• Communications for Statistical Applications and Methods
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• v.27 no.4
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• pp.487-500
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• 2020

Insurers face increasing demands for cyber liability; entailed in part by a variety of new forms of risk of data breaches. As data breach occurrences develop, our understanding of the volatility in data breach counts has also become important as well as its expected occurrences. Volatility clustering, the tendency of large changes in a random variable to cluster together in time, are frequently observed in many financial asset prices, asset returns, and it is questioned whether the volatility of data breach occurrences are also clustered in time. We now present volatility analysis based on INGARCH models, i.e., integer-valued generalized autoregressive conditional heteroskedasticity time series model for frequency counts due to data breaches. Using the INGARCH(1, 1) model with data breach samples, we show evidence of temporal volatility clustering for data breaches. In addition, we present that the firms' volatilities are correlated between some they belong to and that such a clustering effect remains even after excluding the effect of financial covariates such as the VIX and the stock return of S&P500 that have their own volatility clustering.

• Korean Journal of Childcare and Education
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• v.15 no.3
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• pp.61-81
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• 2019

Objective: This study aimed to examine the effects of collaborative activities by utilizing picture books in order to improve the self-regulation and perspectivetaking abilities among four-year-olds. Methods: A total of 52 four-year-olds(control group 26, experimental group 26) attending two classes at D kindergarten located in B city participated in this study. Before and after the activities, all participants individually took a social perspective taking ability instrument and rated their self-regulation with a teacher. Data were analyzed by conducting ANCOVA in the way of setting pre-test scores as the covariate and post-test scores as the dependent variable. Results: First, the total and subarea of self-regulation in the experimental group was higher than the control group. Second, the cognitive and emotional perspective taking abilities in the experimental group were higher than the control group in all cares. Conclusion/Implications: The results of this study suggest that collaborative activities using picture books are effective in improving young children's selfregulation and perspective-taking abilities.

• Educational Technology International
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• v.8 no.2
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• pp.53-71
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• 2007

This study identified the effectiveness of e-learning by comparing learning outcome in conventional face-to-face lecture with the selected e-learning methods. Two e-learning contents (animation based and video based) were developed based on the rapid prototyping model and loaded onto the learning management system (LMS), which is http://www.enaged.co.kr. Fifty-four Korean agricultural high school students were randomly assigned into three groups (face-to-face lecture, animation based e-learning, and video based e-learning group). The students of the e-learning group logged on the LMS in school computer lab and completed each e-learning. All students were required to take a pretest and posttest before and after learning under the direction of the subject teacher. A one-way analysis of covariance was administered to verify whether there was any difference between face-to-face lecture and e-learning in terms of students' learning outcomes after controlling the covariate variable, pretest score. According to the results, no differences between animation based and video based e-learning as well as between face-to-face learning and e-learning were identified. Findings suggest that the use of well designed e-learning could be worthy even in agricultural education, which stresses hands-on experience and lab activities if e-learning was used appropriately in combination with conventional learning. Further research is also suggested, focusing on a preference of e-learning content type and its relationship with learning outcome.

• KDI Journal of Economic Policy
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• v.31 no.2
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• pp.1-13
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• 2009

The monetary model suggests that nominal exchange rates between two countries will be determined by important macroeconomic variables. The existence of a cointegrating relationship among these fundamental variables is the backbone of the monetary model. In a recent paper, Rapach and Wohar (2002, Journal of International Economics) advance the literature by testing for linear cointegration in the monetary model using a century of data to increase power. They find evidence of cointegration in five or six of ten countries. We extend their work to the nonlinear framework by performing threshold cointegration tests that allow for asymmetric adjustments in two regimes. Asymmetric adjustments in exchange rates can occur, for example, if transactions costs are present or if policy makers react asymmetrically to changing fundamentals. Moreover, whereas Rapach and Wohar (2002) found it necessary to exclude the relative output variable in some cases to maintain the validity of their cointegration tests, we can include this variable as a stationary covariate to increase power. Overall, using their same long-span data, we find more support for cointegration in a nonlinear framework.

• Journal of Distribution Research
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• v.12 no.4
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• pp.1-25
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• 2007

The purpose of this study is to provide the strategic implication of the Korean open air market by examining the factors affecting customer loyalty for various market segments as their competitive environment becomes more turbulent. We have undertaken empirical research that uses the methodology of a mixture regression modeling, as a way to ascertain the determinants of customer loyalty toward the Korean open air market, which should form the base of strategy for each segment. We construct a mixture regression model which uses perceived the Korean open air market value dimensions as explanatory variables, an income as a covariate variable, and a customer loyalty as a dependent variable. The analysis of results show that customers are statistically divided into four segments: 'Accessibility'(33.7%), 'Price'(29.7%), 'Shopping environment,'(22.0%), and 'Merchandising,'(14.5%) groups. The findings also showed that parameter estimates are different for each group, which indicates that the sensitivity to changes in the Korean traditional market perceived value and the income variable affecting customer loyalty vary among segments.

• Journal of The Korean Association For Science Education
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• v.17 no.2
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• pp.139-148
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• 1997

This study investigated the influences of the cooperative learning strategies upon students' achievement and their perceptions of learning environments in a middle school physical science course. Prior to instruction, the Group Assessment of Logical Thinking was administered, and its score was used as a blocking variable. Mid-term examination score was used as a covariate. For the treatment group with heterogeneous grouping, cooperative learning instruction (the Learning Together model) was used, which emphasized group reward, individual accountability, and role division. For the control group, traditional instruction was used. After instruction, an achievement test consisting of three subtests (knowledge, understanding, and application), and the perception questionnaire of classroom and laboratory environments, were administered. ANCOVA results revealed that there was a significant interaction between instruction and the level of logical reasoning ability although there were no significant differences in all three subtest scores of the achievement test. For the concrete operational reasoners, the treatment group performed better in the subtests of understanding and application than the control group. For students at the formal and transition levels, however, the treatment group scored lower than the control group. Significant interactions were also found in the perceptions of classroom environment and laboratory environment. For the concrete operational reasoners, the treatment group showed more positive perception than the control group. For the students at the formal and transition levels, the control group had positive perception than the treatment group. Educational implications are discussed.

• Journal of The Korean Association For Science Education
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• v.17 no.2
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• pp.179-189
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• 1997

In this study, a conceptual change model for effective laboratories was developed and its instructional effect on students' achievement, the acquisition of scientific conceptions, and the attitudes toward science was investigated. Considering several conceptual change models in literature and Korean educational situations, the conceptual change model was developed. The model consists of 5 stages; preliminary, prediction, exploration, consolidation and reconstruction, and application. The treatment and control groups (2 classes) were selected from a middle school in Seoul, and taught about the changes of states, density, and dissolution for three weeks. Prior to instruction, the Group Assessment of Logical Thinking and the Learning Approach Questionnaire were administered, and their scores were used as covariate and / or blocking variable. To examine students' alternative conceptions before the instructions, a pre-conceptions test was also administered. After the instructions, students' achievement, the acquisition of scientific conceptions, and the attitudes toward science were measured with a researcher-made achievement test, a post-conceptions test, and the subtests of the Test of Science-Related Attitudes, respectively. The results indicated that the score of the treatment group was significantly higher than that of the control group in the post-conceptions test. The students in the treatment group had also less alternative conceptions than those in the control group. However, there were no significant differences for the achievement and the attitudes toward science. Educational implications are discussed.

• Journal of The Korean Association For Science Education
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• v.17 no.1
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• pp.45-53
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• 1997

The purpose of this study was to investigate the instructional effects of a problem solving model on students' achievement, science process skills, and perceptions of science activities. The problem solving model was developed on the basis of the SSCS (Search, Solve, Create, Share) problem solving model while considering Korean educational situations under a national curriculum. The model developed is composed of 4 stages; identify, solve, create, and share. In this research, the treatment and control groups (6 classes) were selected from a middle school in Seoul and taught about the separation of mixture for four weeks. Prior to instruction, the Group Assessment of Logical Thinking and the Learning Approach Questionnaire were administered, and their scores were used as covariate and blocking variable, respectively. During instruction, classroom observations for each group were conducted with a researcher-made checklist. Immediately following the instructions, students' achievement, science process skills, and perceptions of science activities were measured by a researcher-made achievement test, the Middle Grades Integrated Science Process Skills Test(MIPT), and the Perceptions of Science Activities Questionnaire, respectively. The results indicated that students in the treatment group achieved significantly better than those in the control group. Although students in the treatment group were found to use more science process skills correctly during their science activities, the MIPT scores of the treatment group were not significantly higher than those of the control group. No interaction with students' learning approach was found for both students' achievement and science process skills. On the questionnaire of students' perceptions of science activities, the treatment group showed more positive perceptions and interest than the control group. Educational implications are discussed.

• Journal of The Korean Association For Science Education
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• v.17 no.3
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• pp.313-321
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• 1997

The purpose of this study was to investigate the instructional effect of a four-stage problem solving approach visually emphasizing the molecular level of matter upon students' conceptions and problem solving ability. On the basis of the research results regarding molecular representation in learning chemistry, problem-solving instruction, and the effect of visual materials, the instructional strategy was developed while considering Korean educational situations. The treatment and control groups (2 classes) were selected from a girls' high school in Seoul and taught about stoichiometry, gas, liquid, solid, and solution for 13 weeks. For the treatment group, 52 charts were supplied in order to emphasize the molecular level of matter and/or 4 stage problem solving strategy-understanding, planning, solving, and reviewing. For the control group, traditional instruction was used. Before the instructions, the Group Assessment of Logical Thinking and the Spatial Ability Test were administered, and their scores were used as covariate and blocking variable, respectively. After the instructions, students' conceptions and problem solving ability were measured by the Chemistry Conceptions Test (CCT) and the Chemistry Problem Solving Ability Test (CPSAT), respectively. The results indicated that the CCT scores of the treatment group were significantly higher than those of the control group. The students in the treatment group also exhibited less misconceptions than those in the control group. However, there was not significant difference for the CPSAT scores. No interaction with students' spatial ability was found for both students' conceptions and problem solving ability. Educational implications are discussed.

• Journal of Gastric Cancer
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• v.14 no.4
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• pp.259-265
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• 2014

Purpose: Survival analysis of gastric cancer patients requires knowledge about factors that affect survival time. This paper attempted to analyze the survival of patients with incomplete registered data by using imputation methods. Materials and Methods: Three missing data imputation methods, including regression, expectation maximization algorithm, and multiple imputation (MI) using Monte Carlo Markov Chain methods, were applied to the data of cancer patients referred to the cancer institute at Imam Khomeini Hospital in Tehran in 2003 to 2008. The data included demographic variables, survival times, and censored variable of 471 patients with gastric cancer. After using imputation methods to account for missing covariate data, the data were analyzed using a Cox regression model and the results were compared. Results: The mean patient survival time after diagnosis was $49.1{\pm}4.4$ months. In the complete case analysis, which used information from 100 of the 471 patients, very wide and uninformative confidence intervals were obtained for the chemotherapy and surgery hazard ratios (HRs). However, after imputation, the maximum confidence interval widths for the chemotherapy and surgery HRs were 8.470 and 0.806, respectively. The minimum width corresponded with MI. Furthermore, the minimum Bayesian and Akaike information criteria values correlated with MI (-821.236 and -827.866, respectively). Conclusions: Missing value imputation increased the estimate precision and accuracy. In addition, MI yielded better results when compared with the expectation maximization algorithm and regression simple imputation methods.