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

• English Language & Literature Teaching
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• v.16 no.1
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• pp.123-142
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• 2009

The present study used multi-faceted Rasch measurement to explore the characteristics and bias patterns of non-native raters when they scored L2 writing tasks. Three raters scored 254 writing tasks written by Korean university students on two topics adapted from the TOEFL Test of Written English (TWE). The written products were assessed using a five-category rating scale (Content, Organization, Language in Use, Grammar, and Mechanics). The raters only showed a difference in severity with regard to rating categories but not in task types. Overall, the raters scored Grammar most harshly and Organization most leniently. The results also indicated several bias patterns of ratings with regard to the rating categories and task types. In rater-task bias interactions, each rater showed recurring bias patterns in their rating between two writing tasks. Analysis of rater-category bias interaction showed that the three raters revealed biased patterns across all the rating categories though they were relatively consistent in their rating. The study has implications for the importance of rater training and task selection in L2 writing assessment.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.461-463
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• 1999

In this paper, we have systematically investigated the variation of electrical characteristics with back-gate bias of n-channel SOI MOSFET\\`s. When positive bias is applied back-gate surface is inverted and back channel current is increased. When negative bias is applied back-gate surface is accumulated but it does not affect to the electrical characteristics.

• Journal of Astronomy and Space Sciences
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• v.27 no.4
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• pp.367-375
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• 2010

In this study, we compared the precipitable water vapor (PWV) data derived from the radiosonde observation data at Sokcho Observatory and the PWV data at Sokcho Global Positioning System (GPS) Observatory provided by Korea Astronomy and Space Science Institute, from 0000 UTC, June 1, 2007 to 1200 UTC, May 31, 2009, and analyzed the radiosonde bias between the day and the night. In the scatter diagram of the daytime and nighttime radiosonde PWV data and the GPS PWV data, dry bias was found in the daytime radiosonde observation as known in the previous study. In addition, for all the rainfall events, the tendency that the wet bias of the radiosonde PWV increased as the GPS PWV decreased and the dry bias of the radiosonde PWV increased as the GPS PWV increased was significantly less distinctive in nighttime than in daytime. The quantitative analysis of the bias and error of the radiosonde PWV data showed that the mean bias decreased in the second year, regardless of nighttime or daytime rainfall, and the non-rainfall root mean square error (RMSE) was similar to that of the previous studies, while the rainfall RMSE was larger to a certain extent.

• Journal of Korean Ophthalmic Optics Society
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• v.9 no.2
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• pp.291-299
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• 2004

DLC films were deposited using the ECR-PECVD method with the fixed deposition condition, such as ECR power, methane and hydrogen gas-flow rates and deposition time, for various substrate bias voltage. We have investigated the ion bombardment effect induced by the substrate bias voltage on films during the deposition of film. The characteristic of the films were analyzed using the FTIR, Raman, and UV/Vis spectroscopy analysis shows that the amount of dehydrogenation in films was increased with the increase of substrate bias voltage and films thickness was decreased. Raman scattering analysis shows that integrated intensity ratio(ID/IG) of the D and G peak was increased as the substrate bias voltage increased and films hardness was increased. Optical transmittances of DLC film were decreased with increasing deposition time and substrate bias voltage. From these results, it can be concluded that films deposited at this experimental have the enhanced characteristics of DLC because of the ion bombardment effect on films during the deposition of film.

• Journal of the Korean Vacuum Society
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• v.9 no.4
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• pp.328-334
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• 2000

DLC (Diamond-Like Carbon) films were deposited by ECR-PECVD (electron cyclotron resonance plasma-enhanced chemical vapor deposition) method with the variation of substrate bias voltage under the others are constant except it. We have investigated the ion bombardment effect induced by the substrate bias voltage on films during the deposition of film. The characteristics of the film were analyzed using the Dektak surface profiler, SEM, FTIR spectroscopy, Raman spectroscopy and Nano Indentation tester. FTIR spectroscopy analysis shows that the amount of dehydrogenation in films was increased with the increase of substrate bias voltage and films thickness was decreased. Raman scattering analysis shows that integrated intensity ratio $(I_D /I_G)$ of the D and G peak was increased as the substrate bias voltage increased, and films hardness was increased. From these results, it can be concluded that films deposited at this experimental have the enhanced characteristics of DLC because of the ion bombardment effect on films during the deposition of film.

• Journal of Astronomy and Space Sciences
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• v.29 no.3
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• pp.295-303
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• 2012

In this study, we compared the precipitable water vapor (PWV) data derived from the radiosonde observation data at Sokcho Observatory and the PWV data at Sokcho Global Positioning System (GPS) Observatory provided by Korea Astronomy and Space Science Institute, for the years of 2006, 2008, 2010, and analyzed the radiosonde seasonal, diurnal bias according to radiosonde sensor types. In the scatter diagram of the daytime and nighttime radiosonde PWV data and the GPS PWV data, dry bias was found in the daytime radiosonde observation as known in the previous study. Overall, the tendency that the wet bias of the radiosonde PWV increased as the GPS PWV decreased and the dry bias of the radiosonde PWV increased as the GPS PWV increased. The quantitative analysis of the bias and error of the radiosonde PWV data showed that the mean bias decreased in the nighttime except for 2006 winter, and in comparison for summer, RS92-SGP sensor showed the highest quality.

• Journal of Institute of Control, Robotics and Systems
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• v.13 no.12
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• pp.1243-1251
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• 2007

In this paper a study on the simplified observability analysis of GPS/INS is introduced. Errors for the position, velocity, attitude, gyro and accelerometer biases, and lever arm between GPS antenna and inertial sensors are considered in the observablity analysis. From the error dynamics model in which relatively small terms are neglected, simple observability conditions are obtained such that the observability of GPS/INS is determined by the test on the attutude, gyro bias, and lever arm. Unobservable errors for the position, velocity, and accelerometer bias are determined by those for the attitude, gyro bias, and lever arm. The simplified observability conditions are applied to a constant speed horizontal motion. It is shown that there are seven unobservable modes for the motion including the vertical component of gyro bias. The analytic observability analysis results are confirmed with a covariance simulation.

• Journal of Preventive Medicine and Public Health
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• v.55 no.5
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• pp.424-427
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• 2022

A retrospective record-linkage study (RLS) based on medical records containing drug prescription histories involves immortal time bias (ITB). Thus, it is necessary to control for this bias in the research planning and analysis stages. Furthermore, a summary of a meta-analysis including RLSs that did not control for ITB showed that specific drugs had a preventive effect on the occurrence of the disease. Previous meta-analytic results of three systematic reviews evaluating the association between statin intake and gastric cancer risk showed that the summary hazard ratio (sHR) of the RLSs was lower than 1 and was statistically significant. We should consider the possibility of ITB in the sHR of RLSs and interpret the results carefully.

• Journal of the Korean institute of surface engineering
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• v.29 no.2
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• pp.93-99
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• 1996

In this work BN thin films were deposited on Si substrate by R. F. sputtering method at $200^{\circ}C$ and in Ar + $N_2$ mixed gas atmosphere. In order to investigate the effect of ion bombardment on substrate for c-BN bonding, substrate bias voltage was applied. The optimum substrate bias voltage for c-BN bonding was determined by FTIR analysis on specimens which were deposited with various bias voltages. Then BN thin film was deposited with this optimum condition and its phase, morphology, chemical composition, and refractive index were compared with those of BN film which was deposited without bias voltage. FTIR results showed that BN films deposited with substrate bias voltage were composed of mixed phases of c-BN and h-BN, while those deposited without bias voltage were h-BN only. When pure Ar gas was used for sputtering gas, BN films were delaminated easily from substrate in air, while when 10% $N_2$ gas was added to the sputtering gas, although c-BN specific infrared peak was reduced, delamination did not occur. GXRD and TEM results showed that BN films were amorphous phases regardless of substrate bias voltage, and AES results showed that the chemical compositions of B/N were about 1.7~1.8. The refractive index of BN film deposited with bias voltage was higher than that without bias voltage. The reason is believed to be the existence of c-BN bonding in BN film and the higher density of film that deposited with the substrate bias voltage.