• Journal of The Korean Astronomical Society
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• v.40 no.4
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• pp.99-106
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• 2007

Statistical analyses were performed to investigate the relative success and accuracy of daily maximum X-ray flux (MXF) predictions, using both multilinear regression and autoregressive time-series prediction methods. As input data for this work, we used 14 solar activity parameters recorded over the prior 2 year period (1989-1990) during the solar maximum of cycle 22. We applied the multilinear regression method to the following three groups: all 14 variables (G1), the 2 so-called 'cause' variables (sunspot complexity and sunspot group area) showing the highest correlations with MXF (G2), and the 2 'effect' variables (previous day MXF and the number of flares stronger than C4 class) showing the highest correlations with MXF (G3). For the advanced three days forecast, we applied the autoregressive timeseries method to the MXF data (GT). We compared the statistical results of these groups for 1991 data, using several statistical measures obtained from a $2{\times}2$ contingency table for forecasted versus observed events. As a result, we found that the statistical results of G1 and G3 are nearly the same each other and the 'effect' variables (G3) are more reliable predictors than the 'cause' variables. It is also found that while the statistical results of GT are a little worse than those of G1 for relatively weak flares, they are comparable to each other for strong flares. In general, all statistical measures show good predictions from all groups, provided that the flares are weaker than about M5 class; stronger flares rapidly become difficult to predict well, which is probably due to statistical inaccuracies arising from their rarity. Our statistical results of all flares except for the X-class flares were confirmed by Yates' $X^2$ statistical significance tests, at the 99% confidence level. Based on our model testing, we recommend a practical strategy for solar X-ray flare predictions.

• The Korean Journal of Applied Statistics
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• v.22 no.2
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• pp.355-364
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• 2009

A simple method is proposed for constructing nonparametric confidence intervals for the difference or ratio of two median failure times. The method applies when clustered survival data with censoring is randomized either (I) under cluster randomization or (II) subunit randomization. This method is simple to calculate and is based on non-parametric density estimation. The proposed method is illustrated with the otology study data and HL-A antigen study data. Moreover, the simulation results are reported for practical sample sizes.

• The Korean Journal of Applied Statistics
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• v.22 no.1
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• pp.205-220
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• 2009

For modeling skewed semicircular data, we derive new family of the exponential distributions. We extend it to the l-axial exponential distribution by a transformation for modeling any arc of arbitrary length. It is straightforward to generate samples from the f-axial exponential distribution. Asymptotic result reveals two things. The first is that linear exponential distribution can be used to approximate the l-axial exponential distribution. The second is that the l-axial exponential distribution has the asymptotic memoryless property though it doesn't have strict memoryless property. Some trigonometric moments are also derived in closed forms. Maximum likelihood estimation is adopted to estimate model parameters. Some hypotheses tests and confidence intervals are also developed. The Kolmogorov-Smirnov test is adopted for goodness of fit test of the l-axial exponential distribution. We finally obtain a bivariate version of two kinds of the l-axial exponential distributions.

• Proceedings of the Safety Management and Science Conference
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• 2006.04a
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• pp.447-470
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• 2006

According to Granger causality test, yield of Cooperate Bond and export amount of Machinery have a meaning at statistical Confidence level of 10%. In case of index of the unit cost of export and export amount of Machinery, they have an interactive Granger cause. In yen dollar exchange rate and export amount of Machinery, former variable gives an unilateral Granger cause to latter that. Also, call rate gives an unilateral Granger cause to export amount of Machinery. In case of $M_3$ & export amount of Machinery, former variable have an influence on latter that at 5% Confidence level.

• The Korean Journal of Applied Statistics
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• v.25 no.3
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• pp.435-446
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• 2012

Epidemiologic studies frequently try to estimate the impact of a specific risk factor. The risk difference and the risk ratio are generally useful measurements for this purpose. When using such measurements for rare events, the standard approaches based on the normal approximation may fail, in particular when no events are observed. In this paper, we discuss and evaluate several existing methods to construct confidence intervals around risk differences and risk ratios using Monte-Carlo simulations when the disease of interest is rare. The results in this paper provide guidance how to construct interval estimates of the risk differences and the risk ratios when no events are detected.

• The Research Journal of the Costume Culture
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• v.16 no.4
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• pp.709-721
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• 2008

The purpose of this study is to identify different consumer clusters based on clothing involvement and to examine the differences in consumer characteristics related to clothing purchasing. As consumer behavior characteristics, this study included visiting purpose of Internet shopping malls, purchasing situation, consumer confidence, and clothing satisfaction. Data were gathered by surveying university students living in Seoul metropolitan area using convenience sampling, and 321 questionnaires were used in the statistical analysis. In analyzing data, cluster analysis and one-way ANOVA were conducted. The cluster analysis identified four different consumer clusters, and there were significant differences in the consumer behavior characteristics among the four clothing involvement clusters.

• English Language & Literature Teaching
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• v.18 no.2
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• pp.149-170
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• 2012

The purpose of the present study is to examine the degree to which the writing instruction using animations has effects on the writing performance of $4^{th}$ year elementary school students. This study also examined the effects of the animation-based writing instruction on the interest and confidence of those students. To this aim, the present study utilized a set of writing tests and questionnaires before and after the instruction. The data were collected from 63 elementary school students. The data were then analyzed using a series of statistical analyses. The results suggested that the students who received the writing instruction using animations performed significantly better on the writing test than those who received the textbook-based instruction. The results also suggested that those who received the animation-based instruction showed more positive interest and confidence on English and English learning. Finally, limitations of the present study and suggestions for further studies are discussed at the end of the paper.

• Journal of The Korean Astronomical Society
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• v.21 no.2
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• pp.133-153
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• 1988

Linear polarization has been measured for fifteen extragalactic radio sources in the field of supernova remnant S 147. These observations were made at 4885, 4835, 1665, 1515, 1465, and 1385 MHz using the Very Large Array, primarily to determine unambiguous Rotation Measures (RM) of the sources. This yields a total of 11 new RM sources. Comparisons of a sample of sources which are seen through S 147 were made with sources located farther away. The result tentatively indicates that the distribution of the rotation measure of the former population is broadened, with more than a 85% level of confidence. This constitutes evidence that there is a SNR contribution to rotation measure in sources seen through the SNR. Limits on this RM contribution are statistically at 30 < | RM | < 70 rad $m^{-2}$ with a 85% statistical level of confidence. These result imply the magnetic field in the rim of S 147 has strength 10 microguass if the electron density is $1\;cm^{-3}$.

• Journal of the Korean Data and Information Science Society
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• v.15 no.4
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• pp.973-980
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• 2004

Phase I clinical trials are often pharmacologically oriented and usually attempt to find the best dose of drug to employ. However, other purposes like determination of sizes and types of side effects and toxicity and organ system involved are equally important. Estimation of treatment effects or side effects is usually ignored since it is usually based on too small sample, even though Phase II clinical trials would be designed based on the Phase I studies. Statistical methods for constructing the approximate confidence interval for population median in case of small sample are considered and an improved method is proposed. The proposed estimator is compared with current methods through simulation studies.

• The Korean Journal of Applied Statistics
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• v.20 no.1
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• pp.159-165
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• 2007

The statistics chapter in High School Mathematics I as implemented in The 7th Curriculum is reviewed critically. In views from mathematical integrity or logic, the current contents are not satisfactory in several key issues. Specific instances are the law of large numbers, normal distribution and confidence intervals for population mean. We suggest alternative teaching points to handle such difficulties and propose re-structuring the course syllabus with reduced items.