• Communications for Statistical Applications and Methods
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• v.5 no.2
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• pp.391-401
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• 1998

유한모집단에서 표본을 추출할 때 표본으로 추출되는 경우의 수를 줄이거나 바람직하지 않은 표본들이 추출될 확률을 줄이기 위해서 관리적 선정 방법을 사용한다. 본 연구에서는 여러 가지 표본추출방법들을 관리적 선정에 적용하고 예를 통해서 그 효율성을 비교하였다.

• Communications for Statistical Applications and Methods
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• v.3 no.3
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• pp.299-302
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• 1996

표본조사에 있어서 층화추출법은 모집단에 관한 예비정보를 필요로 하고 있다. 조사자가 표본설계시 층화와 표본배분의 문제를 막연히 추상적으로 처리함으로 생기는 오류를 줄이기 위해서 다원적 입장에서 모집단에 대한 예비 정보를 정확하게 파악하고 이용해야 층화추출법의 효율을 올릴 수 있음을 지적하고 있다.

• The Korean Journal of Applied Statistics
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• v.22 no.2
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• pp.341-353
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• 2009

We consider sample-size determination problem motivated by comparative clinical trials where patient outcomes are characterized by a bivariate outcome of efficacy and safety. Thall and Cheng (1999) presented a sample size methodology for the case of bivariate binary outcomes. We propose a bivariate Wilcoxon-Mann-Whitney(WMW) statistics for sample-size determination for binary outcomes, and this nonparametric method can be equally used to determine sample sizes of ordinal outcomes. The two methods of sample size determination rely on the same testing strategy for the target parameters but differs in the test statistics, an asymptotic bivariate normal statistic of the transformed proportions in Thall and Cheng (1999) and nonparametric bivariate WMW statistic in the other method. Sample sizes are calculated for the two experimental oncology trials, described in Thall and Cheng (1999), and for the first trial example the sample sizes of a bivariate WMW statistic are smaller than those of Thall and Cheng (1999), while for the second trial example the reverse is true.

• Journal of the Korean Data and Information Science Society
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• v.27 no.5
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• pp.1317-1325
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• 2016

The purpose of this paper is to explain the factors affecting the wage of the vocational high school graduates. We particularly examine the effectiveness of controlling sample selection bias by employing the Tobit model and Heckman sample selection model. The major results are as follows. First it is shown that the Tobit model and Heckman sample selection model controlling sample selection bias is statistically significant. Hence all the independent variables seem to be statistically consistent with the theoretical model. Second, gender was statistically significant, both in the probability of employment and the wage. Third, the employment probability and wage of Maester high school graduates were shown to be high compared to all other graduates. Fourth, the higher parent's income, the higher are both the employment probability and the wage. Finally, parents education level, high school grade, satisfaction, and a number of licenses were found to be statistically significant, both in the probability of employment and wages.

• The Korean Journal of Applied Statistics
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• v.31 no.6
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• pp.733-749
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• 2018

Sample selection arises as a result of the partial observability of the outcome of interest in a study. Heckman introduced a sample selection model to analyze such data and proposed a full maximum likelihood estimation method under the assumption of normality. Recently sample selection models for binomial and Poisson response variables have been proposed. Based on the theory of symmetry-modulated distribution, we extend these to a model for overdispersed count data. This type of data with no sample selection is often modeled using negative binomial distribution. Hence we propose a sample selection model for overdispersed count data using the negative binomial distribution. A real data application is employed. Simulation studies reveal that our estimation method based on profile log-likelihood is stable.

• The Korean Journal of Applied Statistics
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• v.18 no.1
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• pp.197-210
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• 2005

In Korea, mathematics education has been taken according to the 7th national mathematics curriculum renovated by the Ministry of Education and Human Resources Development announcement in 1997. The education of probability and Statistics has been carried out as a part of this curriculum. We analyze and compare mathematics 1 textbooks for 11-12 grade students. Descriptions of random variable, sample variance and sample standard deviation, distribution of sample mean, and etc. which are on some textbooks, are misleaded in school education. We suggest the unbiased estimator of sample variance in accordance with textbooks and central limit theorem of sample mean under normal population.

• The Korean Journal of Applied Statistics
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• v.22 no.6
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• pp.1301-1313
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• 2009

Efficiency and sensitivity of BLS adjustment method have been studied and the method is known to provide more accurate estimate of total by using properly adjusted weights of samples. However, BLS methods provide different efficiencies according to the magnitudes of correlation coefficients and the sizes of samples in strata. In this paper we study the efficiency of the BLS adjustment according to the sample sizes and correlations in strata. For this study, 2007 monthly labor survey data is used.

• Proceedings of the Korean Statistical Society Conference
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• 2004.11a
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• pp.29-34
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• 2004

계속 반복하여 실시되는 통계조사에서 조사원은 오차를 발생시키는 주요 요인으로 간주되고 있다 조사원에 의한 오차를 측정하는 방법으로서 조사표 형태별로 조사원, 집락 및 가구 등 변수에 따라 할당하고 선계방법에 따른 추정 값에 대한 효과 및 효과의 분산을 산출하는 모델을 제시한다. 또한 실제 조사모델로부터 품질관리표본을 추출하여 이를 대상으로 리인터뷰를 실시한 결과를 조사원의 인구통계학적 특성별로 분석하고 불일치지수 등을 산출함으로써 오차를 분석하는 방법을 제시한다.

• The Korean Journal of Applied Statistics
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• v.18 no.3
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• pp.689-699
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• 2005

We usually use $S^2=\frac{{\Sigma}^n_{i=1}(X_i-\={X})^2}{n-1}$ as sample variance. Korean high school text-books use $S^2_n=\frac{{\Sigma}^n_{i=1}(X_i-\={X})^2}{n}$as sample variance. We can compare the above two definitions of sample variance through their theoretical relationship and simulation.

• Journal of the Korean Data and Information Science Society
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• v.11 no.1
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• pp.83-90
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• 2000

The chi-squared test statistic is usually employed for testing independence of two categorical variables in a two-way contingency table. It is well known that, under independence, the test statistic has an asymptotic chi-squared distribution under multinomial or product-multinomial models. For the case where both margins fixed, the sampling model of the contingency table is a multiple hypergeometric distribution and the chi-squared test statistic follows the same limiting distribution. In this paper, we study the difference between the small sample and large sample distributions of the chi-squared test statistic for the case with fixed margins. For a few small sample cases, the exact small sample distribution of the test statistic is directly computed. For a few large sample sizes, the small sample distribution of the statistic is generated via a Monte Carlo algorithm, and then is compared with the large sample distribution via chi-squared probability plots and Kolmogorov-Smirnov tests.