QMRA for Drinking Water: 2. The Effect of Pathogen Clustering in Single‐Hit Dose‐Response Models

Spatial and/or temporal clustering of pathogens will invalidate the commonly used assumption of Poisson‐distributed pathogen counts (doses) in quantitative microbial risk assessment. In this work, the theoretically predicted effect of spatial clustering in conventional “single‐hit” dose‐response models is investigated by employing the stuttering Poisson distribution, a very general family of count distributions that naturally models pathogen clustering and contains the Poisson and negative binomial distributions as special cases. The analysis is facilitated by formulating the dose‐response models in terms of probability generating functions. It is shown formally that the theoretical single‐hit risk obtained with a stuttering Poisson distribution is lower than that obtained with a Poisson distribution, assuming identical mean doses. A similar result holds for mixed Poisson distributions. Numerical examples indicate that the theoretical single‐hit risk is fairly insensitive to moderate clustering, though the effect tends to be more pronounced for low mean doses. Furthermore, using Jensen's inequality, an upper bound on risk is derived that tends to better approximate the exact theoretical single‐hit risk for highly overdispersed dose distributions. The bound holds with any dose distribution (characterized by its mean and zero inflation index) and any conditional dose‐response model that is concave in the dose variable. Its application is exemplified with published data from Norovirus feeding trials, for which some of the administered doses were prepared from an inoculum of aggregated viruses. The potential implications of clustering for dose‐response assessment as well as practical risk characterization are discussed.     

A Bayesian hierarchical approach to dual response surface modelling

In modern quality engineering, dual response surface methodology is a powerful tool to model an industrial process by using both the mean and the standard deviation of the measurements as the responses. The least squares method in regression is often used to estimate the coefficients in the mean and standard deviation models, and various decision criteria are proposed by researchers to find the optimal conditions. Based on the inherent hierarchical structure of the dual response problems, we propose a Bayesian hierarchical approach to model dual response surfaces. Such an approach is compared with two frequentist least squares methods by using two real data sets and simulated data.     

Optimal designs for response functions with a downturn

In many toxicological assays, interactions between primary and secondary effects may cause a downturn in mean responses at high doses. In this situation, the typical monotonicity assumption is invalid and may be quite misleading. Prior literature addresses the analysis of response functions with a downturn, but so far as we know, this paper initiates the study of experimental design for this situation. A growth model is combined with a death model to allow for the downturn in mean doses. Several different objective functions are studied. When the number of treatments equals the number of parameters, Fisher information is found to be independent of the model of the treatment means and on the magnitudes of the treatments. In general, A- and D_A-optimal weights for estimating adjacent mean differences are found analytically for a simple model and numerically for a biologically motivated model. Results on c-optimality are also obtained for estimating the peak dose and the EC₅₀ (the treatment with response half way between the control and the peak response on the increasing portion of the response function). Finally, when interest lies only in the increasing portion of the response function, we propose composite D-optimal designs.     

国际石油价格波动对我国宏观经济的影响——基于VAR的实证研究

石油价格波动是牵动一国经济领域方方面面的要素之一,备受各国政府的关注。通过建立描述国际石油价格波动与我国工业生产总值(GIP)、生产者价格指数(PPI)之间动态关系的向量自回归模型,研究国际石油价格波动对我国宏观经济的影响。脉冲响应分析的结果显示:石油价格上涨会使我国的通货膨胀加剧,国际石油价格与我国GIP增长率的相关性还需进一步考证,而高油价并没有在短期内改变中国经济增长的基本趋势。     

构建高校基层党组织回应机制的必要性与路径

构建高校基层党组织回应机制是培育新一代大学生党员、探索高校基层党建模式、不断丰富马克思主义执政党建设理论的需要。当前,构建高校基层党组织回应机制的制约因素主要是:回应动力不足、回应渠道不畅通与回应载体缺乏创新。为此,需要建立制度化的互动模式、畅通回应渠道、推进回应载体信息化建设。     

后危机时代“弃企逃债”的反思与应对

国际金融危机暴发后,不少地方不同程度出现“弃企逃债”现象并产生一定不良后果。究其原因,既有一些企业及企业主破产心理变态、破产理念失当问题,也有破产生态不良、破产制度硬伤问题。为此,后危机时代应疏导破产心理、确立正确破产观、改善破产生态环境、完善破产法律制度,最大限度、地避免“弃企逃债”,以维护经济秩序,减少社会震动。     

我国服务业与服务贸易发展协同性的实证分析

选取4个影响服务业发展的因素和决定服务贸易的2个因素,建立VAR模型,分析我国服务业与服务贸易发展二者之间的关系。通过Granger因果分析和脉冲响应函数的实证研究,得出现阶段我国服务业与服务贸易之间尚未形成良性的协调发展机制,即服务业与服务贸易之间不存在相互促进的关系。     

“犯案老手”与“侦案神探”——论阿加莎·克里斯蒂侦探小说的设悬与释悬

阿加莎·克里斯蒂作品中悬念设置的主要技巧和方法:一是倒置设悬;二是连环设悬;三是隐形人设悬以及运用哑谜、切隔、反常、危局等方法来故布疑阵,营造氛围。由此说明成功设置悬念能给读者提供多层面的审美参与,成功的侦探小说可以承担起文学的多种审美功能。     

一类离散非自治捕食模型持久性与周期解的存在性

主要讨论一类具有IV类功能反应的离散非自治捕食模型,利用比较原理和重合度理论,获得了其持久性和周期解的存在性的充分条件。     

Is the medium the message? Perceptions of and reactions to crisis communication via twitter, blogs and traditional media

Value changes and the rapid emergence of media innovations (internet, social web) in society lead to an institutionalization of crisis communication, in which especially new media play a crucial role. The key contributions of the paper include deepening and refocusing the theoretical foundations of crisis communication by experimentally analyzing the effects of traditional and social-media strategies on the recipients’ perceptions of reputation; and by analyzing the effects or crisis responses on the recipients’ secondary crisis communications (e.g., sharing information and leaving a message) and reactions (e.g., willingness to boycott). The results indicated that the medium matters more than the message. For all three dependent measures - reputation, secondary crisis communication and reactions - main effects of medium occurred, whereas the message had only a significant main effect on secondary crisis reactions.