A Flexible Parametric Model for Combining Current Status and Age at First Diagnosis Data

In some cross-sectional studies of chronic disease, data consist of the age at examination, whether the disease was present at the exam, and recall of the age at first diagnosis. This article describes a flexible parametric approach for combining current status and age at first diagnosis data. We assume that the log odds of onset by a given age and of detection by a given age conditional on onset by that age are nondecreasing functions of time plus linear combinations of covariates. Piecewise linear models are used to characterize changes across time in the baseline odds. Methods are described for accommodating informatively missing current status data and inferences based on the age-specific incidence of disease prior to a landmark event (e.g., puberty, menopause). Our formulation enables straightforward maximum likelihood estimation without requiring restrictive parametric or Markov assumptions. The methods are applied to data from a study of uterine fibroids.     

The S-Distribution A Tool for Approximation and Classification of Univariate,Unimodal Probability Distributions

In many statistical applications a data set needs to be evaluated but there is no solid information about which probability distribution might be most appropriate. Typical solutions to this problems are: to make assumptions that facilitate mathematical treatment; to use a family of distribution functions that contains all relevant distributions as special cases; or, to employ nonparametric methods. All three solutions have disadvantages since assumptions are usually difficult to justify, families of distributions contain too many parameters to be of practical use, and nonparametric methods make it difficult to characterize data in a succinct quantitative form. The S-distribution introduced here is a compromise between the conflicting goals of simplicity in analysis and generality in scope. It is characterized by four parameters, one of which reflects its location, the second one its spread, and the remaining two its shape; transformation to a standard form reduces the number of free parameters to two. Cumulatives and densities are computed numerically in fractions of seconds, key features like quantiles and moments are easily obtained, and results can be presented in terms of parameter values. The S-distribution rather accurately models different distribution functions, including central and noncentral distributions, and thus competes in flexibility with some distribution families. As an approximation, the S-distribution provides a graphical method for demonstrating relationships between distributions, such as the relationships between central F, χ² and χ^?2 or central and noncentral t, χ^-1, and normal.     

The Accelerated Failure Time Model Under Biased Sampling

Summary Chen (2009, Biometrics) studies the semi‐parametric accelerated failure time model for data that are size biased. Chen considers only the uncensored case and uses hazard‐based estimation methods originally developed for censored observations. However, for uncensored data, a simple linear regression on the log scale is more natural and provides better estimators.     

Flexible hazard regression modeling for medical cost data

The modeling of lifetime (i.e. cumulative) medical cost data in the presence of censored follow-up is complicated by induced informative censoring, rendering standard survival analysis tools invalid. With few exceptions, recently proposed nonparametric estimators for such data do not extend easily to handle covariate information. We propose to model the hazard function for lifetime cost endpoints using an adaptation of the HARE methodology (Kooperberg, Stone, and Truong, Journal of the American Statistical Association, 1995, 90, 78-94). Linear splines and their tensor products are used to adaptively build a model that incorporates covariates and covariate-by-cost interactions without restrictive parametric assumptions. The informative censoring problem is handled using inverse probability of censoring weighted estimating equations. The proposed method is illustrated using simulation and also with data on the cost of dialysis for patients with end-stage renal disease.     

Simple Nonparametric Inference for Monotonic Processes

A scoring system for possibly censored monotonic processes is presented which allows to analyze such processes by means of standard parametric or nonparametric tests. In either case the analyses are invariant to monotonic transformations of time. Such analyses are of relevance whenever changes in degree of function are observed rather than the single and 100% loss of function of survival analysis. An example of gradually increasing function after particular reconstructive surgery is supplied.     

A Simple,Realistic Stochastic Model of Gastric Emptying

Several models of Gastric Emptying (GE) have been employed in the past to represent the rate of delivery of stomach contents to the duodenum and jejunum. These models have all used a deterministic form (algebraic equations or ordinary differential equations), considering GE as a continuous, smooth process in time. However, GE is known to occur as a sequence of spurts, irregular both in size and in timing. Hence, we formulate a simple stochastic process model, able to represent the irregular decrements of gastric contents after a meal. The model is calibrated on existing literature data and provides consistent predictions of the observed variability in the emptying trajectories. This approach may be useful in metabolic modeling, since it describes well and explains the apparently heterogeneous GE experimental results in situations where common gastric mechanics across subjects would be expected.     

Relating Cox's Proportional Hazard Model to the Exponential Model for Survival

An approximate representation is given for the partial likelihood estimate of the regression coefficient in Cox's proportional hazard model which indicates how it measures the association between survival time and covariate. The case of a single covariate is concentrated on. The representation is closely related to the first step of a Newton-Raphson iteration, i.e. to the score test. A similar representation for the Feigl-Zelen exponential model shows that a similar type of association is being measured, if observed lifetimes are interpreted as expected lifetimes of ordered exponentials. Necessary and sufficient conditions for the existence of Cox's estimate in the simple case are also written down.     

A Simple Model of Ostracism Formation

We study formation of ostracism in a society from a game theoretical perspective. The dynamics of group formation is complicated in that the choices of the individuals and the form of the groups mutually affect each other in the process. A suggested simple model shows that individual efforts to increase his/her own sense of belonging is responsible for both growth of groups and creation of an outcast. Once a person happens to get behind in synchronizing with others, tendency to alienate him may grow among others, possibly making him left out in the end. Alienating minority occurs even when there is a penalty for disliking and people are encouraged to favor others. Considering that the target is accidentally picked, we can understand ostracism as an inherent part of the group formation, rather than a result of specific discrepancy among people. Another finding is that a single individual who seeks for unconditional unification of the society (“philanthropist”) likely invites his/her own isolation from the society, while the existence of such person generally promotes coalition of others.     

Efficient approximate k‐fold and leave‐one‐out cross‐validation for ridge regression

In model building and model evaluation, cross‐validation is a frequently used resampling method. Unfortunately, this method can be quite time consuming. In this article, we discuss an approximation method that is much faster and can be used in generalized linear models and Cox’ proportional hazards model with a ridge penalty term. Our approximation method is based on a Taylor expansion around the estimate of the full model. In this way, all cross‐validated estimates are approximated without refitting the model. The tuning parameter can now be chosen based on these approximations and can be optimized in less time. The method is most accurate when approximating leave‐one‐out cross‐validation results for large data sets which is originally the most computationally demanding situation. In order to demonstrate the method's performance, it will be applied to several microarray data sets. An R package penalized, which implements the method, is available on CRAN.     

进展期胃癌的病理学、形态计量和免疫组织化学研究:一种新的胃癌病理-生物学分型

目的 为反映肿瘤组织的生长活性和宿主的免疫防御反应,提出一种新的胃癌病理-生物学分型,方法 用组织病理学,组织化学,免疫组织化学和形态计量方法对具有5-8年随访资料的147例进展期胃癌作了研究,并用多元逐步回归方程,对与预后有关的变量（包括存活时间,淋巴结转移,肿瘤侵袭深度,分化程度,免疫活性细胞反应,嗜酸粒细胞反应,肥大细胞反应,瘤细胞核大小,CEA标记,核分裂指数,瘤细胞密度指数,肿瘤大小,年龄和性别）做了回归分析。结果 根据肿瘤间质的反应方式和肿瘤组织生长活性,可把胃癌分为两型,即限制型和促进型;每型又以核的大小分作大核亚型和小核亚型,多个临床病理参数（存活时间,淋巴结转移,侵袭深度,免疫活性细胞反应,嗜酸粒细胞反应,肥大细胞反应,瘤细胞核大小,CEA标记,核分裂指数,瘤细胞密度指数）在两型之间差异存在显性和极限性。结论 新的胃癌病理-生物学分型揭示了肿瘤组织的生长活性和宿主的免疫防御反应在肿瘤生长和肿瘤侵袭方面的作用,在反映胃癌的生物学行为方面有重要意义。     

A Comparison Between Several Goodness of Fit Tests for Cox's Model

A comparison is made between two approaches to testing goodness of fit of Cox's regression model for survival data. The first approach is based on the inclusion of time dependent covariates, whereas the second one is based on the autocovariance of successive contributions to the derivative of the loglikelihood. It appears that the second test is most appropriate for testing in situations where the structure of the departure from proportional hazards is not known a priori. An approximate expression for the relative efficiency of the two test procedures is presented.     

A Simple, Reliable, and Fast Protocol for Thraustochytrid DNA Extraction

DNA extraction of thraustochytrids, common marine unicellular organisms, is usually accomplished by either the cetyltrimethylammonium bromide (CTAB) or proteinase K protocols. A novel lysis buffer protocol for thraustochytrid total DNA extraction is described. The average isolated total DNA is 20 to 40 kb, and DNA samples are suitable for a variety of uses including 18S–ribosomal DNA polymerase chain reaction, restriction enzyme digestions, and amplified fragment length polymorphism analyses. The new protocol is also faster than the other protocols. Received July 31, 2000; accepted November 2, 2000.     

A Simple Phenological Model of Muskmelon Development

Utilizing information gathered in previous growth chamber andfield experiments, we developed a simple temperature-drivencrop phenology model of muskmelon (Cucumis melo L.) to helpcommercial growers time crop phenological events and predictharvest dates. The model quantifies vegetative development interms of main vine node numbers which allows the model to simulateeither a direct-seeded or a transplanted crop. The model operateson an hourly time-step but requires only daily weather dataand a few cultivar-specific parameters including plastochroninterval and thermal time requirements to reach six predefineddevelopmental stages. The model was tested against an independentdata set consisting of three muskmelon cultivars grown at fivetransplanting dates. Tests of the model indicate an averageability to predict main vine node numbers to within one to twonodes of observed values. Estimated harvest date predictionswere more variable than those for main vine node number butan average model accuracy of 1 to 3 d was obtained in modeltests with a data set used to construct the model. Proceduresfor calibrating the model for different cultivars, culturalpractices or environments are outlined. Copyright 0000 Cucumis melo L., cantaloupe, temperature, model, thermal time, plastochron interval, growth duration     

A Simple Dynamic Model of Respiratory Pump

To study the interaction of forces that produce chest wall motion, we propose a model based on the lever system of Hillman and Finucane (J Appl Physiol 63(3):951–961, 1987) and introduce some dynamic properties of the respiratory system. The passive elements (rib cage and abdomen) are considered as elastic compartments linked to the open air via a resistive tube, an image of airways. The respiratory muscles (active) force is applied to both compartments. Parameters of the model are identified in using experimental data of airflow signal measured by pneumotachography and rib cage and abdomen signals measured by respiratory inductive plethysmography on eleven healthy volunteers in five conditions: at rest and with four level of added loads. A breath by breath analysis showed, whatever the individual and the condition are, that there are several breaths on which the airflow simulated by our model is well fitted to the airflow measured by pneumotachography as estimated by a determination coefficient R ² ≥ 0.70. This very simple model may well represent the behaviour of the chest wall and thus may be useful to interpret the relative motion of rib cage and abdomen during quiet breathing.     

Trends of classification,incidence, mortality,and survival of MDS patients in Switzerland between 2001 and 2012

Myelodysplastic syndromes (MDS) are emerging disorders of the elderly with an increasing burden on healthcare systems. He we report on the first population-based, epidemiological analysis of patients diagnosed with MDS in Switzerland between 2001 and 2012. The aim of this study was to characterize the extent and limitations of currently available population-based, epidemiological data and formulate recommendations for future health services research. The investigated outcomes comprised trends of annual case frequency, classification of morphological subtypes, incidence, mortality and survival. Annual case frequency increased by 20% (from 263 to 315 cases per year), whereas age-standardized incidence-/mortality-rates remained stable (2.5/1.1 per 100′000 person-years). This observation reflects population growth as well as higher diagnostic awareness and not an increase of age-specific risk. However, it will inevitably influence the future prevalence of MDS and the impact on healthcare systems. Reporting of classification in MDS subtypes was poor with modest improvement from 20% to 39% and increased awareness for mainly higher-risk diseases. Relative survival for all patients at 5-years (RS) ranged between 37 and 40%. Significant better RS was found for younger compared to older higher-risk MDS patients (48% vs. 17%), reflecting the effect of allogeneic hematopoietic stem-cell transplantation. However, no survival advantage was found in elderly patients after introduction of hypomethylating agents as standard for care in this patient group. Our data is in line with results from other MDS and cancer registries. It allows formulating recommendations for future collaborative health services research on MDS patients with national and international partners.     

Cox回归模型在肝癌病人生存分析中应用的研究

生存时间是癌症患者和临床医师共同关心的焦点,也是临床癌症诊治工作的重要指标之一．生存分析是研究多种因素与生存时间的关系以及关系程度的大小．Cox回归模型是生存分析中常用的方法之一．本文利用Cox回归模型对786名肝癌患者进行生存分析,确定影响肝癌患者预后的主要因素是癌栓、肝癌部位、治疗方式、肝脏储备功能、端粒酶活性、细胞增殖活性、γ-GT(γ-谷氮酰转肽酶)、术后复发等．为临床研究延长肝癌病人的生存期,提高其生存率提供了有力的依据．