Estimation of discrete survival function for error‐prone diagnostic tests

The product limit or Kaplan‐Meier (KM) estimator is commonly used to estimate the survival function in the presence of incomplete time to event. Application of this method assumes inherently that the occurrence of an event is known with certainty. However, the clinical diagnosis of an event is often subject to misclassification due to assay error or adjudication error, by which the event is assessed with some uncertainty. In the presence of such errors, the true distribution of the time to first event would not be estimated accurately using the KM method. We develop a method to estimate the true survival distribution by incorporating negative predictive values and positive predictive values, into a KM‐like method of estimation. This allows us to quantify the bias in the KM survival estimates due to the presence of misclassified events in the observed data. We present an unbiased estimator of the true survival function and its variance. Asymptotic properties of the proposed estimators are provided, and these properties are examined through simulations. We demonstrate our methods using data from the Viral Resistance to Antiviral Therapy of Hepatitis C study.     

简单平均组合预测有效性的应用分析

通过实例分析,说明了当序列模式变动较大时,简单平均组合预测模型相对于其他组合预测模型的优越性,并且基于样本段的拟合精度不足以说明组合预测模型的外推预测精度。文中的分析对于组合预测模型的选择和应用具有实际参考价值。     

词义关系与英语写作

英语写作学习中,学习者写出的短文经常是词不达意,错误百出,缺乏生动与准确。究其原因,学习者词汇量有限,词义知之甚少是造成这些问题的主要障碍。但如果英语学习者能借助词义关系来扩大词汇量、正确掌握词义,他们驾驭词汇的能力必将提高,制约英语写作能力的词汇问题会迎刃而解,并使英语写作的表达更为生动与准确。     

结构一能动性干扰：问卷调查精度的局限性分析

以往对于问卷调查精度的探讨通常局限在“访问员“受访者”或“研究者”的三维关系当中,或专门针对问卷本身进行技术改良,很少注意到与这三者紧密相关的社会环境因素。以人为客体的社会领域研究不同于自然科学,势必会受到社会环境因素的干扰。而在问卷调查过程当中,影响调查精度最深的社会性因素是行政管理结构,这一结构性因素贯穿于问卷调查的始末,在这一结构作用下,行政管理者可以依附结构力量,能动地对问卷调查的结果产生影响,引导问卷结果偏向更加有利的一面,通过对以往研究过程当中所遇到的此类现象进行综合分析,总结出行政管理者所采用的四种能动性影响方式,从而探讨其对问卷调查的影响。最终,将这一影响问卷调查结果的现象称为“结构一能动性干扰”,并认为这一因素可能造成问卷结果在很大程度上会偏离真实,而对这一问题的解决,难以简单从以往三维关系或问卷技术改良上得到改善。     

A permutation test approach to the choice of size k for the nearest neighbors classifier

The k nearest neighbors (k-NN) classifier is one of the most popular methods for statistical pattern recognition and machine learning. In practice, the size k, the number of neighbors used for classification, is usually arbitrarily set to one or some other small numbers, or based on the cross-validation procedure. In this study, we propose a novel alternative approach to decide the size k. Based on a k-NN-based multivariate multi-sample test, we assign each k a permutation test based Z-score. The number of NN is set to the k with the highest Z-score. This approach is computationally efficient since we have derived the formulas for the mean and variance of the test statistic under permutation distribution for multiple sample groups. Several simulation and real-world data sets are analyzed to investigate the performance of our approach. The usefulness of our approach is demonstrated through the evaluation of prediction accuracies using Z-score as a criterion to select the size k. We also compare our approach to the widely used cross-validation approaches. The results show that the size k selected by our approach yields high prediction accuracies when informative features are used for classification, whereas the cross-validation approach may fail in some cases.     

A sequential conditional probability ratio test procedure for comparing diagnostic tests

In this paper, we derive sequential conditional probability ratio tests to compare diagnostic tests without distributional assumptions on test results. The test statistics in our method are nonparametric weighted areas under the receiver-operating characteristic curves. By using the new method, the decision of stopping the diagnostic trial early is unlikely to be reversed should the trials continue to the planned end. The conservatism reflected in this approach to have more conservative stopping boundaries during the course of the trial is especially appealing for diagnostic trials since the end point is not death. In addition, the maximum sample size of our method is not greater than a fixed sample test with similar power functions. Simulation studies are performed to evaluate the properties of the proposed sequential procedure. We illustrate the method using data from a thoracic aorta imaging study.     

高校教师教育技术能力的成熟度模型

高校教师教育技术能力成熟度的研究是高校信息化评估研究的子集,也是教育技术和教育管理研究的前沿和热点问题。本研究在吸收国内外研究成果的基础上,对比分析已有的评估模式,依据教育信息化评估模型E2M2(e-Edu-cation maturity model)和《我国国家高校教师教育技术能力指南》,分析这些研究成果存在的不足,提出以成熟度模型为特点的诊断性评估方式。该模型作为一种诊断性评估工具由5个一级指标和17个二级指标项组成,每个指标项包括5个成熟度等级。     

基于任务的英语学习者口语准确性和流利性对比研究

对不同任务类型(复述故事和即席讲话)中29名英语学习者口语准确性和流利性的关系调查和分析表明,在复述故事中,口语准确性和流利性没有显著的相关性;在即席讲话中,口语准确性和流利性呈低度或低中度相关。t检验表明,复述故事中口语准确性显著低于即席讲话中口语准确性;流利性随测量指标的不同在任务之间呈现不同的差异模式。     

Impact of Reseller's Forecasting Accuracy on Channel Member Performance

This article studies a three‐layer supply chain where a manufacturer sells a product through a reseller who then relies on its own salesperson to sell to the end market. The reseller has superior capability in demand forecasting relative to the manufacturer. We explore the main trade‐offs between the risk‐reduction effect and the information–asymmetry–aggravation effect of the improved forecasting accuracy. We show that under the optimal wholesale price contract, both the manufacturer and the reseller are always better off as the reseller's forecasting accuracy improves. Nevertheless, under the menu of two‐part tariffs, the manufacturer prefers the reseller to be either uninformed or perfectly informed about the market condition. We further find that the improved forecasting accuracy is beneficial for the reseller if its current forecasting system is either very poor or very good.     

The forecast accuracy of Australian Bureau of Statistics national population projections

This paper examines the forecast accuracy of Australian Bureau of Statistics national population projections produced from the 1960s to the early 2000s. As well as total populations, the accuracy of the following is assessed: age-sex-specific populations, the Total Fertility Rate, life expectancy at birth and net international migration. It is shown that forecasts of the 1960s and 70s were the most inaccurate; forecasts of the 1980s and later proved to be much more reliable. The paper goes on to take an alternative perspective on population forecast error through the use of an adapted percentage error measure which accounts for offsetting errors in births, deaths, net migration and the jump-off population. This measure also permits an assessment of the relative contributions of the components of demographic change to overall inaccuracy. It is shown that errors in forecasting net international migration have generally contributed most to inaccuracy followed by births and then deaths and jump-off error. ABS projections of total population are also compared to those produced using a simple naïve model. The paper concludes by arguing that the new error measure could prove valuable in other studies of population forecast accuracy.