established by adopting a range of different modeling strategies. Using each model, the collapse capacity of the structure is evaluated via Incremental Dynamic Analysis (IDA). Results indicate that the analytically estimated collapse capacities are significantly sensitive to the utilized modeling approaches. Furthermore, results also show that models that represent stiffness degradation lead to a better correlation between the actual and analytical responses. Results of this study are expected to be useful for in developing proper models for assessing the collapse probability of RC frame structures.

• 인지과학
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• 제13권4호
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• pp.22-22
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• 2002

교육 장면이나 기업에서 창의성 개발에 대한 관심은 그 어느 때보다 높다. 본 논문에서는 창의성 개발 연구의 기저에는 창의성이 개인차를 드러내는 측정 가능한 구인이라는 가정과 창의성이 훈련에 의해 개발될 수 있는 하나의 인지적 기술이라는 가정이 있다고 보았다. 이 두 가정의 출처를 추적하고, 이 가정들의 타당성과 한계를 창의성 검사와 개발 프로그램을 통해 살펴보았다 이 두 가정은 작업 가설일 뿐 아직 경험적 증거가 미약하다는 점과 논의되었고, 경험적 근거 위에 창의성 개념을 정립하기 위한 앞으로의 연구 방향을 제안하였다.

• 인지과학
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• 제13권4호
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• pp.25-41
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• 2002

교육 장면이나 기업에서 창의성 개발에 대한 관심은 그 어느 때보다 높다. 본 논문에서는 창의성 개발 연구의 기저에는 창의성이 개인차를 드러내는 측정 가능한 구인이라는 가정과 창의성이 훈련에 의해 개발될 수 있는 하나의 인지적 기술이라는 가정이 있다고 보았다. 이 두 가정의 출처를 추적하고, 이 가정들의 타당성과 한계를 창의성 검사와 개발 프로그램을 통해 살펴보았다 이 두 가정은 작업 가설일 뿐 아직 경험적 증거가 미약하다는 점과 논의되었고, 경험적 근거 위에 창의성 개념을 정립하기 위한 앞으로의 연구 방향을 제안하였다.

• 대한가정학회지
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• 제39권11호
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• pp.161-174
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• 2001

In the 7th curriculum revision, Home Economics and Technology are combined into one subject, Practical Arts(Technology Home Economic), from 5th to 10th grades. The purpose of this study was to ewamine what perspectives home economics teachers and technology teachers have on curriculum. A questionnaire survey was carried out to the 297 middle school home economics teachers and technology teachers across the nation, to find out the differences of their perspectives on curriculum by independent variables. The findings of this study were as follows: 1) Both groups of home economics teachers and technology teachers supported interpretive, emancipators, and technical perspective on curriculum in the order named. 2) Teachers who have teaching experience of 21 years or more showed higher orientation toward technical perspective than those who have teaching experience of 10 years or less in assumptions on society, educational goal, Knowledge, and teaching-loaming method. 3) Public school teachers showed stronger orientation toward technical perspective in assumptions on teaching-learning method, and toward emancipatory perspective in assumptions on society. 4) Teachers who majored in or took charge of Technology generally had strong orientation toward technical perspective, whereas those who majored in or took charge of Home Economics oriented more toward interpretive or emancipatory than technical perspective.

• 응용통계연구
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• 제28권4호
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• pp.663-683
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• 2015

저출산과 고령화 등의 인구구조의 변화는 미래 건강보험 재정의 안전성을 위협하고 있다. 이에 본 논문에서는 2002년부터 2013년까지 국민건강보험 표본코호트 DB를 이용하여 유병율 및 진료비에 대한 통계적 모형을 추정하고 인구구조와 경제상황의 변화에 대한 다양한 미래 가정들을 반영하여 건강보험 재정의 연도별 수입과 지출을 2060년까지 추계하였다. 지출 추계에는 건강보험공단 표본 코호트 DB를 이용하여 유병율 및 진료비를 추계하였다. 유병율 모형은 VECM-LC모형을 그리고 1인당 공단 부담 진료비에 대한 추계는 이중지수평활법에 근거 하였다. 두 모형 모두를 의료기관별, 질병별, 성별, 연령별로 적합하고 경제상황의 변화에 대한 국회와 정부의 여러 가정들을 반영하여 최종 추계치를 산출하였다. 수입 추계는 고령화 속도에 대한 두 개의 다른 가정에 근거한 두 개의 미래 인구구조를 반영한 두 개의 피부양률 가정에 근거하고, 지출 추계에서와 마찬가지로 경제 상황의 변화에 대한 여러 가지 가정을 반영하여 최종 추계치를 산출하였다. 그 결과 건강보험 재정적자는 2015년 불변가격으로 2030년에는 2030조 원, 2060년에는 4070조 원이 될 것으로 추계되었다.

• 한국조사연구학회:학술대회논문집
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• 한국조사연구학회 2006년도 추계학술대회 발표논문집
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• pp.279-304
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• 2006

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.107-112
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• 2003

In general, the dynamics of autonomous underwater vehicles(AUVs) are highly nonlinear and time-varying, and the hydrodynamic coefficients of vehicles are hard to estimate accurately because of the variations of these coefficients with different navigation conditions. For this reason, in this paper, the control gain function is assumed to be unknown and the exogenous input term is assumed to be unbounded, although it still satisfies certain restrict condition. And these two kinds of wild assumptions have been seldom handled simultaneously in one system because of the difficulty of stability analysis. Under the above two relaxed assumptions, a robust neural network control scheme is presented for autonomous diving control of an AUV, and can guarantee that all the signals in the closed-loop system are UUB (uniformly ultimately bounded). Some practical features of the proposed control law are also discussed.

• International Journal of CAD/CAM
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• 제5권1호
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• pp.51-58
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• 2005

Interpreting a natural line drawing as a solid object requires simplifying assumptions in order to make the problem more tractable. Unfortunately, some of the assumptions made in the past have overly simplified the problem. Restricting the valency of vertices, and in particular allowing only trihedral vertices, distorts the problem, since algorithms which are satisfactory for the simplified problem are not satisfactory in the general case. This paper presents a test set of drawings of objects with higher-valency vertices. The intention in creating this test set is that it may be used to determine how effective various algorithms are in dealing with general (i.e. unrestricted) valency vertices.

• 대한수학회지
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• 제35권3호
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• pp.755-764
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• 1998

The least informative distributions minimizing Fisher information for location are obtained in the classes of continuously differentiable and piece-wise continuously differentiable densities with the additional restrictions on their values at the median and mode of population in the point and interval forms. The structure of these optimal solutions depends both on the assumptions of smoothness and form of characterizing restrictions of the class of distributions: in the class of continuously differentiable densities, the least informative distributions are finite and have the cosine-type form, and, in the class of piece-wise continuously differentiable densities, the least informative densities have exponential-type tails, the Laplace density in particular. The dependence of optimal solutions on the assumptions of symmetry is also analyzed.