• Communications for Statistical Applications and Methods
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• v.9 no.3
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• pp.703-713
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• 2002

In longitudinal studies, outcomes are repeatedly measured over time for each subject. It is common to have missing values or dropouts for longitudinal data. In this study time trend in longitudinal data with dropouts is of concern. The confounding of time trend with dropout process is investigated through simulation studies. Some simulation results are reported for binary responses as well as continuous responses with patterns of dropouts varying. It has been found that time trend is not confounded with random dropout process for binary responses when it is estimated using GEE.

• The Journal of Engineering Geology
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• v.26 no.3
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• pp.403-411
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• 2016

A three-dimensional finite element analysis was conducted to analyze the predictable distances of a fault zone by using longitudinal displacement on tunnel face, trend line, L/C ratio, and C/C₀ ratio at tunnel crown. The analysis used 28 numerical models with various fault attitudes. As a result, those faults that have drives with dip could be predicted earliest in L/C and C/C₀ ratio analysis. And those faults that have drives against dip could be predicted earliest in L/C ratio and longitudinal displacement analysis. In addition, the fault zone ahead of tunnel was predicted in most models by using longitudinal displacement, trend line, L/C ratio, and C/C₀ ratio. However, the longitudinal displacement among these methods may be most usefully predict a fault zone since it is displacements can be measured immediately after tunnel excavation.

• Journal of The Korean Association For Science Education
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• v.19 no.2
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• pp.173-184
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• 1999

The longitudinal trend of elementary and secondary students' science process skills were investigated to monitor the progress of science learning. Science process skill test, developedin an earlier study on developing a national science process skills assessment system,was revised and administered for the study on March, 1999. Subjects were sampled nation wide according to sex and region. The results of this assessments were compared to those administered on February, 1997. The results showed little difference on science process skills among elementary school students. However, secondary students showed marked increase in science process skills. More systematic and long-term research for assessing science process skills should be planned and performed periodically to provide empirical and foundational data for educational policy making.

• Journal of The Korean Association For Science Education
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• v.19 no.2
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• pp.194-203
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• 1999

The purpose of this study was to longitudinally analyze Korean students' trend on science-related affective characteristics and provide descriptive data for improving the quality of Korean science education. In this longitudinal study. 3603 students and 4737 students were sampled in elementary and secondary schools. respectively in January 1997 and March 1998. The result showed that students' affective characteristics were decreased with statistical significance(p<0.05) during elementary and junior high school periods. but students' affective characteristics were increased during high school period. Affective characteristics of male were significantly higher than those of females' (p<0.05). Difference on affective characteristics between female and male students was being decreased by increasing grades. Students' affective characteristics in metropolitan areas were significantly higher than those in regional areas and difference between them was increased in 1999 comparing to 1997. The students' affective characteristics in 1999 were lower than those in 1997 totally.

• The Mathematical Education
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• v.55 no.4
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• pp.447-465
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• 2016

The purpose of this study is to analyze longitudinal trends of students' mathematical affective domain by use of the data mining method. For this purpose, we used the Korea education longitudinal study(KELS 2005) which was the survey data for students' achievement test, affective domain test, teachers' evaluation, and parents' evaluation from $7^{th}$ grader in the year of 2005 to $11^{th}$ grader in the year of 2010. Subjects of this study is a total of 5040 students who answered to the mathematical affective domain survey in KELS 2005. The result findings are as follows. First, students' affective domain had changed negatively as they went up to higher grade. Second, if students' affective domain had built at a certain level in $7^{th}$ grade, the level did not change easily until $11^{th}$ grade. Third, major factors of students' affective domain were shown to be self-efficacy, intrinsic motivation, efforts and patient, and time management.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.6
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• pp.825-835
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• 2019

When the tunnel is designed, the ground is classified into several grades and the corresponding support system is applied according to the support pattern table. However, a simple pattern application based on rock grade does not take into account the longitudinal stress transitions occurring at rock grade boundaries. In this study, three-dimensional numerical analysis was performed to estimate the stress change in the longitudinal rock grade change of NATM tunnel, and the influence zone of load transfer was investigated using the influence line and trend line. As a result, the downward change of rock grade in the direction of tunnel excavation occurs in the range of 0.35~0.7D from low-strength rock to high-strength rock around the grade change boundary. It is necessary to apply a downward pattern of about 1.0D to the safety direction in consideration of the influence range of 0.35D to 0.7D.

• Journal of Auto-vehicle Safety Association
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• v.10 no.1
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• pp.38-44
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• 2018

This paper presents an analysis on driving safety in lane change situation based on road driving data. Autonomous driving is a global trend in vehicle industry. LKAS technologies are already applied in commercial vehicle and researches about lane change maneuver have been actively studied. In autonomous vehicle, not only safety control issue but also imitating human driving maneuver is important. Driving data analysis in lane change situation has been usually dealt with ego vehicle information such as longitudinal acceleration, yaw rate, and steering angle. For this reason, developing safety index according to surrounding vehicle information based on human driving data is needed. In this research, driving data is collected from perception module using LIDAR, radar and RT-GPS sensors. By analyzing human driving pattern in lane change maneuver, safety index that considers both ego vehicle and surrounding vehicle state by using relative velocity and longitudinal clearance has been designed.

• Journal of Korean Institute of Industrial Engineers
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• v.39 no.3
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• pp.222-232
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• 2013

In recent years, 'technological fusion or convergence' has drawn a lot of attention of innovation researchers and governmental policy makers as the driving force of technological innovation and industrial growth. There are, however, few studies on the analysis of longitudinal trends of technological convergence and its comparison between global and national level. In this study, with the citation data of about 18 million articles, we analyzed 1) the growth of representative convergence research areas, 2) the convergence of citing patterns between research fields, and 3) the changing trend of diversity index of all research fields. We conclude that technological convergence in korea shows the relatively strong orientation to the combination of neighboring fields than that of heterogenous fields in comparison to global trend. In particular, the relatively weak activity of cognitive science and the low level of mutual exchange between arts/humanities/social sciences and natural/engineering sciences in Korea are emphasized.

• Journal of Korea Technology Innovation Society
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• v.17 no.2
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• pp.334-354
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• 2014

This study aims to analyze the research trend of Korean medicine based on social network analysis. To do this, a dataset has been collected from KCI (Korea Citation Index) database. According to the results, we have identify the longitudinal trend of the number of papers, journals, organizations and key words in this field. Moreover, based on the nodes' centrality of co-author network, we have found a core journal (i.e. Korean Journal of Oriental Physiology and Pathology), a hub institution (i.e. Kyunghee university) and two main key words (i.e. anti-oxidation and acupuncture) in the research network. In conclusion, integrating field experts' tacit knowledge in Korean medicine studies with the results of the explicit social network analysis on the research trend, we put forward further policy implications with regard to R&D strategies in this field.

• Journal of the Korean Data and Information Science Society
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• v.26 no.3
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• pp.755-762
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• 2015

One of the main objectives of the U.S. Census Bureau is the proper estimation of median household income for small areas. These estimates have an important role in the formulation of various governmental decisions and policies. Since direct survey estimates are available annually for each state or county, it is desirable to exploit the longitudinal trend in income observations in the estimation procedure. In this study, we consider Fay-Herriot type small area models which include time-specific random effect to accommodate any unspecified time varying income pattern. Analysis is carried out in a hierarchical Bayesian framework using Markov chain Monte Carlo methodology. We have evaluated our estimates by comparing those with the corresponding census estimates of 1999 using some commonly used comparison measures. It turns out that among three types of time-specific random effects the small area model with a time series random walk component provides estimates which are superior to both direct estimates and the Census Bureau estimates.