• 한국신뢰성학회지:신뢰성응용연구
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• 제16권1호
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• pp.56-63
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• 2016

Purpose: The purpose of this study is to point out that the Kaplan-Meier method is not valid to calculate the survival probability or failure probability (risk) in the presence of competing risks and to introduce more valid method of cumulative incidence function. Methods: Survival analysis methods have been widely used in biostatistics division. However the same methods have not been utilized in reliability division. Especially competing risks cases, where several causes of failure occur and the occurrence of one event precludes the occurrence of the other events, are scattered in reliability field. But they are not noticed in the realm of reliability expertism or they are analysed in the wrong way. Specifically Kaplan-Meier method which assumes that the censoring times and failure times are independent is used to calculate the probability of failure in the presence of competing risks, thereby overestimating the real probability of failure. Hence, cumulative incidence function is introduced and sample competing risks data are analysed using cumulative incidence function and some graphs. Finally comparison of cumulative incidence functions and regression type analysis are mentioned briefly. Results: Cumulative incidence function is used to calculate the survival probability or failure probability (risk) in the presence of competing risks and some useful graphs depicting the failure trend over the lifetime are introduced. Conclusion: This paper shows that Kaplan-Meier method is not appropriate for the evaluation of survival or failure over the course of lifetime. In stead, cumulative incidence function is shown to be useful. Some graphs using the cumulative incidence functions are also shown to be informative.

• 한국신뢰성학회지:신뢰성응용연구
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• 제18권2호
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• pp.130-142
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• 2018

Purpose: The purpose of this study is to introduce regression method in the presence of competing risks and to show how you can use the method with hypothetical data. Methods: Survival analysis has been widely used in biostatistics division. But the same method has not been utilized in reliability division. Especially competing risks, where more than a couple of causes of failure occur and the occurrence of one event precludes the occurrence of the other events, are scattered in reliability field. But they are not utilized in the area of reliability or they are analysed in the wrong way. Specifically Kaplan-Meier method is used to calculate the probability of failure in the presence of competing risks, thereby overestimating the real probability of failure. Hence, cumulative incidence function is introduced. In addition, sample competing risks data are analysed using cumulative incidence function along with some graphs. Lastly we compare cumulative incidence functions with regression type analysis briefly. Results: We used cumulative incidence function to calculate the survival probability or failure probability in the presence of competing risks. We also drew some useful graphs depicting the failure trend over the lifetime. Conclusion: This research shows that Kaplan-Meier method is not appropriate for the evaluation of survival or failure over the course of lifetime in the presence of competing risks. Cumulative incidence function is shown to be useful in stead. Some graphs using the cumulative incidence functions are also shown to be informative.

• Communications for Statistical Applications and Methods
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• 제23권6호
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• pp.555-562
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• 2016

Interval censored data often occur in an observational study where the subject is followed periodically. Instead of observing an exact failure time, two inspection times that include it are available. There are several methods to analyze interval censored failure time data (Sun, 2006). However, in the presence of competing risks, few methods have been suggested to estimate covariate effect on interval censored competing risk data. A sub-distribution hazard model is a commonly used regression model because it has one-to-one correspondence with a cumulative incidence function. Alternatively, Klein and Andersen (2005) proposed a pseudo-value approach that directly uses the cumulative incidence function. In this paper, we consider an extension of the pseudo-value approach into the interval censored data to estimate regression coefficients. The pseudo-values generated from the estimated cumulative incidence function then become response variables in a generalized estimating equation. Simulation studies show that the suggested method performs well in several situations and an HIV-AIDS cohort study is analyzed as a real data example.

• 응용통계연구
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• 제31권4호
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• pp.529-538
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• 2018

결핵은 높은 이환과 사망을 일으키는 질병으로 현대의학의 발달에 따라 발생률과 사망률은 감소하고 있다. 그러나 한국은 아직까지 OECD 국가 중 결핵 발생률과 사망률이 가장 높다. 이에 따라 한국은 결핵의 예방 및 통제를 위해 여러 정책 사업을 실시하고 있다. 본 연구에서는 공공민간협력(public-private mix) 결핵관리사업이 치료결과에 미치는 영향을 분석하고 결핵환자의 치료 성공에 영향을 미치는 요인을 확인하고자 한다. 질병관리본부에서 관리하는 결핵환자 신고 자료를 이용하여 2012-2015년 전국 결핵 신환자 코호트 약 13만명을 대상으로 분석하였다. 누적 발생 함수(cumulative incidence function)를 이용하여 요인별로 누적 치료 성공률을 비교하였으며. 주 관심사건(치료성공) 및 경쟁사건(사망)을 고려한 두 가지 경쟁위험모형(cause-specific Cox's proportional hazards model and subdistribution hazard model)을 사용하여 분석 결과를 비교하였다.

• 응용통계연구
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• 제20권2호
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• pp.357-371
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• 2007

경쟁위험(competing risk) 하에서의 누적 발생함수(cumulative incidence function)는 일반적으로 비모수적 방법으로 추정된다. 그러나 관심 있는 원인에 의한 사건이 다른 원인에 의한 사건보다 상대적으로 적게 발생하는 경우에 비모수적 방법으로 추정된 누적발생함수는 이산성으로 인해 다소 정확하지 않게 된다. 이와 같은 경우에 Bryant와 Diagnam(2004)는 관심 있는 원인에 대한 원인특정적 위험함수(cause-specific hazard function)를 모수적으로 모형화하고 다른 원인에 의한 사건은 비모수적으로 추정하는 준모수적 방법을 제안했다. 본 연구에서는 준모수적 누적발생함수 추정량을 재표현하고 와이블분포모형과 대수 정규분포모형으로 확장하였다. 또한 대수 정규분포 원인특정적 위험모형일 경우 누적 발생함수에 대한 비모수적 추정량, 와이블분포 준모수적 추정량과 대수 정규분포 준모수적 추정량의 효율성을 비교하며 준모수적 추정량의 성능과 모형 오설정이 미치는 영향을 살펴보았다.

• Communications for Statistical Applications and Methods
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• 제30권1호
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• pp.1-19
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• 2023

Observational data with missing or incomplete data are common in biomedical research. Multiple imputation is an effective approach to handle missing data with the ability to decrease bias while increasing statistical power and efficiency. In recent years propensity score (PS) matching has been increasingly used in observational studies to estimate treatment effect as it can reduce confounding due to measured baseline covariates. In this paper, we describe in detail approaches to competing risk analysis in the setting of incomplete observational data when using PS matching. First, we used multiple imputation to impute several missing variables simultaneously, then conducted propensity-score matching to match statin-exposed patients with those unexposed. Afterwards, we assessed the effect of statin exposure on the risk of heart failure-related hospitalizations or emergency visits by estimating both relative and absolute effects. Collectively, we provided a general methodological framework to assess treatment effect in incomplete observational data. In addition, we presented a practical approach to produce overall cumulative incidence function (CIF) based on estimates from multiple imputed and PS-matched samples.

• Journal of the Korean Data and Information Science Society
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• 제26권6호
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• pp.1271-1281
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• 2015

본 논문에서는 '제1회 산재보험패널조사'에서 제공된 자료를 이용하여 산재 근로자의 경제 활동 유형의 특성을 연구하였다. 조사 대상자는 2012년도에 산재 요양을 종결한 근로자이며 총 2,000명이 지역, 장해등급 및 재활서비스 이용여부로 층화계통추출되었다. 본 연구에서는 근로자가 산재 후 참여하는 경제활동의 유형으로 원직장복귀뿐만 아니라 다른 직장으로의 재취업의 가능성을 고려하여 이러한 경제활동으로의 이동에 어떤 요인이 영향을 미치는지 조사하고자 한다. 원직장복귀에 영향을 미치는 요인을 분석하기 위하여 총 1,463명의 연구 대상자에게 경쟁위험 분석방법을 적용하였다. 또한 경제활동상태에 영향을 미치는 요인을 세 가지 유형 (산재 근로자의 특성, 재해 사업장의 특성, 산업재해의 특성)으로 나누어 통합 분석을 시행하였다. 분석 결과를 통해 학력이 높고 근로기간이 길수록 원직장복귀가 빨라짐을 알 수 있었다. 또한 연령이 높고, 기능원 및 관련 기능직에 종사자이며, 장해의 정도가 심한 산재 근로자가 원직장복귀까지 더 오랜 시간이 걸렸음을 알 수 있었다.

• Safety and Health at Work
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• 제12권2호
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• pp.174-183
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• 2021

Background: Toluene diisocyanate (TDI) is a highly reactive chemical that causes sensitization and has also been associated with increased lung cancer. A risk assessment was conducted based on occupational epidemiologic estimates for several health outcomes. Methods: Exposure and outcome details were extracted from published studies and a NIOSH Health Hazard Evaluation for new onset asthma, pulmonary function measurements, symptom prevalence, and mortality from lung cancer and respiratory disease. Summary exposure-response estimates were calculated taking into account relative precision and possible survivor selection effects. Attributable incidence of sensitization was estimated as were annual proportional losses of pulmonary function. Excess lifetime risks and benchmark doses were calculated. Results: Respiratory outcomes exhibited strong survivor bias. Asthma/sensitization exposure response decreased with increasing facility-average TDI air concentration as did TDI-associated pulmonary impairment. In a mortality cohort where mean employment duration was less than 1 year, survivor bias pre-empted estimation of lung cancer and respiratory disease exposure response. Conclusion: Controlling for survivor bias and assuming a linear dose-response with facility-average TDI concentrations, excess lifetime risks exceeding one per thousand occurred at about 2 ppt TDI for sensitization and respiratory impairment. Under alternate assumptions regarding stationary and cumulative effects, one per thousand excess risks were estimated at TDI concentrations of 10 - 30 ppt. The unexplained reported excess mortality from lung cancer and other lung diseases, if attributable to TDI or associated emissions, could represent a lifetime risk comparable to that of sensitization.

• The Korean Journal of Pain
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• 제13권1호
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• pp.31-37
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• 2000

Background: Recent studies suggested that a preoperative block of N-methyl-D-aspartate (NMDA) receptors with NMDA antagonists may reduce postoperative pain. In this double-blind study, magnesium sulfate, a natural NMDA receptor antagonist, was administered preoperatively to investigate the effects of magnesium sulfate on postoperative pain and pulmonary function. Methods: Seventy patients who were to undergo gastrectomy under general anesthesia were randomly assigned to one of three groups. Groups 2 and 3 received intravenous magnesium, preoperatively (Group 2: 50 mg/kg bolus, 7.5 mg/kg/hr for 20 hr, Group 3: 50 mg/kg bolus, 15 mg/kg/hr for 20 hr). Group 1 received normal saline as the control group. Visual analog scale (VAS) for postoperative pain and mood, cumulative analgesic consumption, recovery of pulmonary function and side effects were evaluated at 6, 24, 48 and 72 hours after the operation. Results: In Groups 2 and 3, plasma concentration of magnesium were significantly higher than in Group 1 at 6 and 20 hours after infusion (P<0.05). There were no significant differences in the analgesic consumption, and recovery of pulmonary function and the incidence of side effects at 6, 24, 48 and 72 hours after the operation among the three groups. In Group 3, pain scores at rest measured 24 and 48 hours after operation were lower than the control group, and pain scores when deep breathing were significantly lower than the control group at postoperative 6, 24, 48, and 72 hours. Conclusions: We conclude that intravenous infusion of greater amount of magnesium has little effectiveness in reducing postoperative pain. However, further studies are needed to characterize the clinical significance of these effects on postoperative pain.

• 구강회복응용과학지
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• 제27권4호
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• pp.449-454
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• 2011

근래에 비스포스포테이트(bisphosphonate) 투약의 부작용으로 악골괴사에 관한 보고들이 점차적으로 증가하고 있다. 최근에 보고된 유병율은 대략 0.8% - 12 % 정도이다. 하악은 상악보다 2배 정도 호발하는 것으로 보고되었고 이의 60 - 70 %는 치과진료와 연관성이 거론되었다. 임상적으로 골괴사 현상이 일어나기 전에 건강한 치주조직에 변화가 일어나는데 치유지연 점막궤양, 치아동요와 원인을 알 수 없는 연조직 감염등이 관찰되었다. 치아발거가 치과영역에서 가장 흔한 사전 처치행위로 알려져 있다. 장기적인 비스포스포네이트 투약시 세심한 예방적 치과진료가 이러한 심각한 괴사로 이어지지 않도록 하는데 절대적이다.