• Communications for Statistical Applications and Methods
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• v.18 no.6
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• pp.787-798
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• 2011

In this paper, we develop some characterization results in terms of survival entropy of the first order statistic. In addition, we generalize the cumulative entropy recently proposed by Di Crescenzo and Logobardi (2009) to a new measure of information (called the failure entropy) and study some properties of it and its dynamic version. Furthermore, power distribution is characterized based on dynamic failure entropy.

• Journal of Korean Society for Quality Management
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• v.18 no.1
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• pp.9-20
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• 1990

The purpose of this paper is to propose the modified semiparametric estimators for survival function in the Cox's regression model with randomly censored data based on Tsiatis and Breslow estimators, and present their asymptotic variances estimates. The proposed estimators are compared to Tsiatis, Breslow, and Kaplan-Meier estimators through a small-sample Monte Carlo study. The simulation results show that the proposed estimators are preferred for small sample sizes.

• Communications for Statistical Applications and Methods
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• v.3 no.2
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• pp.119-127
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• 1996

In this paper, we derive the Hall-Wellner band and the equal precistion band for survival function based on Hjort when the data are randomly right censored. The bands ate illustrated and compared by applying them to data from a preoperative radiation therapy.

• Journal of the Korean Statistical Society
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• v.32 no.1
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• pp.25-32
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• 2003

In this paper, we define the mean life process for the right censored data and show the asymptotic equivalence between two kinds of the mean life processes. We use the Kaplan-Meier and Susarla-Van Ryzin estimates as the estimates of survival function for the construction of the mean life processes. Also we show the asymptotic equivalence between two mean residual life processes as an application and finally discuss some difficulties caused by the censoring mechanism.

• The Korean Journal of Nuclear Medicine
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• v.35 no.4
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• pp.251-257
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• 2001

Purpose: We investigated the possibility of early postoperative Tc-99m DTPA scintigraphy in predicting long-term renal transplant survival. Materials and Methods: 64 living donor (LD) grafts were divided into two groups according to the graft function on early post-operative renal scintigraphy. Survival analysis was performed using Kaplan-Meier method and Cox proportional hazard model. Chi-square test was performed to evaluate the difference in the frequency of acute rejection. Results: Cumulative renal transplant survival was decreased in 11 patients with abnormal renal scintigraphy, but it was not statistically significant. Decreased graft function on early post-operative renal scintigraphy was not a predictor of long-term graft survival. The frequency of acute rejection was higher in abnormal scintigraphy group, and the difference was statistically significant. Conclusion: Decreased graft function on early post-operative renal scintigraphy has no direct effect on long-term renal transplant survival in LD transplantation. But it may have an indirect elect through increasing the frequency of acute rejection.

• Journal of Korean Society of Forest Science
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• v.88 no.3
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• pp.320-326
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• 1999

In this study, 15 survival functions in integral and difference forms for forest plantation were derived based on assumptions for the number of surviving trees and the differential forms of the mortality rate model. Then, performance of the models was evaluated by fitting to remeasurement data of unthinned white pine(Pinus strobes) forest plantation. As a result, three equations associated with a power function of age, $t^{\beta}$, are somewhat more suitable for describing the effect of self-thinning over time. On the other hand, a general survival function for Japanese larch(Larix leptolepts) forest plantation was derived in order to exam the effect of site quality on self-thinning procedures. The results indicate that the $N_{min}$ is negatively correlated with site index and, even though the same initial stand density was assumed, the survival function curves differ in shapes associated with site index values.

• Communications for Statistical Applications and Methods
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• v.8 no.1
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• pp.127-135
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• 2001

In this paper, we consider a simple method for testing the assumption of independent censoring on the basis of a Cox proportional hazards regression model with a time-dependent covariate. This method involves a two-stage sampling in which a random subset of censored observations is selected and followed-up until their true survival times are observed. Lee and Wolfe(1998) proposed an adjusted estimate of the survivor function for the dependent censoring under a proportional hazards alternative. This paper extends their result to obtain a bootstrap confidence interval for the adjusted survivor function under the dependent censoring. The proposed procedure is illustrated with an example of a clinical trial for lung cancer analysed in Lee and Wolfe(1998).

• Korean Journal of Microbiology
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• v.23 no.1
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• pp.49-55
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• 1985

The survival of Escherichia coli in river water was comparatively studied by laboratory and in sity study methods. The survival by two methods was evaluated as a function of E. coli strain, indigeneous predator, level of water pollution, and water temperature in different season. The survival rate of E. coli examined by laboratory method was lower than that by in situ method. That was found to be due to the fact that higher number of predator was maintained in labortory study than in in situ study. The survival rates of E. coli in gradually polluted river waters could be differentiated by in situ study, but not by laboratory study. Therefore, an in situ method rather than labortory method was thought to be a choice of study method for the survival of E. coli in river waters.

• Journal of Korean Neurosurgical Society
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• v.50 no.3
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• pp.216-223
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• 2011

Objective : The purposes of this study are to estimate postoperative survival and ambulatory outcome and to identify prognostic factors thereafter of metastatic spinal tumors in a single institute. Methods : We reviewed the medical records of 182 patients who underwent surgery for a metastatic spinal tumor from January 1987 to January 2009 retrospectively. Twelve potential prognostic factors (age, gender, primary tumor, extent and location of spinal metastases, interval between primary tumor diagnosis and metastatic spinal cord compression, preoperative treatment, surgical approach and extent, preoperative Eastern Cooperative Oncology Group (ECOG) performance status, Nurick score, Tokuhashi and Tomita score) were investigated. Results : The median survival of the entire patients was 8 months. Of the 182 patients, 80 (44%) died within 6 months after surgery, 113 (62%) died within 1 year after surgery, 138 (76%) died within 2 years after surgery. Postoperatively 47 (26%) patients had improvement in ambulatory function, 126 (69%) had no change, and 9 (5%) had deterioration. On multivariate analysis, better ambulatory outcome was associated with being ambulatory before surgery (p=0.026) and lower preoperative ECOG score (p=0.016). Survival rate was affected by preoperative ECOG performance status (p<0.001) and Tomita score (p<0.001). Conclusion : Survival after metastatic spinal tumor surgery was dependent on preoperative ECOG performance status and Tomita score. The ambulatory functional outcomes after surgery were dependent on preoperative ambulatory status and preoperative ECOG performance status. Thus, prompt decompressive surgery may be warranted to improve patient's survival and gait, before general condition and ambulatory function of patient become worse.

• Journal of the Korean Data and Information Science Society
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• v.4
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• pp.1-11
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• 1993

The Cox's regression model is frequently used for covariate effects in survival data analysis, But, much of the statistical work has focused on asymptotic behavior so the small sample evaluation has been neglected. In this paper, we compare the small or moderate sample performances of the survival function estimators for the Cox's regression model using bootstrap method. The smoothed PL type estimator and the Link estimator are slightly better than corresponding the PL type estimator and the Nelson type estimator in the sense of the achieved error rates.