• 응용통계연구
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• 제25권4호
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• pp.621-632
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• 2012

Recurrent event data can be easily found in longitudinal studies such as clinical trials, reliability fields, and the social sciences; however, there are a few observations that disappear temporarily in sight during the follow-up and then suddenly reappear without notice like the Young Traffic Offenders Program(YTOP) data collected by Farmer et al. (2000). In this article we focused on inference for a cumulative mean function of the recurrent event data with these incomplete observation gaps. Defining a corresponding risk set would be easily accomplished if we know the exact intervals where the observation gaps occur. However, when they are incomplete (if their starting times are known but their terminating times are unknown) we need to estimate a distribution function for the terminating times of the observation gaps. To accomplish this, we treated them as interval-censored and then estimated their distribution using the EM algorithm proposed by Turnbull (1976). We proposed a nonparametric estimator for the cumulative mean function and also a nonparametric test to compare the cumulative mean functions of two groups. Through simulation we investigated the finite-sample performance of the proposed estimator and proposed test. Finally, we applied the proposed methods to YTOP data.

• 한국식품위생안전성학회지
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• 제16권1호
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• pp.21-26
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• 2001

유기인계 농약은 주로 수확률을 증가시킬 목적으로 과일, 채소, 곡류를 포함한 농산물에 사용하는 살충제로, 최근의 위해성평가기술은 독성기전이 동일한 물직들에 대해서 기준이 되는 물질의 특성을 1로하여 상대독성계수를 고려하므로 동시노출평가(cumulative risk assessment)를 수행하고 있다. 본 연구에서는 식품섭취를 통한 유기인계 농약의 동시다중노출에 기인된 위해정도를 판단하기 위하여 유기인계 농약과 다소비노출가능식품 등을 대상으로 cumulative risk assessment 를 실시코자 하였다. 펑가에 고려된 농약은 우리나라에서 사용빈도가 높은 농약(Acephate, Azinphos-methyl, Chlorpyrifos, Diazinon, Dimethoate, Ethion, Malathion, Methamidophos, Methidathion, Parathion-methyl, Phosmet, Pirimiphos-methyl) 12종이었고, 평가대상식품은 국내에서 유통되는 다소비식품을 위주로 곡류 4종(쌀, 보리, 밀, 옥수수), 과일류 5종(사과, 감, 밀감, 바나나, 배), 및 채소류 13종(배추, 양배추, 상추, 시금치, 오이, 토마토, 호박, 양파, 고추, 마늘, 무, 파, 당근)을 포함하여 총 22종의 식품을 대상으로 하였으며, 시료의 대표성을 부여하기 위하여 샘플링은 전국 4개 대도시(서울, 부산, 광주, 대전)를 대상으로 총2회 실시하였다. 12종의 유기인계 농약의 동시다중 노출에 대한 위해성평가를 위하여 노출평가시 TEF(독성등가치, Toxic Equivalency Factor) 방법을 적용하였고, FAO/WHO 의 만성인체노출평가방법을 기초로 우리나라 일반 성인을 대상으로 다수의 식품섭취를 통한 다수의 농약에 대한, 동시인체노출평가를 실시하였다. 노출의 안전수준을 결정하기 위해 필요한 독성값은 chlorpyrifos를 기준으로 하여 U.S.EPA 에서 제시한 AChE저해작용을 endpoint로 하는 RfD 값을 활용하였으며, 다수의 유기인계 농약으로부터 동시노출 되었을 때 나타날 수 있는 비발암독성에 대한 위해도를 결정하기 위하여 위험지수(Hazard Index, HI) 방법을 사용하였다.

• Journal of Periodontal and Implant Science
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• 제50권6호
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• pp.379-391
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• 2020

Purpose: The aims of this study were to evaluate the 5-year cumulative survival rate (CSR) of implants placed with guided bone regeneration (GBR) compared to implants placed in native bone, and to identify factors contributing to implant failure in regenerated bone. Methods: This retrospective cohort study included 240 patients who had implant placement either with a GBR procedure (regenerated bone group) or with pristine bone (native bone group). Data on demographic features (age, sex, smoking, and medical history), location of the implant, implant-specific features, and grafting procedures and materials were collected. The 5-year CSRs in both groups were estimated using Kaplan-Meier analysis. Risk factors for implant failure were analyzed with a Cox proportional hazards model. Results: In total, 264 implants in the native bone group and 133 implants in the regenerated bone group were analyzed. The 5-year CSRs were 96.4% in the regenerated bone group and 97.5% in the native bone group, which was not a significant difference. The multivariable analysis confirmed that bone status was not an independent risk factor for implant failure. However, smoking significantly increased the failure rate (hazard ratio, 10.7; P=0.002). Conclusions: The 5-year CSR of implants placed in regenerated bone using GBR was comparable to that of implants placed in native bone. Smoking significantly increased the risk of implant failure in both groups.

• Journal of Radiation Protection and Research
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• 제47권1호
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• pp.22-29
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• 2022

Background: A comprehensive, traceable, and easy-to-understand radiation risk indicator is desired for radiological protection. The early-onset hypothesis could be used for this purpose. Materials and Methods: An indicator for early death (IED) was developed and calculated using the epidemiological dataset from the 14^th Report of the Life Span Study (LSS) of Hiroshima and Nagasaki. By clarifying the calculation process, IED for all-cause mortality was estimated. In addition, the characteristics of IED for solid cancer mortality and cardiovascular mortality as well as those of men and women, and their dependence on age at exposure were investigated for detailed analysis. Results and Discussion: The IED for all-cause mortality was estimated to be approximately 4 years for an acute radiation exposure of 1 Gy regardless of the fitting dose range. The cumulative death rate for all solid cancers also indicated the early-death tendency (approximately 7-10 years at 1 Gy). Although, there is a slight difference in the characteristics of the risk obtained from the LSS study and this study, it is considered that the IED in a unit of years can also be used to show the overall picture of risk due to radiation exposure. Conclusion: We developed and calculated the indicator for early death, IED, for the cumulative mortality rate of all causes of death, all solid cancers, and circulatory diseases. The quantitative values of IED were estimated to be 4 years for all causes of death, 7-10 years for all solid cancers. IED has an advantage for intuitively understanding the meaning of radiation risk since it can be obtained by a simple and traceable method.

• Nutritional Sciences
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• 제6권3호
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• pp.173-184
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• 2003

Objective : This study was carried out to develop a semi-quantitative food frequency Questionnaire (SQFFQ) for estimating average dietary intake to determine the risk factor for lifestyle-related diseases in a conjoint cohort study. Design : We developed an SQFFQ for genomic epidemiological studies based on the data in the'98 Korea Health and Nutrition Examination Survey. A subset of data on informative food items was collected using the 24-hr recall method with 2,714 adults aged 40 or older living in middle-sized cities or in rural areas in Korea. The cumulative percent contribution and cumulative multiple regression coefficients of 17 nutrients (energy, fat, carbohydrate, protein, fiber, iron, potassium, sodium, calcium, phosphorus, vitamin A, retinol, $\beta$-carotene, vitamin $B_1$, vitamin $B_2$, niacin and vitamin C) of each food were computed. Results : Two hundred and forty-nine foods, which were selected based on their 0.9 cumulative percent contribution, and 254 foods, which were selected based on their 0.9 cumulative multiple regression coefficients, respectively, were grouped into 97 food groups according to their nutrient contents. Several popular Korean foods, which were missing from the list due to the seasonality of the survey, were included. The portion sizes were derived from the same data set. The SQFFQ covered 84.8 percent of the intake of 17 nutrients in the one day diet record data of our 326 cohort study subjects. Conclusions . The final list included 103 food items. The foods list in the SQFFQ described herein accounted for 84.8 percent of the average intake of 17 nutrients. Therefore, the list could be used for the assessment of the baseline dietary intakes of the conjoint cohort studies.

• 산업융합연구
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• 제5권1호
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• pp.45-59
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• 2007

This paper empirically examines the portfolio diversification effect using data from both KOSPI and KOSDAQ. In KOSPI market, portfolio diversification effect disappears when more than 18 stocks are added in the portfolio. About 63% of portfolio risk is eliminated. In KOSDAQ market, the maximum portfolio diversification effect is achieved when 17 stocks are at least included in a portfolio. The maximum cumulative risk reduction is 35%.

• 한국항해항만학회지
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• 제37권5호
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• pp.453-461
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• 2013

본 논문에서는 소형 해상 부유체의 위기 평가를 위한 확률기반 위기평가기법(PET)에서 표본 데이터에 최적인 누적분포함수(CDF) 추정에 관한 평가절차와 실험결과를 기술하였다. CDF는 PET에서 부유체의 위기수준을 평가하기 위한 위기허용기준의 참조 값을 제공하기 위한 것으로, 부유체 모델의 롤(Roll), 피치(pitch), 히브(Heave) 등의 운동응답함수에 대한 표본 데이터에서 추정할 수 있다. 본 연구에서는 여덟가지 정형화된 분포함수와 최대우도추정기법을 적용하여 표본 데이터에 대해서 최대우도를 갖는 CDF들을 평가하였다. 분포함수들의 적합도 검정 실험을 통해서, 베타 분포가 롤과 피치 표본 데이터에 대해서 평균 확률오차 $\bar{\delta}(0{\leq}\bar{\delta}{\leq}1.0)$가 가장 작은 0.024와 0.022로 최적임을 나타냈고, 히브 표본 데이터에 대해서는 감마 분포가 $\bar{\delta}$가 가장 작은 0.027로 최적임을 나타냈다. 본 연구에서 제안한 방법은 표본 데이터의 최적분포 추정을 위한 다양한 분야에 적용 가능할 것으로 기대된다.

• 한국독성학회:학술대회논문집
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• 한국독성학회 2003년도 추계학술대회
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• pp.34-63
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• 2003

Idiopathic Parkinson's disease (IPD) represents a common neurodegenerative disorder. While epidemiological studies have suggested a number of risk factors including age, gender, race, and inherited disorder, the cumulative evidence supports the view that environmental or occupational exposure to certain chemicals may contribute to the initiation and progress of Parkinsonism.(omitted)

• 한국화재소방학회논문지
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• 제20권1호
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• pp.6-14
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• 2006

가스로 인한 화재 및 폭발사고의 예측 가능한 프로그램을 구체화하고, 적절한 사회적 위험기준을 제시하기 위하여 최근 11년간의 가스사고 데이터베이스를 분석하였다. 먼저 동일유형의 가스사고 발생가능 성을 판단할 수 있는 Poisson 분석 방법을 적용하기 위해 3개의 사고유형, 즉 누출, 폭발, 화재로 구분하여 총 16개 항목으로 나누어서 적용하였다. 그 결과, 시공 작업 부주의-폭발-배관의 항목의 사고발생반도가 가장 작았으며, 배관연결부이완부식-누출-배관의 경우는 가장 높은 빈도를 나타내었다. 따라서 이에 대한 적절한 가스사고 대응책이 마련되어야 할 것이다. 또한 치명적인 가스사고의 추세와 합리적인 위험정책에 대한 지침을 결정하기위해 D. O. Hagon 방정식과 회기직선식을 이용하여 F.N 곡선의 누적사망자의 최소 및 최대점에 대응시켜 허용가능영역을 설정하였다. 향후 가스사고에 대한 신뢰성 있는 분석을 위해서는 가스로 인한 화재 폭발사고에 대한 데이터베이스를 지속적으로 확충보완을 시켜야 되며, 이를 위한 표준 코드화 작업이 요구된다.

• 한국산업보건학회지
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• 제8권1호
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• pp.24-35
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• 1998

Cumulative trauma disorders(CTDs) have been a growing problems for US and European industries with higher incidence rate every year. The increase and their associated costs has led companies to form committes and implement programs to address this problem. In our country, we have just started to recognize and to work on the problems in industry. This study conducted an ergonomic analysis for typical jobs of ship building industry which was not usually surveyed for CTD problem. A baseline CTD checklist which was supposed to do a risk assessment was developed and applied in this study. Initially, we considered five major parts in the checklist which consisted of personal, frequency, posture, force, and miscellaneous information. Most jobs in ship building industry were much different from typical assembly work and VDT work that have been major part of the previous CTD studies. Specifically, job characteristics in terms of frequency and posture were quite different. There were relatively long cycle time, awkward postures for whole body (not just for upper extremities). Also, CTD risk scores based on checklist were a lot higher than the scores for VDT jobs which was a case of preceding application of the checklist. Specifically, grinding jobs turned out to be the most risky one in terms of CTDs. In conclusion, usual CTD prevention guidelines are not likely to he effective in this type of industry. An individual job based interventions are strongly suggested to have a good control of CTD problems in ship building industry.