Testing equality of variances in the analysis of repeated measurements

The problem of comparing the precisions of two instruments using repeated measurements can be cast as an extension of the Pitman-Morgan problem of testing equality of variances of a bivariate normal distribution. Hawkins (1981) decomposes the hypothesis of equal variances in this model into two subhypotheses for which simple tests exist. For the overall hypothesis he proposes to combine the tests of the subhypotheses using Fisher's method and empirically compares the component tests and their combination with the likelihood ratio test. In this paper an attempt is made to resolve some discrepancies and puzzling conclusions in Hawkins's study and to propose simple modifications.
The new tests are compared to the tests discussed by Hawkins and to each other both in terms of the finite sample power (estimated by Monte Carlo simulation) and theoretically in terms of asymptotic relative efficiencies.     

The Bioeconomics of Marine Sanctuaries

Consider an offshore fishing grounds of size K. Suppose the grounds has been overfished to the point that net revenue has been driven to zero and the fishery is in open access equilibrium at (X, Y). A marine sanctuary, where fishing is prohibited, is then created. Suppose the marine sanctuary is of size K₂ and that fishing is allowed on a smaller grounds, now of size K₁, where K₁ + K₂ = K. In the first, deterministic, model, the present value of net revenue from the grounds-sanctuary system is maximized subject to migration (diffusion) of fish from the sanctuary to the grounds. The size of the sanctuary is varied, the system is re-optimized, and the populations levels, harvest, and value of the fishery is compared to the 'no-sanctuary' optimum, and the open access equilibrium. In the deterministic model, a marine sanctuary reduces the present value of the fishery relative to the 'ideal' of optimal management of the original grounds. In the second model net growth is subject to stochastic fluctuation. Simulation demonstrates the ability of a marine sanctuary to reduce the variation in biomass on the fishing grounds. Variance reduction in fishable biomass is examined for different-sized sanctuaries when net growth on the grounds and in the sanctuary fluctuate independently and when they are perfectly correlated. For the stochastic model of this paper, sanctuaries ranging in size from 60 to 40% of the original grounds (0.6 K₂/K 0.4) had the ability to lower variation in fishable biomass compared to the no sanctuary case. For a sanctuary equal to or greater than 70% of the original grounds (K₂ 0.7K), net revenue would be nonpositive and there would be no incentive to fish.     

Time diversification and security preferences: A stochastic dominance analysis

We use stochastic dominance to test whether investor should prefer riskier securities as the investment horizon lengthens. Return distributions for stocks, bonds, and U.S. Treasury bills are generated for holding periods of one to 25 years by simulation. For each holding period, stochastic dominance tests are run to establish preferences between the alternative security classes. Contrary to previous mean-variance based studies, we find no evidence that high-risk securities (stocks) dominate low-risk securities (bonds, Treasury bills) as the investment horizon lengthens. However, we do find that corporate bonds systematically dominate government bonds.     

Modified efficient importance sampling for partially non‐Gaussian state space models

The construction of an importance density for partially non‐Gaussian state space models is crucial when simulation methods are used for likelihood evaluation, signal extraction, and forecasting. The method of efficient importance sampling is successful in this respect, but we show that it can be implemented in a computationally more efficient manner using standard Kalman filter and smoothing methods. Efficient importance sampling is generally applicable for a wide range of models, but it is typically a custom‐built procedure. For the class of partially non‐Gaussian state space models, we present a general method for efficient importance sampling. Our novel method makes the efficient importance sampling methodology more accessible because it does not require the computation of a (possibly) complicated density kernel that needs to be tracked for each time period. The new method is illustrated for a stochastic volatility model with a Student's t distribution.     

人口规模与教育资源配置良性互动机制的动态仿真

我国人口规模与教育资源配置形成了恶性循环。以社会宏观动力学为分析框架, 基于2000—2019年面板数据,采用Vensim PLE软件,构建人口规模与教育资源配置互动机制系统动力学模型。研究表明：2024年开始,人口规模下降速度将逐年加快,教育市场将出现结构性萎缩,教育资源投入总量和速度将提高;人口规模对生产水平敏感;教育资源市场配置对人口增速、权力巩固程度、权力中心化程度、物力教育资源敏感。基于研究结论,提出两者良性互动的调适策略：保持经济高质量发展,降低生育养育成本;将生育权还给家庭,全面放开生育;巩固“双减”政策成效,引导教育需求;降低权力中心化程度,利用教育市场优势;加大教育资源投入,促进优质教育资源均衡。     

Investment planning under uncertainty and flexibility: the case of a purchasable sales contract*

Investment decisions are not only characterised by irreversibility and uncertainty but also by flexibility with regard to the timing of the investment. This paper describes how stochastic simulation can be successfully integrated into a backward recursive programming approach in the context of flexible investment planning. We apply this hybrid approach to a marketing question from primary production which can be viewed as an investment problem: should grain farmers purchase sales contracts which guarantee fixed product prices over the next 10 years? The model results support the conclusion from dynamic investment theory that it is essential to take simultaneously account of uncertainty and flexibility.     

行业异质性、适度知识产权保护与出口技术进步

本文将受知识产权保护制度约束的模仿效应参数及模仿成本引入Hausman的技术水平模型,通过建立1994—2009年SITC Rev.3的三位编码产品与中国国民经济中35个工业行业的对应关系,构建了行业出口技术水平测算指标,运用固定效应模型与系统GMM估计方法,实证分析了知识产权保护对行业出口技术进步的影响及在不同行业间的差异性体现。研究结果表明:中国知识产权保护制度的完善对出口技术提升起到了加速器的作用,但并未对出口规模扩张做出显著直接贡献,而是通过影响出口技术间接作用于出口规模;不同行业的知识属性差异使知识产权保护的出口技术进步效应在研发强度大、技术水平高、外资渗透率高的行业中更显著。     

县(市)级土地利用总体规划中耕地需求量预测方法及其应用

科学准确地预测耕地需求量,是制定县(市)级土地利用总体规划的基础.文章根据中国南方某县1996-2005年来的耕地变更调查统计数据,分别采用趋势分析法、回归分析法、指数平滑法、GM(1,1)模型法和灰色-马尔柯夫链模型的方法,对该地区耕地总量进行了模拟和预测.不同方法的预测结果表明,基于灰色-马尔柯夫链方法的预测结果更加准确可靠,更有利于土地管理决策者的经济决策行为.在当前耕地利用方式的背景下,灰色-马尔柯夫链模型可以作为县(市)级土地利用总体规划中耕地需求量预测方法的一种好选择.     

A forecast simulation analysis of the next‐generation DVD market based on consumer preference data

Just as standards wars over formats had characterized VCRs upon introduction to the market, the next‐generation DVD standards war between Blu‐Ray and HD‐DVD lasted 6 years before Blu‐Ray won the contest. Beginning with stated preference data drawn from a structured conjoint survey conducted before Blu‐Ray became the de facto standard of the next‐generation DVD format, we estimate consumer preferences on digital video players. A Bayesian mixed‐logit model is used and market share simulations are conducted under various scenarios based on the estimated parameters from Bayesian mixed‐logit model to surmise the future South Korean digital video‐player market. Results indicate that consumers feel that network size and title availability are more important than hardware‐related facets of the product, such as definition and storage capacity. The level of title availability and price of the Blu‐Ray player for Blu‐Ray's dominance over DVD will dramatically vary by the penetration rate of DVD players.     

仿真环境下企业能力测评方法及模型构建研究

能力测评是研究企业能力形成和演化机理的重要工具,是企业能力多主体仿真系统的重要功能模块。本文从构建复杂适应性主体角度,通过主体属性和行为定义模拟企业运行。重点将指标体系设计作为市场主体属性内容加以定义,在市场主体和能力主体的仿真运行过程中统计相关数据,按照预设关键指标算法,计算输出企业能力水平值,从量化角度评价企业能力大小。