• Communications for Statistical Applications and Methods
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• 제23권4호
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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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• 제26권1호
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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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• 제16권1호
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• pp.103-113
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• 2009

표본조사에서 무응답은 비 표본추출오차를 발생시키는 중요한 원인 중 하나이다. 단위무응답이 발생하는 경우 무응답에 의한 편향을 줄이는 동시에 추정의 정도를 향상시키기 위해 단위무응답 조정층을 구성해 무응답 가중치 조정을 하는 것이 일반적이다. 본 연구에서는 무응답 조정층 구성과 관련된 기존의 이론들을 정리하고 어업총조사 자료를 이용한 실증적인 모의실험을 통해 효과적으로 무응답 조정층을 구성하는 방안에 대해 살펴본다. 모의실험결과 응답성향에 따른 조정층 구성보다는 예측평균을 기준으로 한 조정층 구성이 효율성 측면에서 효과적인 것으로 나타났으며, 아울러 다른 관심변수에도 적용될 수 있는 로버스트한 조정층 구성을 위해서는 예측평균만을 고려하는 것보다 응답성향과 예측평균을 모두 고려한 조정층 구성방법이 효과적인 것으로 나타났다. 한편 무응답 조정을 위한 응답률 산출에 있어서 설계가중치의 적용 필요성에 대해 살펴본 결과 설계가중치 적용 여부는 추정결과에 거의 영향을 주지 않는다는 사실을 확인할 수 있었다.

• 한국조사연구학회지:조사연구
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• 제10권3호
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• pp.21-36
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• 2009

본 연구에서는 선거여론조사에서 좀더 많은 젊은 유권자를 접촉하기 위해서 인터넷조사의 적용 가능성을 제시하고자 한다. 2007년 대선여론조사에서 수집한 인구통계학 변수와 공변량 변수를 이용하여 성향점수모형을 추정하였다. 인터넷조사에서 투표성향을 전화조사의 것과 같이 보정하기 위해서 추정한 성향점수모형을 사용하였다. 실제로 인터넷조사 데이터에 성향점수 가중치를 적용함으로써 전화조사의 추정치에 근접하게 됨을 보였다. 성향가중모형을 인터넷조사의 데이터에 적용하여 인터넷조사데이터만으로 전화조사와 유사한 추정치를 얻을 수 있음을 예시함으로써 선거여론조사에서 전화조사의 대안적인 조사방법으로 인터넷조사의 활용가능성을 실제 조사데이터로 입증하였다는 데 그 의의가 있다.

• 한국과학교육학회지
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• 제18권3호
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• pp.415-425
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• 1998

이 연구의 목적은 고등학생의 과학에 관련된 태도와 과학 성취도간의 관계와 차이를 알아 보기 위한 것이다. 과학에 관련된 태도와 과학 성취도간의 관계와 차이가 성별, 지역별, 학년별로 조사되었다. 404명의 학생들이 군집 표집에 의해 조사되었다. 본 연구의 조사를 위하여 2개의 도구가 사용되었는데, 하나는 이경훈(1996, 1997)이 개발한 과학에 대한 태도의 ABC 척도와 수정과 학적태도척도(MSAS) 이다. 1. 고등학생의 과학에 대한 태도는 5단계 평정 척도로 3.24로 중립적인 경향에서 약간 긍정적인 방향으로 나타났다. 2. 고등학생의 과학적 태도는 5단계 평정 척도로 3.37로 중립적인 경향에서 긍정적인 방향으로 위치하고 있으며, 개방성>비판성>판단유보>객관성>정직성의 순으로 나타났다. 3. 과학에 대한 태도는 대도시보다 중소 규모의 도시에서 높게 나타나고 있으며, 학년이 증가할수록 감소하고 있다. 그리고 여학생보다 남학생들의 과학에 대한 태도가 높은 것으로 나타났다. 과학적 태도 역시 대도시보다 중소 규모의 도시에서 높게 나타나고 있으며, 학년이 증가할수록 감소하고 있다. 그러나 여학생과 남학생틀의 과학적 태도는 차이가 나타나지 않았다. 4. 과학에 대한 태도와 과학적 태도는 0.5716 의 높은 상관을 보이는 반면에 과학에 대한 태도와 과학 성취도는 0.2940으로 나타났으며, 과학적 태도와 과학 성취도의 상관은 그보다 낮은 0.2340 올 나타냈다. 5. 조사 집단의 도시 유형별, 학년별, 성별에 따른 과학에 대한 태도와 과학적 태도의 차이를 알아 보기위해 변량분석(ANOVA)을 한 결과 집단간의 과학에 대한 태도와 과학적 태도의 차이가 있는 것으로 나타났다. 6. 집단별로 과학적 태도를 통제한 후 과학에 대한 태도의 차이를 알아 본 결과 집단간의 과학에 대한 태도의 차이가 있는 것으로 나타났으나, 과학에 대한 태도를 통제하고 과학적 태도의 차이를 알아 본 결과 집단간 차이가 없는 것으로 나타났다.

• Asian-Australasian Journal of Animal Sciences
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• 제30권6호
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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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• 제20권3호
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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.

• 한국환경보건학회지
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• 제44권4호
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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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• 제13권7호
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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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• 제33권44호
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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.