• Tunnel and Underground Space
• /
• v.13 no.5
• /
• pp.344-352
• /
• 2003

The procedures to correct sampling biases for discontinuity data obtained from 1D survey line(borehole or scanline) is addressed. The Probability of intersection between the survey line and a circular discontinuity is considered, and a correction far orientation bias is developed assuming discontinuities as equivalent circular disks. The correction incorporates the effect of the angle between the direction of survey line and each discontinuity plane belonging to the discontinuity cluster, size of each discontinuity and length of the survey line. A procedure is provided to estimate unbiased discontinuity spacing parameters using the discontinuity spacing data based on the measurements carried out on a finite length of the survey line.

• Proceedings of the KSEG Conference
• /
• 2003.04a
• /
• pp.27-35
• /
• 2003

시추공에서 측정된 절리자료의 샘플링 편향오류를 보정하는 절차를 기술하였다. 시추공에서 절리의 방향이 관측될 수 있는 확률은 시추공에 대한 절리의 상대적인 방향 이외에도 절리의 크기, 절리의 모양 및 시추공의 반경 과 길이와 같은 요인에 의하여 결정될 수 있으며, 이러한 요인들에 의하여 나타날 수 있는 절리자료의 방향편향을 보정할 수 있는 방법론을 제시하였다 유한 길이의 시추공으로부터 산정된 절리의 간격분포는 샘플링 영역인 시추공 길이의 영향에 의한 산정치의 오류를 내포하고 있으며, 이에 대한 보정법을 고찰하였다.

• The Korean Journal of Applied Statistics
• /
• v.33 no.4
• /
• pp.409-420
• /
• 2020

In business survey, modified cut-off sampling is commonly used to greatly increase the accuracy of the estimation while reducing the number of samples. However, non-response rate of take-all stratum has increased significantly and the sample substitution is not possible because the non-response in the take-all stratum affects the accuracy of the estimation. It is important to adjust the bias appropriately if non-response is affected by the variable of interest. In this study, a bias adjusted estimation is proposed as an appropriate method to deal with a non-response in the take-all stratum. In particular, the estimator proposed by Chung and Shin (2020) was applied to the bias adjustment for the take-all stratum; therefore, we suggest a new method to adjust properly for the take-all stratum. The superiority of the proposed estimator was examined through simulation studies and confirmed through actual data analysis.

• The Korean Journal of Applied Statistics
• /
• v.33 no.4
• /
• pp.439-449
• /
• 2020

Meta-analysis provides a way of integrating several independent studies of interest. Since small studies with statistically significant results are more likely to be published, publication bias, which is a special case of selection bias, often occurs in meta analysis. Conditional likelihood and weighted estimating equation have been proposed to deal with publication bias, but they require to specify a correct selection probability model. In contrast, the pairwise pseudolikelihood approach can correct publication bias without fully specifying the correct selection probability model, but its performance in meta-analysis was not investigated. In this paper, we perform a numerical study about whether the pairwise pseudolikelihood approach is effective for solving publication bias arising from typical meta-analysis settings.

• Survey Research
• /
• v.10 no.1
• /
• pp.169-186
• /
• 2009

The propensity score method is used to minimize the bias level in social survey, which comes from nonresponse. The theoretical concept and the background of the propensity score method is discussed first. The propensity score method was first applied in the epidemiology observational study. I have summarized the process of the three propensity score methods that were used to reduce estimation bias in this study. Matching by propensity score is applied to the relatively large control group. Subclassification has the advantage of using whole control group data and regression adjustment is applied to multiple covariates as well as propensity score of each unit is computable and usable. Lastly, the application procedures of propensity score method to reduce the nonresponse bias is suggested and its applicability to real situation is reviewed with the existing data.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.11a
• /
• pp.404-407
• /
• 2011

The fluidic thrust vector control using co-flowing coanda effect of secondary jet at the nozzle exit is a new concept for efficient thrust vectoring of supersonic jet exhausts. Flow visualization of the flow fields in previous studies have shown some pros and cons of the technique, however, most of the observations were somewhat limited as qualitative data. The present study was designed to evaluate the quantitative performance-characteristics of the thrust-vectoring technique utilizing coanda effects of the secondary jet. Details of design of the test device and calibration/data reduction procedure are provided.

• The Korean Journal of Applied Statistics
• /
• v.34 no.6
• /
• pp.923-936
• /
• 2021

A large number of non-responses are occurring in the sample survey, and various methods have been developed to deal with them appropriately. In particular, the bias caused by non-ignorable non-response greatly reduces the accuracy of estimation and makes non-response processing difficult. Recently, Chung and Shin (2017, 2020) proposed an estimator that improves the accuracy of estimation using parametric super-population model and response rate model. In this study, we suggested a bias corrected non-response mean estimator using a nonparametric function generalizing the form of a parametric super-population model. We confirmed the superiority of the proposed estimator through simulation studies.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.41 no.2
• /
• pp.142-149
• /
• 2013

The thrust vector control technique is essential for high maneuverability of unmanned aerial vehicles. In the present study, a multi-component balance was developed to quantitatively evaluate the thrust-vectoring performance of a supersonic rectangular nozzle based on the Coanda coflowing effect. Precise calibration and detailed data analysis were performed during the development. It was found that the cross-talk errors between load cells in the balance were less than 5%, and that the unwanted errors due to high-pressure supply tubes were almost negligible, which contributed to the high accuracy of the present balance design. Some preliminary test results of the thrust-vectoring performance of the present nozzle design were also obtained and analyzed.

• The Korean Journal of Applied Statistics
• /
• v.33 no.1
• /
• pp.11-23
• /
• 2020

Sampling design should provide statistics to meet a given accuracy while saving cost and time. However, a large number of non-responses are occurring due to the deterioration of survey circumstances, which significantly reduces the accuracy of the survey results. Non-responses occur for a variety of reasons. Chung and Shin (2017, 2019) and Min and Shin (2018) found that the accuracy of estimation is improved by removing the bias caused by non-response when the response rate is an exponential or linear function of variable of interests. For that case they assumed that the error of the super population model follows normal distribution. In this study, we proposed a non-response bias adjusted estimator in the case where the error of a super population model follows the gamma distribution or the log-normal distribution in a business survey. We confirmed the superiority of the proposed estimator through simulation studies.

• Proceedings of the Korean Institute of Intelligent Systems Conference
• /
• 1998.10a
• /
• pp.218-224
• /
• 1998

본 논문에서는 컬러 모니터용 전자관(CDT; Color Display Tube)의 편향 요크(DY; Deflection Yoke)의 제조 공정상 오차가 발생시키는 컨버전스의 오차를 보정하기 위하여 붙이는 페라이트 박판(Ferrite Sheet)의 위치를 결정하는 규칙을 생성하는 박판을 붙여야 하는지 판단한다. 이를 러프 집합 이론을 이용하여 컨버전스 값을 조건부 속성으로, 페라이트 박판의 위치를 판단부 속성으로 하여 판단 테이블을 만들고 이때 발생하는 몇 가지 문제를 해결하여 최소화된 규칙을 찾아내는 방안을 제안한다.