Frequentist model averaging for linear mixed-effects models

Linear mixed-effects models are a powerful tool for the analysis of longitudinal data. The aim of this paper is to study model averaging for linear mixed-effects models. The asymptotic distribution of the frequentist model average estimator is derived, and a confidence interval procedure with an actual coverage probability that tends to the nominal level in large samples is developed. The two confidence intervals based on the model averaging and based on the full model are shown to be asymptotically equivalent. A simulation study shows good finite sample performance of the model average estimators.     

基于可拓变换的商业模式创新研究——以电动汽车商业模式创新为例

商业模式创新是企业本源的创新,是企业一切创新活动的基础和盈利的保障.目前,学术界和实业界对于商业模式创新仍然缺乏有效的方法和工具,在回顾商业模式相关文献的基础上,以电动汽车产业的商业模式创新为例,通过基元理论和可拓变换理论建立了流程化、形式化的商业模式创新方法.研究不仅丰富了商业模式理论,为商业模式创新提供了新的方法,同时对于丰富完善管理可拓工程理论也具有重要的意义.     

考虑退货的电商平台销售策略

本文研究当存在无缺陷退货时,电商平台如何选择合适的销售模式。根据销售价格和退货价格对市场需求以及退货的影响,电商平台可以策略性地选择转售模式和代理模式。我们构建了一个斯塔克伯格博弈模型,电商平台作为领导者选择销售模式,制造商在既定销售模式下进行决策。研究发现,当需求对价格的敏感程度较低、需求对退货价的敏感程度较高及退货量对退货价的敏感程度较低时,平台应提供代理模式,反之应提供转售模式,并探究平台的最优销售策略对制造商利润的影响,从而对平台和制造商的销售策略选择起到一定的指导意义。     

Comparative evaluation of various frequentist and Bayesian non-homogeneous Poisson counting models

In this paper a comparative evaluation study on popular non-homogeneous Poisson models for count data is performed. For the study the standard homogeneous Poisson model (HOM) and three non-homogeneous variants, namely a Poisson changepoint model (CPS), a Poisson free mixture model (MIX), and a Poisson hidden Markov model (HMM) are implemented in both conceptual frameworks: a frequentist and a Bayesian framework. This yields eight models in total, and the goal of the presented study is to shed some light onto their relative merits and shortcomings. The first major objective is to cross-compare the performances of the four models (HOM, CPS, MIX and HMM) independently for both modelling frameworks (Bayesian and frequentist). Subsequently, a pairwise comparison between the four Bayesian and the four frequentist models is performed to elucidate to which extent the results of the two paradigms (‘Bayesian vs. frequentist’) differ. The evaluation study is performed on various synthetic Poisson data sets as well as on real-world taxi pick-up counts, extracted from the recently published New York City Taxi database.     

基于结构方程模型的市场细分方法应用研究

结构方程模型是当前研究顾客满意和顾客忠诚的主流方法之一,但基于结构方程对顾客满意和顾客忠诚进行市场细分方法的研究却十分缺乏.基于结构方程模型进行市场细分算法的应用研究,并对得出的细分结果进行了解释.     

Modelling and simulation in business and industry: insights into the processes and practices of expert modellers

The simulation modelling process and individual practices of simulation modellers impact on the outcome of simulation studies. Despite this, the modelling and simulation literature lacks a rich body of evidence on the actual process and practices of modellers in the real world. This qualitative study aims to address this shortcoming by attempting to discover the underlying simulation modelling process of 20 expert modellers working within their typical contexts. Our study makes a valuable addition to simulation research by investigating how the expert modellers develop their simulation models and how their context may affect their simulation practices. The main finding is that most of the participants do not have a clearly defined or a formal process for developing their models. Instead, they follow a set of key steps and their individual practices depend on the context of the study. A number of contextual factors such as the term of model use, the size of the model and the complexity of the model, may affect the way in which a modeller goes about developing a simulation model. For instance, the extent to which a model is documented depends on the model life. This research contributes to enhancing our understanding of the simulation modelling process in varying contexts.     

基于动态损失厌恶投资组合优化模型及实证研究

为了研究行为金融学中损失厌恶的心理特征对投资决策的影响,建立预期效用最大化的动态损失厌恶投资组合优化模型。以我国股票市场为依托进行实证研究,将市场分为上升、下降和盘整三种状态,研究动态损失厌恶投资组合模型的表现,与静态损失厌恶投资组合模型、均值-方差投资组合模型和CVaR投资组合模型进行比较。通过改变参照点对动态模型进行稳健性检验。得出动态损失厌恶投资组合模型优于静态模型、均值-方差投资组合模型和CVaR投资组合模型的结论。     

A fractional tumor-growth model and the determination of the power law for different cancers based on data fitting

We study a fractional model for tumor growth and derive its general solution, the blow-up time and the radius of convergence. The model is simplified then to fit human data. The results show that there is a noticeable variation in the value of the scaling exponent depending on whether the model is fractional or integer. This supports the idea that the inclusion of memory effects may become relevant in the study of tumor growth via the scaling exponent.     

An individual-based stochastic model of the spread of tuberculosis

Under study is an individual-based stochastic model of the spread of tuberculosis. We present a probability theory formalization of the model which rests on a characterization of individuals in distinct groups (uninfected, infected, and sick people). Some results of computational experiments concern the selecting parameters of the model based on approximation of actual data. We study how the distributions of the sizes of the groups change in dependence on the variation of the parameters of the model.     

Conceptual modelling for simulation Part I: definition and requirements

Conceptual modelling is probably the most important aspect of a simulation study. It is also the most difficult and least understood. Over 40 years of simulation research and practice have provided only limited information on how to go about designing a simulation conceptual model. This paper, the first of two, discusses the meaning of conceptual modelling and the requirements of a conceptual model. Founded on existing literature, a definition of a conceptual model is provided. Four requirements of a conceptual model are described: validity, credibility, utility and feasibility. The need to develop the simplest model possible is also discussed. Owing to a paucity of advice on how to design a conceptual model, the need for a conceptual modelling framework is proposed. Built on the foundations laid in this paper, a conceptual modelling framework is described in the paper that follows.     

A two species competition model under the simultaneous effect of toxicant and disease

A mathematical model is proposed to study the simultaneous effects of toxicants and infectious diseases on a competing species system. It is assumed that the competing populations are adversely affected by the toxicant and one of them is vulnerable to an infectious disease. In this paper, two models are studied separately. The first model is developed to study the effect of only infectious diseases on the existence of a two competing species system in the absence of a toxicant, whereas in the second model the presence of a toxicant is also taken into account. In both the models, conditions for the existence of interior equilibria are derived. The models are analyzed using stability theory, and conditions for the nonlinear stability of the interior equilibria are obtained using Lyapunov’s direct method. Further, the models are studied numerically by taking two sets of numerical values for each model and the results are compared.     

On Large Time Behavior and Selection Principle for a Diffusive Carr–Penrose Model

This paper is concerned with the study of a diffusive perturbation of the linear LSW model introduced by Carr and Penrose. A main subject of interest is to understand how the presence of diffusion acts as a selection principle, which singles out a particular self-similar solution of the linear LSW model as determining the large time behavior of the diffusive model. A selection principle is rigorously proven for a model which is a semiclassical approximation to the diffusive model. Upper bounds on the rate of coarsening are also obtained for the full diffusive model.     

On a mathematical model for laser-induced thermotherapy

We study a mathematical model for laser-induced thermotherapy, a minimally invasive cancer treatment. The model consists of a diffusion approximation of the radiation transport equation coupled to a bio-heat equation and a model to describe the evolution of the coagulated zone. Special emphasis is laid on a refined model of the applicator device, accounting for the effect of coolant flow inside. Comparisons between experiment and simulations show that the model is able to predict the experimentally achieved temperatures reasonably well.     

A bottom-up biofuel market equilibrium model for policy analysis

Although the biofuel market remains at its early stage, it is expected to play an important role in climate policy in the future in the transportation sector. In this paper, we develop a bottom-up equilibrium model to study the supply chain of the biofuel market, explicitly formulating the interactions among farmers, biofuel producers, blenders, and consumers. The model is built on optimization problems faced by each entity and considers decisions associated with farmers’ land allocation, biomass transportation, biofuel production, and biofuel blending. As such, the model is capable of and appropriate for policy analysis related to interactions among multiple stakeholders. For example, the model can be used to analyze the impacts of biofuel policies on market outcomes, pass-through of taxes or subsidies, and distribution of consumers’ or producers’ surplus. The equilibrium model can also serve as an analytical tool to study the price impact of biomass, biofuel, and Renewable Identification Numbers (RINs) for biofuels. We demonstrate the model by applying it to a case study of Iowa. We specifically focus on the effects of market structure, i.e., points-of-implementation on subsidies on market outcomes. The results indicate that some entities can benefit greatly at the expense of others when they possess market power. Government oversight is therefore needed to safeguard the development of the sector.     

A constitutive model for the flow stress behavior and microstructure evolution in aluminum alloys under hot working conditions – with application to AA6099

A constitutive model for aluminum alloys under hot working conditions is proposed. The elastic-viscoplastic model is implemented in a finite strain continuum mechanical framework. The model accounts for the interplay between dynamic recovery and recrystallization during hot working of aluminum alloys and central aspects of microstructure evolution such as grain/subgrain size and dislocation density. The proposed model is generic in the sense that it can be used for arbitrary aluminum alloys, but in order to demonstrate its capabilities, the model is calibrated to a newly developed AA6099 alloy in the present study. The model is thoroughly discussed and details on the numerical implementation as well as on the calibration of the model against experimental data are provided.     

A general framework for frequentist model averaging In Celebration of Professor Lincheng Zhao's 75th Birthday

Model selection strategies have been routinely employed to determine a model for data analysis in statistics, and further study and inference then often proceed as though the selected model were the true model that were known a priori. Model averaging approaches, on the other hand, try to combine estimators for a set of candidate models. Specifically, instead of deciding which model is the 'right' one, a model averaging approach suggests to fit a set of candidate models and average over the estimators using data adaptive weights.In this paper we establish a general frequentist model averaging framework that does not set any restrictions on the set of candidate models. It broaden, the scope of the existing methodologies under the frequentist model averaging development. Assuming the data is from an unknown model, we derive the model averaging estimator and study its limiting distributions and related predictions while taking possible modeling biases into account.We propose a set of optimal weights to combine the individual estimators so that the expected mean squared error of the average estimator is minimized. Simulation studies are conducted to compare the performance of the estimator with that of the existing methods. The results show the benefits of the proposed approach over traditional model selection approaches as well as existing model averaging methods.     

Nonlinear dynamical analysis and demonstration on Chinese business cycle

This paper is devoted to the study of a generalized Chinese business cycle by nonlinear dynamical method. Firstly, we establish a Chinese economic cycle model based on Goodwin model, and then discuss the point estimation and confidence interval of the model’s parameter values based on the historical data. At last, we study the bifurcation and chaotic behavior of the model. The results show that the marginal consumption has great influence on the development of Chinese economic. The Chinese economic development will run into the stable periodic wave when the marginal consumer is greater than 0.5. Furthermore, the greater the marginal consumption is, the more stable the economic development is.     

Full backward non-homogeneous semi-Markov processes for disability insurance models: A Catalunya real data application

In this paper a stochastic model for disability insurance contracts is presented. The model is based on a discrete time non-homogeneous semi-Markov process to which the backward recurrence time process is joined. This permits us to study in a more complete way the disability evolution and to face the duration problem in a more effective way. The model is applied to a sample of contracts drawn at random from a mutual insurance company.