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통계모형을 이용하여 모의실험 결과 분석하기에 대한 보완연구
Bongseong Kim,김지현 한국통계학회 2022 응용통계연구 Vol.35 No.4
비모수적 추정량의 성능을 이론적으로 비교하기 힘들 때 흔히 모의실험을 실시한다. 다양한 실험조건에서 여러 추정량에 대해 얻어진 모의실험 결과를 회귀모형을 이용해 분석하면보다 체계적이고 정확한 비교를 할 수 있다는 것을 Kim과 Kim (2021)에서 보였다. 이 연구는 Kim과 Kim (2021)에 대한 후속연구이자 보완연구이다. 회귀모형의 오차항에 대한 분산공분산행렬에서 이분산성만 고려하고 공분산을 선행연구에서 무시했는데, 공분산을 고려하게 되면 분산공분산행렬은 블록대각행렬이 된다. 본 연구에서 블록대각행렬인 분산공분산행렬을 추정하여 분석에 이용하는 방법을 제시하였다. 이렇게 하면 명목신뢰수준을 보장하면서 유의하게 성능 차이가 나는 추정량 짝을 더 잘 찾을 수 있다는 것도 보였다.
Kim Kihyun,Bang Woo-Dae,Han Kyungdo,Kim Bongseong,Lee Jung Myung,Chung Hyemoon 한국지질동맥경화학회 2021 지질·동맥경화학회지 Vol.10 No.3
Objective: We compared the effects of high-intensity statin monotherapy versus moderateintensity statin and ezetimibe combination therapy on major adverse cardiovascular events (MACE) in patients with acute myocardial infarction (AMI). Methods: Using the Korean National Health Insurance Service database, we screened 82,941 patients with AMI who underwent percutaneous coronary intervention (PCI) between 2013 and 2016. Among them, we identified 9,908 patients treated with atorvastatin 40 mg (A40, n=4,041), atorvastatin 20 mg + ezetimibe 10 mg (A20+E10, n=233), rosuvastatin 20 mg (R20, n=5,251), or rosuvastatin 10 mg + ezetimibe 10 mg (R10+E10, n=383). The primary outcome was MACE, a composite of all-cause death, non-fatal myocardial infarction undergoing PCI, repeat revascularization, and ischemic stroke. Multivariable analyses were performed using the inverse probability of treatment weighting method. Results: The incidence rate of MACE in the overall population was 42.97 cases per 1,000 person-years. There was no significant difference in the risk of composite outcomes of MACE between the groups. However, the R10+E10 group showed a higher risk of all-cause death (hazard ratio, 2.07; 95% confidence interval, 1.08–3.94) than the A40 group (reference group) in the weighted multivariable model. Conclusions: In this study, there was no significant difference in the composite outcome of MACE between high-intensity statin monotherapy and moderate-intensity statin and ezetimibe combination therapy.
Estimating causal effect of multi-valued treatment from observational survival data
Kim, Bongseong,Kim, Ji-Hyun The Korean Statistical Society 2020 Communications for statistical applications and me Vol.27 No.6
In survival analysis of observational data, the inverse probability weighting method and the Cox proportional hazards model are widely used when estimating the causal effects of multiple-valued treatment. In this paper, the two kinds of weights have been examined in the inverse probability weighting method. We explain the reason why the stabilized weight is more appropriate when an inverse probability weighting method using the generalized propensity score is applied. We also emphasize that a marginal hazard ratio and the conditional hazard ratio should be distinguished when defining the hazard ratio as a treatment effect under the Cox proportional hazards model. A simulation study based on real data is conducted to provide concrete numerical evidence.
펄스 모듈레이터용 정전 유도 사이리스터의 최적 게이트 드라이버 설계 및 성능 측정
김봉석(Bongseong Kim),고광철(Kwang-Cheol Ko) 대한전기학회 2006 대한전기학회 학술대회 논문집 Vol.2006 No.10
SI-Thyristor는 기존의 Power semiconductor인 단일 IGBT, MOSFET과 비교하여 높은 정격 전압과 대전류의 소호가 가능하며 빠른 tum on swithcing time을 가지는 특성이 있다. 하지만 게이트 드라이버를 이용한 SI-Thyristor의 tum on 구동시에는 전압구동의 특성과 tum off시에는 전류 구동의 특성에 가까운 구동 특성이 요구되기 때문에 스위칭 요구 특성에 맞는 게이트 드라이버의 설계 및 제어가 쉽지 않다. 본 논문은 펄스 파워 어플리케이션으로 SI-Thyristor(PT-201 5㎸/100A)를 사용하여 pulsed power modulator용 SI-Thyristor의 게이트 드라이버의 요구인 빠른 tum on switching 특성과 tum off 시 Si-Thyristor 내의 전하를 빨리 제거하기 위한 조건을 제시하고 있다.
김봉석(Bongseong Kim),고광철(Kwang-Cheol Ko) 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.7
상압에서의 유전장벽방전(DBD: Dielectric Barrier Discharing) 방법은 현재 높은 효율성과 공정의 편이성으로 인하여 높은 진공도를 요구하는 반도체 공정 단계 및 광원 또는 오존 발생 장치로 각광받고 있다. 하지만, 기존의 플라즈마 진단 방법 및 분석 방법을 통하여 특성 부하 목적으로 사용되는 유전장벽 방전의 특성을 파악하는 것은 한계가 있다. 본 논문은 오존 발생용 평판형 DBD 반응기 및 전원 장치를 전기 모델링하여 평판형 DBD 반응기의 변화 및 전원 장치의 최적 조건을 판별하는 것을 목적으로 하고 있다.
( Eun Hui Bae ),( Sang Yup Lim ),( Bongseong Kim ),( Kyung-do Han ),( Tae Ryom Oh ),( Hong Sang Choi ),( Chang Seong Kim ),( Seong Kwon Ma ),( Soo Wan Kim ) 대한신장학회 2021 Kidney Research and Clinical Practice Vol.40 No.3
Background: Hypertension is the most important modifiable risk factor for mortality and morbidity in chronic kidney disease and cor-onary artery syndrome. The effect of hypertension prior to percutaneous coronary intervention (PCI) on the development of end-stage renal disease (ESRD) is unknown. Methods: We used nationally representative data from the Korean National Health Insurance System―140,164 subjects were en-rolled during 2010-2015; they were free of ESRD at enrolment, underwent PCI, and were followed up until 2017. Blood pressure (BP) was measured within at least 2 years prior to PCI. The primary outcome was the development of ESRD. Results: During a median follow-up of 5.4 years, 2,082 participants (1.5%) developed ESRD. The highest systolic BP group (>160 mmHg) showed a higher hazard ratio (3.69; 95% confidence interval, 2.61-5.23) than the reference group (110-119 mmHg). Simi-lar results were observed in the highest diastolic BP group (>120 mmHg), which showed a higher hazard ratio than the reference group (70-79 mmHg). However, ESRD risk showed a J-shaped relationship with baseline systolic and diastolic BP at 113 and 74 mmHg in diabetes mellitus subgroup, respectively, after adjustment for potential confounders. Conclusion: Our study showed that a high systolic or diastolic BP prior to PCI was independently associated with an increased inci-dence of ESRD.
( Eun Hui Bae ),( Sang Yup Lim ),( Eun Mi Yang ),( Tae Ryom Oh ),( Hong Sang Choi ),( Chang Seong Kim ),( Seong Kwon Ma ),( Bongseong Kim ),( Kyung-do Han ),( Soo Wan Kim ) 대한신장학회 2023 Kidney Research and Clinical Practice Vol.42 No.2
Background: Although multiple factors influence the risk of major adverse cardiovascular events (MACE), the effects of socioeconomic status on MACE in the presence and absence of renal dysfunction (RD) have not been comprehensively explored in Korea. Methods: We examined the effects of socioeconomic status on MACE in individuals with and without RD. The data of 44,473 Koreans from 2008 to 2017 were obtained from the Health Care Big Data Platform of the Ministry of Health and Welfare in Korea. Their socioeconomic status was assessed using a socioeconomic score (SES) based on marital status, education, household income, and occupation. The incidence of myocardial infarction (MI), stroke, and death was compared according to SES level (0-4). Multiple linear regression analysis was used to evaluate the hazard ratios and 95% confidence intervals for outcomes based on participant SES. Results: MI risk was only affected by education level. The participants’ income, education, and SES affected their stroke risk, whereas death was associated with all four socioeconomic factors. The incidence of stroke and death increased as SES worsened (from 0 to 4). SES was positively related to risk of stroke and death in participants without RD. SES did not affect MI, stroke, or death in participants with RD. Conclusion: A low socioeconomic status is associated with risk of stroke and death, especially in individuals without RD.
최홍상,Kim Bongseong,Han Kyungdo,오태렴,서상헌,김민아,김창성,배은희,마성권,김수완 대한신장학회 2023 Kidney Research and Clinical Practice Vol.42 No.1
Background: Several studies have reported that depression is prevalent in patients with diabetes or chronic kidney disease. However,the relationship between weight changes and the risk of depression has not been elucidated in patients with diabetic kidney disease(DKD).Methods: From the Korean National Health Insurance Service database, we selected 67,866 patients with DKD and body weightdata from two consecutive health examinations with a 2-year interval between 2009 and 2012. Weight change over 2 years was categorizedinto five groups: ≥–10%, <–10% to ≥–5%, <–5% to <5%, ≥5% to <10%, and ≥10%. The occurrence of depression was monitoredvia the codes of International Statistical Classification of Diseases, 10th revision through the end of 2018.Results: During the 5.24-year follow-up, 17,023 patients with DKD developed depression. Weight change and the risk of depressionhad a U-shaped relationship: patients with ≥–10% weight change (hazard ratio [HR], 1.12) and those with ≥10% weight change (HR,1.11) showed higher HRs for depression than those with <–5% to <5% weight change, even after adjusting for several confoundingfactors. In the subgroup analyses, the risk of depression tended to increase as weight gain or weight loss increased in all subgroups.Conclusion: Both weight loss and weight gain increased the risk of depression in patients with DKD.