Response predictions in regressions on panel data

In this paper we consider the problem of obtaining best linear unbiased estimators of individual response coefficients in a Random Coefficient Linear Regression (RCR} Model, comparing alternative estimators for these response vectors through a simulation study. We also provide an empirical example that illustrates the estimation procedure proposed here.     

Plans for blocking and fractions of nested cube designs

Plans for implementing nested cube designs invoiving 3 to 5 factors within moderate sized blocks are eveloped. Fractionsc of 1/2 and 1/4 replicates of components of the generic design are used. Suggestions for data analysis are offered.     

Conditions for fourth order rotatability in K dimensions

In this paper, conditions for a set of points to form a rotatable design of order four have been worked out. These condi- tions form the basis for obtaining a set of rotatable designs of order four.     

Recognizing Structural Nonidentifiability: When Experiments Do Not Provide Information About Important Parameters and Misleading Models Can Still Have Great Fit

In the quest to model various phenomena, the foundational importance of parameter identifiability to sound statistical modeling may be less well appreciated than goodness of fit. Identifiability concerns the quality of objective information in data to facilitate estimation of a parameter, while nonidentifiability means there are parameters in a model about which the data provide little or no information. In purely empirical models where parsimonious good fit is the chief concern, nonidentifiability (or parameter redundancy) implies overparameterization of the model. In contrast, nonidentifiability implies underinformativeness of available data in mechanistically derived models where parameters are interpreted as having strong practical meaning. This study explores illustrative examples of structural nonidentifiability and its implications using mechanistically derived models (for repeated presence/absence analyses and dose–response of Escherichia coli O157:H7 and norovirus) drawn from quantitative microbial risk assessment. Following algebraic proof of nonidentifiability in these examples, profile likelihood analysis and Bayesian Markov Chain Monte Carlo with uniform priors are illustrated as tools to help detect model parameters that are not strongly identifiable. It is shown that identifiability should be considered during experimental design and ethics approval to ensure generated data can yield strong objective information about all mechanistic parameters of interest. When Bayesian methods are applied to a nonidentifiable model, the subjective prior effectively fabricates information about any parameters about which the data carry no objective information. Finally, structural nonidentifiability can lead to spurious models that fit data well but can yield severely flawed inferences and predictions when they are interpreted or used inappropriately.     

Ebola Virus Dose Response Model for Aerosolized Exposures: Insights from Primate Data

This study develops dose–response models for Ebolavirus using previously published data sets from the open literature. Two such articles were identified in which three different species of nonhuman primates were challenged by aerosolized Ebolavirus in order to study pathology and clinical disease progression. Dose groups were combined and pooled across each study in order to facilitate modeling. The endpoint of each experiment was death. The exponential and exact beta-Poisson models were fit to the data using maximum likelihood estimation. The exact beta-Poisson was deemed the recommended model because it more closely approximated the probability of response at low doses though both models provided a good fit. Although transmission is generally considered to be dominated by person-to-person contact, aerosolization is a possible route of exposure. If possible, this route of exposure could be particularly concerning for persons in occupational roles managing contaminated liquid wastes from patients being treated for Ebola infection and the wastewater community responsible for disinfection. Therefore, this study produces a necessary mathematical relationship between exposure dose and risk of death for the inhalation route of exposure that can support quantitative microbial risk assessment aimed at informing risk mitigation strategies including personal protection policies against occupational exposures.     

A Simple Toxicokinetic Model Exhibiting Complex Dynamics and Nonlinear Exposure Response

Uncertainty in model predictions of exposure response at low exposures is a problem for risk assessment. A particular interest is the internal concentration of an agent in biological systems as a function of external exposure concentrations. Physiologically based pharmacokinetic (PBPK) models permit estimation of internal exposure concentrations in target tissues but most assume that model parameters are either fixed or instantaneously dose-dependent. Taking into account response times for biological regulatory mechanisms introduces new dynamic behaviors that have implications for low-dose exposure response in chronic exposure. A simple one-compartment simulation model is described in which internal concentrations summed over time exhibit significant nonlinearity and nonmonotonicity in relation to external concentrations due to delayed up- or downregulation of a metabolic pathway. These behaviors could be the mechanistic basis for homeostasis and for some apparent hormetic effects.     

The robustness of response surface designs with errors in factor levels

ABSRTACT

Since errors in factor levels affect the traditional statistical properties of response surface designs, an important question to consider is robustness of design to errors. However, when the actual design could be observed in the experimental settings, its optimality and prediction are of interest. Various numerical and graphical methods are useful tools for understanding the behavior of the designs. The D- and G-efficiencies and the fraction of design space plot are adapted to assess second-order response surface designs where the predictor variables are disturbed by a random error. Our study shows that the D-efficiencies of the competing designs are considerably low for big variance of the error, while the G-efficiencies are quite good. Fraction of design space plots display the distribution of the scaled prediction variance through the design space with and without errors in factor levels. The robustness of experimental designs against factor errors is explored through comparative study. The construction and use of the D- and G-efficiencies and the fraction of design space plots are demonstrated with several examples of different designs with errors.     

理性的分析是创作的基础—几个近作的创作探讨

本文是一篇基于理性分析的创作探讨，它通过实践说明，理性的思维是创作的基础，是迅速把握事物本质的捷径。理想的思维包括三个方面的内容：体验功能，感应环境，辩证地对待业主的意见。     

Risk Perception in an Interest Group Context: An Examination of the TMI Restart Issue1

Human response to environmental hazards and risks has been the subject of considerable research by social scientists. Work has traditionally focused on either individual response to the risks of an ongoing or future threat (hazards research), or group and organizational response to a specific disaster event (disaster research). As part of a larger investigation of the restart of the Unit 1 reactor at Three Mile Island (TMI), we examined the response of interest groups active in the restart issue to the continued threat of TMI and to future risks due to restart. After reviewing the restart issue in general, the paper examines the local dimensions of the restart issue from interest group perspectives. A method for defining appropriate issues at the community level is reviewed. We then discuss differences in the perceived local impacts of alternative decisions, and systems of beliefs associated with differing perceptions. Finally, we discuss the implications of interest group versus individual perceptions of local issues for decision making about TMI, in particular, and about technological hazards management, in general. Associated implications for determining socially acceptable risk levels are identified. Our research led us to three major conclusions: (1) in contrast to other types of hazards, interest groups are a critical unit of analysis for understanding how beliefs and behaviors form in response to the presence of technological hazards; (2) the divergence of positions between groups, even though they may have shared the same physical experience, is understandable if not always predictable, (3) the resolution of policy debates where risks are a major focus of the arguments should recognize the legitimacy of these divergent positions by allowing participation of the various interest groups in the decision process. Such participation helps ensure that the decision strategy is responsive to local concerns, thereby increasing the likelihood of acceptance of the ultimate decision and thus producing a publicly acceptable level of risk.     

超立方体计算机直通通信技术

对线路交换、消息交换、包交换,虚拟旁通和直通的平均通信延迟时间以及直通的平均请求响应时间进有了分析。比较指出,直通的平均通信延迟时间和平均请求响应时间最短。因此,直通通信技术在超级并行/分布计算机系统中,是克服互连和通信障碍的最有效的技术之一。