• Communications for Statistical Applications and Methods
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• v.23 no.4
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• pp.287-296
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• 2016

Subjects on one side of the covariate population can be allocated to the inferior treatment when there is interaction between the covariate and treatment along with a response-adaptive (RA) design without covariate adjustment. An RA design allows a newly entered subject to have a better chance so that the subject is treated by a superior treatment based on cumulative information from previous subjects. A covariate-adjusted response-adaptive (CARA) is the same as RA design and additionally adjusts the allocation based on individual covariate information. A comparison has been made for the sequential estimation procedure with and without covariate adjustment to see how ignoring significantly interactive covariate affects the correct treatment allocation. Using logistic models, we present simulation results regarding the coverage probability of treatment effect, correct allocation, and stopping time.

• Journal of the Korean Data and Information Science Society
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• v.26 no.1
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• pp.217-227
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• 2015

In observational study, handling confounders is a primary issue in measuring treatment effect of interest. Historically, a regression with covariate adjustment (covariate-adjusted regression) has been the typical approach to estimate treatment effect incorporating potential confounders into model. However, ever since the introduction of the propensity score, covariate-adjusted regression has been gradually replaced in medical literatures with various balancing methods based on propensity score. On the other hand, there is only a paucity of researches assessing propensity score methods compared with the covariate-adjusted regression. This paper examined the performance of propensity score methods in estimating risk difference and compare their performance with the covariate-adjusted regression by a Monte Carlo study. The study demonstrated in general the covariate-adjusted regression with variable selection procedure outperformed propensity-score-based methods in terms both of bias and MSE, suggesting that the classical regression method needs to be considered, rather than the propensity score methods, if a performance is a primary concern.

• Communications for Statistical Applications and Methods
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• v.16 no.1
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• pp.103-113
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• 2009

Weighting is a common form of unit nonresponse adjustment in sample surveys where entire questionnaires are missing due to noncontact or refusal to participate. A common approach computes the response weight as the inverse of the response rate within adjustment cells based on covariate information. In this paper, we consider the efficiency and robustness of nonresponse weight adjustment bated on the response propensity and predictive mean. In the simulation study based on 2000 Fishry Census in Korea, the root mean squared errors for assessing the various ways of forming nonresponse adjustment cell s are investigated. The simulation result suggest that the most important feature of variables for inclusion in weighting adjustment is that they are predictive of survey outcomes. Though useful, prediction of the propensity to response is a secondary. Also the result suggest that adjustment cells based on joint classification by the response propensity and predictor of the outcomes is productive.

• Survey Research
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• v.10 no.3
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• pp.21-36
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• 2009

This study suggests the applicability of web surveys regarding elections in order to contact a great number of young people. The propensity weighting model was estimated using the demographic variables and the covariate variables collected during the 2007 presidential election surveys. In order to adjust the internet survey to the telephone survey, we used the propensity score method. Propensity score weighting made the internet survey results closer to the telephone survey results. This shows that an internet survey with propensity weighting model is a potential alternative survey method in the prediction of elections.

• Journal of The Korean Association For Science Education
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• v.18 no.3
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• pp.415-425
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• 1998

The purpose of this study is to investigate the difference and relations in science related attitudes and science achievement in highschool students. Investigated differences between science related attitudes and science achievement and evaluated variations within city type, gender, grade level group. 404 high school students in Korea were sampled by cluster sampling method. Two instruments were used in this study. The ABC inventory(affection. behavioral intention. cognition scale of attitude toward science) was developed by the researcher(Lee, 1996, 1997). And MSAS(modified scientific attitude scale) has modified previous one. The major results are as follows: 1. Highschool students' Attitude toward Science is 3.24, 5-rating summative Likert scales. It showed slightly positive and favorable. 2. Highschool students' Scientific Attitude is 3.37, 5-rating summative Likert scales. It showed slightly positive tendencies of scientific attitude. 3. Findings indicated that middle' small city's students scored higher in Attitude toward Science and Scientific Attitude than metropolitan students. 4. The relationship between Attitude Toward Science and Scientific Attitude is 0.5716. The relationship between Scientific Attitude and Science Achievement is weaker than the relationship Attitude Toward Science and Science Achievement. 5. The results of three-way ANOVA indicated that were significant group differences(p<.05) in Attitude toward Science and Scientific Attitude. 6. After adjustment for the covariate(Scientific Attitude's score), statistically significant main effects of all group were found on the Attitude toward Science(p>.05). But after adjustment for the covariate(Attitude toward Science's score), statistically no significant main effects of all group were found on the Scientific Attitude(p>.05).

• Asian-Australasian Journal of Animal Sciences
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• v.30 no.6
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• pp.765-772
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• 2017

Objective: This study examines the genetic factors influencing the phenotypes (four economic traits:oleic acid [C18:1], monounsaturated fatty acids, carcass weight, and marbling score) of Hanwoo. Methods: To enhance the accuracy of the genetic analysis, the study proposes a new statistical model that excludes environmental factors. A statistically adjusted, analysis of covariance model of environmental and genetic factors was developed, and estimated environmental effects (covariate effects of age and effects of calving farms) were excluded from the model. Results: The accuracy was compared before and after adjustment. The accuracy of the best single nucleotide polymorphism (SNP) in C18:1 increased from 60.16% to 74.26%, and that of the two-factor interaction increased from 58.69% to 87.19%. Also, superior SNPs and SNP interactions were identified using the multifactor dimensionality reduction method in Table 1 to 4. Finally, high- and low-risk genotypes were compared based on their mean scores for each trait. Conclusion: The proposed method significantly improved the analysis accuracy and identified superior gene-gene interactions and genotypes for each of the four economic traits of Hanwoo.

• Journal of Korean Biological Nursing Science
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• v.20 no.3
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• pp.169-176
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• 2018

Purpose: This study was performed to elucidate whether the obesity or body image is a barrier to breast screening compliance in Korean women. Methods: We included 54,017 women aged between 35 to 70 years from the Korea Community Health Survey (KCHS) 2014 dataset. To identify whether a mutual relationship exists between weight perceptions and breast cancer screening rates, the participants were divided into three groups according to the level of concordance between Body Mass Index (BMI) and a subjective body image. Descriptive analyses, a chi-square test, and multivariate logistic regression analyses were performed. Results: After covariate adjustment, the screening rate of the overweight group was 1.09 times higher than the normal weight group (odds ratio [OR], 1.09; confidence interval [CI], 0.00-0.16; p= .038) and the severe obesity group was 1.20 times lower (OR, 0.83; CI, -0.36-0.00; p= .047). Weight misperception also had a significant influence on breast cancer screening. Especially, The overweight distortion group was less likely to undergo breast cancer screening (OR, 0.93; CI, -0.15-0.00; p= .037). Conclusion: Obesity and weight misperceptions are associated with lower compliance with breast cancer screening guidelines.

• Journal of Environmental Health Sciences
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• v.44 no.4
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• pp.380-390
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• 2018

Objective: A significant association between blood lead levels and hypertension has been reported in many studies. The relationship between cadmium and hypertension has been debated as well. We aimed to study the association of lead, cadmium, and both with hypertension in the Korean general population. Methods: We examined 5,967 adult men and 6,074 women who participated in the Korea National Health and Nutrition Examination Survey III-VI (2005, 2008-2013 years). Logistic regression models were used to examine the relationship between blood lead concentration and blood cadmium concentration and hypertension using logtransformed blood lead and cadmium concentrations as independent variables after covariate adjustment. Results: Adjusted for general characteristics, the odds ratio of log-lead to hypertension was 2.71 (1.82-4.03), and log-cadmium to hypertension was 2.52 (1.83-3.47). Estimates were found to be statistically significant (p<0.001). When a multiple logistic model was applied, the odds ratio of log-lead and log-cadmium for hypertension were 2.24 (1.50-3.36) and 2.24 (1.62-3.10), respectively. The standardized estimate coefficients of log-lead and logcadmium for hypertension were 4.77 and 6.65, respectively. Conclusion: We observed the association of blood lead concentration, blood cadmium concentration, and both with hypertension. This study suggests that exposure to lead and exposure to cadmium are both risk factors for hypertension.

• Asian Pacific Journal of Cancer Prevention
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• v.13 no.7
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• pp.3271-3274
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• 2012

Purpose : This study was performed to assess whether the weight status is associated with screening rates of breast and cervical cancer in Korean women. Methods: Study participants included women aged between 30 and 80 years from the 4th Korea National Health and Nutrition Examination Survey from 2007 to 2009. Body mass index was classified into ${\sim}18.4kg/m^2$ (underweight), $18.5{\sim}22.9kg/m^2$ (normal), $23{\sim}24.9kg/m^2$ (overweight), $25.0{\sim}29.9kg/m^2$ (moderate obesity) and $30.0kg/m^2$~ (severe obesity) according to the Asia Pacific Standards of WHO recommended definition of obesity. Screening rates of breast and cervical cancer were estimated by the recommendation of the National Cancer Screening Program of the National Cancer Center, Korea. Results : The overall screening rates for breast and cervical cancer were 51.3% and 50.1%, respectively. After covariate adjustment, the screening rates for breast cancer (adjusted odds ratio, 0.70; 95% confidence interval, 0.51 to 0.97) and cervical cancer (adjusted odds ratio, 0.71; 95% confidence interval, 0.53 to 0.94) were significantly lower in the women with severe obesity. Conclusion: Obesity is associated with lower compliance with breast and cervical cancer screening guidelines in Korean women.

• Journal of Korean Medical Science
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• v.33 no.44
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• pp.278.1-278.12
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• 2018

Background: We evaluated the association of blood pressure (BP) with blood levels of cadmium, lead, and cadmium and lead together (cadmium + lead) in a representative sample of adolescents from Korea. Methods: We used 2010-2016 data from the Korean National Health and Nutrition Examination Survey. This cross-sectional study enrolled adolescents aged at 10-18 years-old who completed a health examination survey and had blood measurements of lead and cadmium. The association of adjusted mean differences in diastolic and systolic BP with doubling of blood lead and cadmium were estimated by regression of BP against ${\log}_2$-transformed blood metals and their quartiles after covariate adjustment. Adjusted odds ratio for prehypertension were calculated for ${\log}_2$-transformed blood levels of lead and cadmium and their quartiles. Results: Our analysis of adolescents in Korea indicated that blood levels of lead and cadmium were not significantly associated with increased BP or risk of prehypertension. However, the cadmium + lead level was associated with prehypertension. Previous studies showed that blood levels of lead and cadmium were associated with increased BP and risk of hypertension in adult populations. We found no such association in Korean adolescents. Conclusion: We found that the cadmium + lead level was associated with prehypertension. The differences between adults and adolescents are because adolescents generally have lower levels of these blood metals or because adolescents only rarely have hypertension.