We propose the single-index hazards model for censored survival data.As an extension of the Cox model and many transformation models,this model allows nonparametric modeling of covariate effects in a parsimonious way ...We propose the single-index hazards model for censored survival data.As an extension of the Cox model and many transformation models,this model allows nonparametric modeling of covariate effects in a parsimonious way via a single index.In addition,the relative importance of covariates can be assessed via this model.We consider two commonly used profile likelihood methods for parameter estimation:the local profile likelihood method and the stratified profile likelihood method.It is shown that both methods may give consistent estimators under certain restrictive conditions,but in general they can yield biased estimation.Simulation studies are also conducted to demonstrate these bias phenomena.The existence and nature of the failures of these two commonly used approaches is somewhat surprising.展开更多
Through the implementation of national bowel cancer screening programmes we have seen a three-fold increase in early pT1 colorectal cancers, but how these lesions should be managed is currently unclear. Local excision...Through the implementation of national bowel cancer screening programmes we have seen a three-fold increase in early pT1 colorectal cancers, but how these lesions should be managed is currently unclear. Local excision can be an attractive option, especially for fragile patients with multiple comorbidities, but it is only safe from an oncological point of view in the absence of lymph node metastasis. Patient risk stratification through careful analysis of histopathological features in local excision or polypectomy specimens should be performed according to national guidelines to avoid under-or over-treatment. Currently national guidelines vary in their recommendations as to which factors should be routinely reported and there is no established multivariate risk stratification model to determine which patients should be offered major resectional surgery.Conventional histopathological parameters such as tumour grading or lymphovascular invasion have been shown to be predictive of lymph node metastasis in a number of studies but the inter-and intra-observer variation in reporting is high. Newer parameters including tumour budding and poorly differentiated clusters have been shown to have great potential, but again some improvement in the inter-observer variation is required. With the implementation of digital pathology into clinical practice, quantitative parameters like depth/area of submucosal invasion and proportion of stroma can be routinely assessed. In this review we present the various histopathological risk factors for predicting systemic spread in pT1 colorectal cancer and introduce potential novel quantitative variables and multivariable risk models that could be used to better define the optimal treatment of this increasingly common disease.展开更多
With the straification theory we have proved the transversal layer s 0 3,k (D) of complete equations for mixed fluid is not an empty set: s 0 3,k (D) ≠ for all k(k≥1) . Based on this conclusion a...With the straification theory we have proved the transversal layer s 0 3,k (D) of complete equations for mixed fluid is not an empty set: s 0 3,k (D) ≠ for all k(k≥1) . Based on this conclusion and the “secondary equation” of s 0 3,k (D), this paper fully presents the expressions of coefficients in all local analytic solutions of the equations. Therefore we provide the calculation formulas by which we can get the numerical solutions to any desired accuracy.展开更多
Much has been written of the error in computing the baroclinic pressure gradient (BPG) with sigma coordinates in ocean or atmospheric numerical models. The usual way to reduce the error is to subtract area-averaged de...Much has been written of the error in computing the baroclinic pressure gradient (BPG) with sigma coordinates in ocean or atmospheric numerical models. The usual way to reduce the error is to subtract area-averaged density stratification of the whole computation region. But if there is great difference between the area-averaged and the local averaged density stratification, the error will be obvious. An example is given to show that the error from this method may be larger than that from no correction sometimes. The definition of local area is put forward. Then, four improved BPG difference schemes of subtracting the local averaged density stratification are designed to reduce the error. Two of them are for diagnostic calculation (density field is fixed), and the others are for prognostic calculation (density field is not fixed). The results show that the errors from these schemes all significantly decrease.展开更多
文摘We propose the single-index hazards model for censored survival data.As an extension of the Cox model and many transformation models,this model allows nonparametric modeling of covariate effects in a parsimonious way via a single index.In addition,the relative importance of covariates can be assessed via this model.We consider two commonly used profile likelihood methods for parameter estimation:the local profile likelihood method and the stratified profile likelihood method.It is shown that both methods may give consistent estimators under certain restrictive conditions,but in general they can yield biased estimation.Simulation studies are also conducted to demonstrate these bias phenomena.The existence and nature of the failures of these two commonly used approaches is somewhat surprising.
基金Supported by Yorkshire Cancer Researchthe National Institute for Health Research+1 种基金the Pelican Cancer Foundationthe Pathological Society of Great Britain and Ireland
文摘Through the implementation of national bowel cancer screening programmes we have seen a three-fold increase in early pT1 colorectal cancers, but how these lesions should be managed is currently unclear. Local excision can be an attractive option, especially for fragile patients with multiple comorbidities, but it is only safe from an oncological point of view in the absence of lymph node metastasis. Patient risk stratification through careful analysis of histopathological features in local excision or polypectomy specimens should be performed according to national guidelines to avoid under-or over-treatment. Currently national guidelines vary in their recommendations as to which factors should be routinely reported and there is no established multivariate risk stratification model to determine which patients should be offered major resectional surgery.Conventional histopathological parameters such as tumour grading or lymphovascular invasion have been shown to be predictive of lymph node metastasis in a number of studies but the inter-and intra-observer variation in reporting is high. Newer parameters including tumour budding and poorly differentiated clusters have been shown to have great potential, but again some improvement in the inter-observer variation is required. With the implementation of digital pathology into clinical practice, quantitative parameters like depth/area of submucosal invasion and proportion of stroma can be routinely assessed. In this review we present the various histopathological risk factors for predicting systemic spread in pT1 colorectal cancer and introduce potential novel quantitative variables and multivariable risk models that could be used to better define the optimal treatment of this increasingly common disease.
文摘With the straification theory we have proved the transversal layer s 0 3,k (D) of complete equations for mixed fluid is not an empty set: s 0 3,k (D) ≠ for all k(k≥1) . Based on this conclusion and the “secondary equation” of s 0 3,k (D), this paper fully presents the expressions of coefficients in all local analytic solutions of the equations. Therefore we provide the calculation formulas by which we can get the numerical solutions to any desired accuracy.
基金The Major State Basic Research Program of China under contract No. 2002412403the National Natural Science Foundation of China un-der contract No. 40306014.
文摘Much has been written of the error in computing the baroclinic pressure gradient (BPG) with sigma coordinates in ocean or atmospheric numerical models. The usual way to reduce the error is to subtract area-averaged density stratification of the whole computation region. But if there is great difference between the area-averaged and the local averaged density stratification, the error will be obvious. An example is given to show that the error from this method may be larger than that from no correction sometimes. The definition of local area is put forward. Then, four improved BPG difference schemes of subtracting the local averaged density stratification are designed to reduce the error. Two of them are for diagnostic calculation (density field is fixed), and the others are for prognostic calculation (density field is not fixed). The results show that the errors from these schemes all significantly decrease.
