复杂产品系统合作创新契约模型有效性研究

合作创新是复杂产品系统模块化生产的重要手段,但模块研制中的利益外部性和隐藏检查行为使合作单位易发生道德风险损害项目效益。通过不完全契约激励模型的构建和分析,对模块分包模式和联合研制模式契约模型在合作单位激励约束机制上的有效性进行了探讨。研究表明,模块分包模式中合作单位不承担系统集成风险,因此惩罚金和完全竞争不能抑制道德风险的发生;而联合研制模式使利益外部性内部化,从而避免合作单位道德风险的发生,保证了合作创新的有效性。     

Testing a covariance matrix: exact null distribution of its likelihood criterion

For X～ N _p (μ, Σ) testing H _o:Σ = Σ ₀, with Σ ₀ known, relies at present on an approximation of the null-distribution of the likelihood ratio statistic.

We present here the exact null distribution and also its computation, hence providing a precise tool that can be used in small sample cases.     

Testing equality of correlation coefficients for paired binary data from multiple groups

Paired binary data arise naturally when paired body parts are investigated in clinical trials. One of the widely used models for dealing with this kind of data is the equal correlation coefficients model. Before using this model, it is necessary to test whether the correlation coefficients in each group are actually equal. In this paper, three test statistics (likelihood ratio test, Wald-type test, and Score test) are derived for this purpose. The simulation results show that the Score test statistic maintains type I error rate and has satisfactory power, and therefore is recommended among the three methods. The likelihood ratio test is over conservative in most cases, and the Wald-type statistic is not robust with respect to empirical type I error. Three real examples, including a multi-centre Phase II double-blind placebo randomized controlled trial, are given to illustrate the three proposed test statistics.     

Flexible parametric modelling of the hazard function in breast cancer studies

In cancer research, study of the hazard function provides useful insights into disease dynamics, as it describes the way in which the (conditional) probability of death changes with time. The widely utilized Cox proportional hazard model uses a stepwise nonparametric estimator for the baseline hazard function, and therefore has a limited utility. The use of parametric models and/or other approaches that enables direct estimation of the hazard function is often invoked. A recent work by Cox et al. [6 Cox, C., Chu, H., Schneider, M. F. and Munoz, A. 2007. Parametric survival analysis and taxonomy of hazard functions for the generalized gamma distribution. Stat. Med., 26: 4352–4374. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] has stimulated the use of the flexible parametric model based on the Generalized Gamma (GG) distribution, supported by the development of optimization software. The GG distribution allows estimation of different hazard shapes in a single framework. We use the GG model to investigate the shape of the hazard function in early breast cancer patients. The flexible approach based on a piecewise exponential model and the nonparametric additive hazards model are also considered.     

Continuous covariate frailty models for censored and truncated clustered data

Using some logarithmic and integral transformation we transform a continuous covariate frailty model into a polynomial regression model with a random effect. The responses of this mixed model can be ‘estimated’ via conditional hazard function estimation. The random error in this model does not have zero mean and its variance is not constant along the covariate and, consequently, these two quantities have to be estimated. Since the asymptotic expression for the bias is complicated, the two-large-bandwidth trick is proposed to estimate the bias. The proposed transformation is very useful for clustered incomplete data subject to left truncation and right censoring (and for complex clustered data in general). Indeed, in this case no standard software is available to fit the frailty model, whereas for the transformed model standard software for mixed models can be used for estimating the unknown parameters in the original frailty model. A small simulation study illustrates the good behavior of the proposed method. This method is applied to a bladder cancer data set.     

出生人口性别比周期性波动研究——兼论中国出生人口性别比的变化趋势

在观察数据基础上,描述出生人口性别比周期性波动现象,并对其内在机理做出解释。研究发现,出生人口性别比的周期性波动是一个普遍规律,其波动周期与生育间隔相关。正常情况下,周期成分对出生人口性别比的变化影响较小并且稳定。中国出生人口性别比的周期成分明显大于其他国家,这与中国强烈的性别偏好有关。周期成分不是影响中国出生人口性别比的主要因素,性别选择行为是出生人口性别比失衡的主要原因。在实际工作中应该尊重出生人口性别比周期性波动的客观规律,关注出生人口性别比的中长期变化趋势。中国出生人口性别比的"拐点"已经出现,在继续加强综合治理工作的条件下,出生人口性别比将进入下降过程。     

外来人口对中国城市地区出生性别比的影响

外来人口对中国城市地区出生性别比的影响是近年来学术界争论的焦点问题之一。利用2000年人口普查数据,通过比较农村本地人口、城市本地人口和城市外来人口三个人口群体在出生性别比上的差异,并进行多元统计分析,考察20世纪90年代以来中国城市地区异常偏高的出生性别比是否由外来人口造成?结果表明,城市外来人口生育的性别偏好与农村本地人口和城市本地人口相比没有显著差异,都存在强烈的生男意愿。20世纪90年代以来中国生育水平迅速下降的同时,出生性别比出现了不分城乡的普遍升高和偏高,城市出生性别比偏高,既有外来人口的作用,也有本地人口的作用,外来人口并不是造成中国城市地区出生性别比偏高的唯一或主要的原因。     

Risk Assessment and Alternatives Assessment: Comparing Two Methodologies

The selection and use of chemicals and materials with less hazardous profiles reflects a paradigm shift from reliance on risk minimization through exposure controls to hazard avoidance. This article introduces risk assessment and alternatives assessment frameworks in order to clarify a misconception that alternatives assessment is a less effective tool to guide decision making, discusses factors promoting the use of each framework, and also identifies how and when application of each framework is most effective. As part of an assessor's decision process to select one framework over the other, it is critical to recognize that each framework is intended to perform different functions. Although the two frameworks share a number of similarities (such as identifying hazards and assessing exposure), an alternatives assessment provides a more realistic framework with which to select environmentally preferable chemicals because of its primary reliance on assessing hazards and secondary reliance on exposure assessment. Relevant to other life cycle impacts, the hazard of a chemical is inherent, and although it may be possible to minimize exposure (and subsequently reduce risk), it is challenging to assess such exposures through a chemical's life cycle. Through increased use of alternatives assessments at the initial stage of material or product design, there will be less reliance on post facto risk‐based assessment techniques because the potential for harm is significantly reduced, if not avoided, negating the need for assessing risk in the first place.     

应用型本科院校师资队伍建设的现状、 问题与对策

应用型本科院校的特殊性决定了应用型本科院校教师应具有自身特性.审视我国应用型本科院校师资队伍在生师比、职称结构、学历/学位结构、年龄结构、实践教学和专/兼职教师等方面的现状及存在的问题,提出多渠道大力引进教师,调适师资队伍结构;加强教师培训,促进教师专业发展;完善评聘机制,使“双师型”教师脱颖而出等对策建议.     

基于任务跟踪的在线租赁问题与竞争策略研究

现实经济活动中,有许多租赁融资决策既非纯在线租赁问题也非纯离线租赁问题,而是介于二者之间的具有部分已知信息的在线租赁问题.基于此研究了工作任务总量已知而工作任务进展序列未知的在线设备租赁问题,以租赁工作所需设备的费用最小为优化目标,建立了该问题的基本数学模型,提出了任务跟踪策略,给出并证明了基于这一策略的算法的竞争比.最后,把该在线租赁问题的竞争比与经典的在线租赁问题的竞争比做了比较分析,结果表明在线租赁问题的算法优于经典的在线算法,竞争性能得到了较大的提高.