Do Drivers of Small Cars Take Less Risk in Everyday Driving?

Previously reported observed data on risky everyday driving are brought together and reanalyzed in order to focus on the relation between risky driving and the size of the car being driven, as indicated by car mass. The measures of risky driving include separation between vehicles in heavy freeway traffic and speed on a two lane road. Observed seat belt use provides a third measure of driver risk. Confounding effects arising from the observed association between car mass and driver age are taken into account by segmenting the data into three driver age groups. Driver risk taking is found to increase with increasing car mass for each of these three aspects of everyday driving. The implications of these results with respect to driver fatality rates are discussed in terms of a simple model relating observed risky driving to the likelihood of involvement in a severe crash.     

Who captures the marks for the Petersen estimator?

Summary.  We examine the claim that the well-known Petersen estimator which is used in population size estimation was not in fact used by the scientist after whom it is named. We show how, in the early years of the last century, the modern use of the Petersen estimator grew from that of the fishing coefficient. Contending with the somewhat conflicting claims that were made at the time, and what by modern standards is poor referencing of sources, we investigate where the credit lies for these concepts, and the principles and protocols which support them. We assess also how far attributions of credit were affected by practical considerations, and the history of the estimator by the nature of the problems being pursued. We identify scientists whose early work on marking and estimating fish populations deserves more credit than it has received.     

Non-parametric estimation of population size from capture–recapture data when the capture probability depends on a covariate

Summary.  In capture–recapture experiments the capture probabilities may depend on individual covariates such as an individual's weight or age. Typically this dependence is modelled through simple parametric functions of the covariates. Here we first demonstrate that misspecification of the model can produce biased estimates and subsequently develop a non-parametric procedure to estimate the functional relationship between the probability of capture and a single covariate. This estimator is then incorporated in a Horvitz–Thompson estimator to estimate the size of the population. The resulting estimators are evaluated in a simulation study and applied to a data set on captures of the Mountain Pygmy Possum.     

试论清朝满蒙联姻政策的特点及其积极影响

满蒙联姻政策是清朝民族政策一个最为重要的组成部分,同前代相比,清朝的满蒙联姻具有制度性以及大规模、多层次、持续性等特点。这种联姻政策所形成的姻亲关系,对满蒙两族的长期和好、对清廷统辖与治理边疆蒙古地区乃至利用蒙古族的军事力量,起到了重要的作用。同时对于促进满蒙汉各族在政治、经济、风俗文化各方面的互相融合也起到了不可忽视的积极作用。     

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.     

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。