An Asymptotic Analysis of the Logrank Test

Asymptotic expansions for the null distribution of the logrank statistic and its distribution under local proportional hazards alternatives are developed in the case of iid observations. The results, which are derived from the work of Gu (1992) and Taniguchi (1992), are easy to interpret, and provide some theoretical justification for many behavioral characteristics of the logrank test that have been previously observed in simulation studies. We focus primarily upon (i) the inadequacy of the usual normal approximation under treatment group imbalance; and, (ii) the effects of treatment group imbalance on power and sample size calculations. A simple transformation of the logrank statistic is also derived based on results in Konishi (1991) and is found to substantially improve the standard normal approximation to its distribution under the null hypothesis of no survival difference when there is treatment group imbalance. This revised version was published online in July 2006 with corrections to the Cover Date.     

A new mixture model for capture heterogeneity

Summary.  We propose a mixture of binomial and beta–binomial distributions for estimating the size of closed populations. The new mixture model is applied to several real capture–recapture data sets and is shown to provide a convenient, objective framework for model selection. The new model is compared with three alternative models in a simulation study, and the results shed light on the general performance of models in this area. The new model provides a robust flexible analysis, which automatically deals with small capture probabilities.     

配合尺寸公差中心范围加工法的应用与研究

目前机械加工企业根据国际标准偏差加工工件，由于受操作者主观因素的影响，工艺能力下降，工程等级降低，不能满足产品质量的要求，而配合尺寸公差中心范围加工法则很好地解决了这一问题。笔者论述了机为加工的质量特征分析，通过实例论证了配合尺寸公差中心范围加工法与传统加工方法的优越性与可行性。     

Gamers’ confidants: Massively Multiplayer Online Game participation and core networks in China

Through a survey of more than 18,000 participants in a Chinese Massively Multiplayer Online Game (MMOG), this study examines how the size and diversity of Chinese gamers’ core networks vary by individuals’ sociodemographic, socioeconomic and game-related characteristics. It represents the first study focusing exclusively on the gamer population and one of the most recent examining personal networks in contemporary China, home to over 560 million Internet users. We found that Chinese gamers have notably larger and more diverse core networks than those of major studies. Coplaying patterns and attachment to the game community contributed significantly to network size and diversity.     

中国上市公司监事会规模和构成的影响因素

理论分析表明,监事会规模及构成内生于公司风险。文章构建联立方程模型实证考察了监事会规模和构成的影响因素,在控制了内生性和制度因素影响后发现：公司经营范围、监督收益对监事会规模和职工监事比例有显著正向影响;监督成本、管理者权力对监事会规模和职工监事比例有显著负向影响。还发现：在控制了监事会规模和构成的影响因素后,监事会规模和职工监事比例与公司风险并没有统计意义上的相关性,表明监事会未能有效发挥降低公司风险的治理作用。因此,加强监事会能力建设,推进公司治理体系和治理能力现代化,仍将是中国公司治理改革努力的方向。     

基于小样本的安全第一投资组合优化模型

为了解决小样本情况下安全第一投资组合选择问题,将结构风险最小化原则引入投资组合选择过程中。根据结构风险最小化原则的直接实现,构建了含有范数约束的安全第一投资组合优化模型,并研究了模型参数的选取方法。实验结果验证了本模型的有效性。     

我国种植业经营主体发展趋势

通过对欧美日等3种不同人地禀赋国家农业经营实践经验的总结,结合我国保障粮食安全和农民增收的政策目标以及人地禀赋特征,认为我国农业将呈现分化发展的趋势,表现为既有适度规模经营主体结合社会化服务组织经营粮棉油等土地利用型作物,降低成本,应对国际市场竞争;又有小规模农户利用合作组织经营蔬菜、水果等劳动密集型产品,挖掘农产品附加价值,提高收入水平。基于2007年和2012年全国农产品成本收益数据研究表明：土地利用型产品的单产和价格上升空间有限,提高经营规模是降低产品单位成本、增加农民收入的重要途径;劳动密集型产品在无法提高经营规模的情况下,通过产后商品化处理、品牌化建设,提高产品附加值的潜力较大。     

Exact calculation of power and sample size in bioequivalence studies using two one‐sided tests

The number of subjects in a pharmacokinetic two‐period two‐treatment crossover bioequivalence study is typically small, most often less than 60. The most common approach to testing for bioequivalence is the two one‐sided tests procedure. No explicit mathematical formula for the power function in the context of the two one‐sided tests procedure exists in the statistical literature, although the exact power based on Owen's special case of bivariate noncentral t‐distribution has been tabulated and graphed. Several approximations have previously been published for the probability of rejection in the two one‐sided tests procedure for crossover bioequivalence studies. These approximations and associated sample size formulas are reviewed in this article and compared for various parameter combinations with exact power formulas derived here, which are computed analytically as univariate integrals and which have been validated by Monte Carlo simulations. The exact formulas for power and sample size are shown to improve markedly in realistic parameter settings over the previous approximations. Copyright © 2014 John Wiley & Sons, Ltd.     

关键审计事项披露对企业创新投入的影响

以2016—2019年2826家A股上市公司为样本,研究了关键审计事项披露对企业创新投入的影响。结果发现,关键审计事项披露对企业创新投入具有显著的正向影响。进一步研究发现,董事会效率在关键审计事项披露与企业创新投入之间具有部分中介作用;监事会规模对关键审计事项与企业创新投入二者关系具有负向调节作用;在不同供应链集中度的企业中,关键审计事项披露对企业创新投入的影响具有异质性。据此,建议企业管理层积极分析关键审计事项,帮助利益相关者全面准确了解关键审计事项的相关内容;企业董事会及监事会充分把握与注册会计师沟通的机会,提高企业创新投入的决策能力及监督能力。     

合理商品流通规模形成机制研究

合理商品流通规模的质的含义 ,是指商品流通规模的大小能够使商品流通系统经营服务能力达到最大化 ,并能够使国民经济系统处于良性循环的运动状态。合理商品流通规模量的含义 ,是指商品流通规模的大小必须适合社会再生产过程中各种因素所能承受的数量界限的可能性。商品流通规模合理化的指标体系由总量标准、结构标准和效率标准三大部分组成。商品流通规模扩张的动力结构 ,由原生动力、直接动力和间接动力组成。商品流通规模的调节机制 ,则由自我调节机制和宏观调节机制组成。