In this article, we use penalized spline to estimate the hazard function from a set of censored failure time data. A new approach to estimate the amount of smoothing is provided. Under regularity conditions we establi...In this article, we use penalized spline to estimate the hazard function from a set of censored failure time data. A new approach to estimate the amount of smoothing is provided. Under regularity conditions we establish the consistency and the asymptotic normality of the penalized likelihood estimators. Numerical studies and an example are conducted to evaluate the performances of the new procedure.展开更多
In this article, the lifetime data subjecting to right random censoring is considered. Nonparametric estimation of the distribution function based on the conception of presmoothed estimation of relative-risk function ...In this article, the lifetime data subjecting to right random censoring is considered. Nonparametric estimation of the distribution function based on the conception of presmoothed estimation of relative-risk function and the properties of the estimator by using methods of numerical modeling are discussed. In the model under consideration, the estimates were compared using numerical methods to determine which of the estimates is actually better.展开更多
This work studies a proportional hazards model for survival data with ＂long-term survivors＂, in which covariates are subject to linear measurement error. It is well known that the naive estimators from both partial ...This work studies a proportional hazards model for survival data with ＂long-term survivors＂, in which covariates are subject to linear measurement error. It is well known that the naive estimators from both partial and full likelihood methods are inconsistent under this measurement error model. For measurement error models, methods of unbiased estimating function and corrected likelihood have been proposed in the literature. In this paper, we apply the corrected partial and full likelihood approaches to estimate the model and obtain statistical inference from survival data with long-term survivors. The asymptotic properties of the estimators are established. Simulation results illustrate that the proposed approaches provide useful tools for the models considered.展开更多
电力设备经济寿命的定量预测能为设备运维决策和电网规划提供依据。构建了以年等值成本最低为依据的变压器经济寿命预测模型。为计算模型中的关键参数,将变压器的全寿命数据进行分类和关键数据提取,采用无分布的比例故障率模型和蒙特卡...电力设备经济寿命的定量预测能为设备运维决策和电网规划提供依据。构建了以年等值成本最低为依据的变压器经济寿命预测模型。为计算模型中的关键参数,将变压器的全寿命数据进行分类和关键数据提取,采用无分布的比例故障率模型和蒙特卡洛模拟法计算得到故障率和停机持续时间的概率分布。然后分析经济要素,在计算电力变压器的年度检修成本、年度中断成本和年度运行成本的基础上,实现了电力变压器经济寿命的定量预测。最后以一台实际的220 k V现役变压器为例,按照所建立的预测模型进行了经济寿命预测的实证研究,结果表明预测模型不仅能有效利用设备寿命数据,而且预测结果合理,对变压器的运维决策,以及未来变电站的规划改造具有指导意义。展开更多
Background Cyclo-oxgenase 2 (COX-2) is involved in prostaglandin synthesis in central nervous system, and it also plays a role in human carcinogenesis Our purpose of this study is to investigate the COX-2 expressi...Background Cyclo-oxgenase 2 (COX-2) is involved in prostaglandin synthesis in central nervous system, and it also plays a role in human carcinogenesis Our purpose of this study is to investigate the COX-2 expression in different development stages of colorectal cancer, and to discuss the relationship between the gene expression and clinicopathological features of the cancer Methods COX-2 expression was examined by immunohistochemical staining in 76 surgical specimens of colorectal cancer (44 of advanced stage and 32 of early stage), thirty-three adenomas and 18 normal colonic mucosal tissues taken by endoscopic biopsy Kaplan-Meier survival curves and Cox proportional hazards regression were used to evaluate the relation of COX-2 to prognosis Results COX-2 expression, divided into 4 grades from “-” to“+++”, is respectively 83 3%, 16 7%, 0% and 0% in normal colonic mucosal tissues; 12 1%, 42 4%, 36 4% and 9 1% in adenomas; 6 3%, 28 1%, 46 9% and 18 7% in early colorectal cancers (ECCs), and 6 8%, 20 5%, 18 2% and 54 5% in advanced colorectal cancers (CRCs) The differences in COX-2 expression between advanced CRCs and early colorectal cancers (ECCs) as well as between the advanced CRCs and adenomas were statistically significant ( P <0 01); but there was no significant difference between ECCs and adenomas Kaplan-Meier survival analysis showed a significant difference in the survival curves between low high COX-2 groups ( P <0 05) Cox proportional hazards regression showed that COX-2 expression was related to poorer long-term outcome with a hazard ratio of 2 665 unadjusted for other variables ( P <0 05), and COX-2 expression was an independent risk factor of poor prognosis KH*2/5DConclusions COX-2 expression is gradually up-regulated in the development from normal epithelium to adenomas and from ECCs to advanced CRCs Alhough the COX-2 protein can not be regarded as a tumor marker to diagnose CRCs early, COX-2 expression can be regarded as an independent risk factor展开更多
基金supported by the Natural Science Foundation of China(10771017,10971015,10231030)Key Project to Ministry of Education of the People’s Republic of China(309007)
文摘In this article, we use penalized spline to estimate the hazard function from a set of censored failure time data. A new approach to estimate the amount of smoothing is provided. Under regularity conditions we establish the consistency and the asymptotic normality of the penalized likelihood estimators. Numerical studies and an example are conducted to evaluate the performances of the new procedure.
文摘In this article, the lifetime data subjecting to right random censoring is considered. Nonparametric estimation of the distribution function based on the conception of presmoothed estimation of relative-risk function and the properties of the estimator by using methods of numerical modeling are discussed. In the model under consideration, the estimates were compared using numerical methods to determine which of the estimates is actually better.
基金supported by the National Nature Science Foundation of China under Grant No.10871084Macquarie University Safety Net grant
文摘This work studies a proportional hazards model for survival data with ＂long-term survivors＂, in which covariates are subject to linear measurement error. It is well known that the naive estimators from both partial and full likelihood methods are inconsistent under this measurement error model. For measurement error models, methods of unbiased estimating function and corrected likelihood have been proposed in the literature. In this paper, we apply the corrected partial and full likelihood approaches to estimate the model and obtain statistical inference from survival data with long-term survivors. The asymptotic properties of the estimators are established. Simulation results illustrate that the proposed approaches provide useful tools for the models considered.
文摘电力设备经济寿命的定量预测能为设备运维决策和电网规划提供依据。构建了以年等值成本最低为依据的变压器经济寿命预测模型。为计算模型中的关键参数,将变压器的全寿命数据进行分类和关键数据提取,采用无分布的比例故障率模型和蒙特卡洛模拟法计算得到故障率和停机持续时间的概率分布。然后分析经济要素,在计算电力变压器的年度检修成本、年度中断成本和年度运行成本的基础上,实现了电力变压器经济寿命的定量预测。最后以一台实际的220 k V现役变压器为例,按照所建立的预测模型进行了经济寿命预测的实证研究,结果表明预测模型不仅能有效利用设备寿命数据,而且预测结果合理,对变压器的运维决策,以及未来变电站的规划改造具有指导意义。
基金ThisinvestigationwaspartlysupportedbytheGuangdongprovinceNatureScienceFund (No 0 13 14 7)
文摘Background Cyclo-oxgenase 2 (COX-2) is involved in prostaglandin synthesis in central nervous system, and it also plays a role in human carcinogenesis Our purpose of this study is to investigate the COX-2 expression in different development stages of colorectal cancer, and to discuss the relationship between the gene expression and clinicopathological features of the cancer Methods COX-2 expression was examined by immunohistochemical staining in 76 surgical specimens of colorectal cancer (44 of advanced stage and 32 of early stage), thirty-three adenomas and 18 normal colonic mucosal tissues taken by endoscopic biopsy Kaplan-Meier survival curves and Cox proportional hazards regression were used to evaluate the relation of COX-2 to prognosis Results COX-2 expression, divided into 4 grades from “-” to“+++”, is respectively 83 3%, 16 7%, 0% and 0% in normal colonic mucosal tissues; 12 1%, 42 4%, 36 4% and 9 1% in adenomas; 6 3%, 28 1%, 46 9% and 18 7% in early colorectal cancers (ECCs), and 6 8%, 20 5%, 18 2% and 54 5% in advanced colorectal cancers (CRCs) The differences in COX-2 expression between advanced CRCs and early colorectal cancers (ECCs) as well as between the advanced CRCs and adenomas were statistically significant ( P <0 01); but there was no significant difference between ECCs and adenomas Kaplan-Meier survival analysis showed a significant difference in the survival curves between low high COX-2 groups ( P <0 05) Cox proportional hazards regression showed that COX-2 expression was related to poorer long-term outcome with a hazard ratio of 2 665 unadjusted for other variables ( P <0 05), and COX-2 expression was an independent risk factor of poor prognosis KH*2/5DConclusions COX-2 expression is gradually up-regulated in the development from normal epithelium to adenomas and from ECCs to advanced CRCs Alhough the COX-2 protein can not be regarded as a tumor marker to diagnose CRCs early, COX-2 expression can be regarded as an independent risk factor
