Some Cracks in the Empire of Chance (Flaws in the Foundations of Reliability)

Making quantified statements about the uncertainty associated with the lifelength of an item is one of the most fundamental tasks of reliability assessment. Most practitioners routinely do this using one of the several available statistical techniques. The purpose of this paper is two-fold. The first is to give the user an overview of the key tenets of two of the most commonly used parametric approaches. The second is to point out that these commonly used approaches involve strategies that are either ad hoc, or are in violation of some of the underlying tenets. A method that is devoid of logical flaws can be proposed, but this method is difficult to implement. The user must therefore resign to using that technique against which the fewest objections can be hurled.     

长白山区作物气候生产力及其地理分布的研究

本文建立了长白山区玉米、水稻和大豆的气候可能产量模式和地理分布模型,计算了各地的气候生产潜力,并进行了地形影响订正。结果表明,长白山区主要农作物气候生产力的地理分布特征主要取决于地势、地形和经度,气候生产力随着海拔的升高按照三次抛物线函数递减,随着经度的升高按照线性函数递减。主要山体的南、西南坡气候生产力较高,北、东北坡气候生产力较低。该项研究为长白山区农业立体开发提供了综合气候生态依据。     

基于模糊时间序列的预测模型——以上证指数为例

模糊理论使用语义变量本身所蕴含的特性,能减少处理问题时的不确定性所带来的困扰,被广泛的应用于各种领域的研究。首先回顾了基于模糊理论的模糊时间序列定义,对现有的模糊时间序列模型进行分析;在此基础上提出了一种新的模糊时间序列预测方法,以上证指数为对象进行了拟合。从结果看,新的基于模糊时间序列预测方法在MSN、平均误差(%)和标准误差(%)等指标上要优于现有的的预测方法。     

银行危机与货币危机共生性关系的实证研究

1 997— 1 998年的亚洲金融风暴中 ,银行危机与货币危机的同时爆发 ,即共生性危机的发生引发国际社会与学术界对这种现象的重新思考 :这种共生性现象是否确实具有普遍性 ?从理论的角度来看 ,银行危机与货币危机之间的确存在着一定的联系 ,但到目前为止 ,很少有研究从实证的角度来证明这种联系的确存在。正是基于此 ,本文从实证的角度出发 ,旨在揭示出银行危机与货币危机之间的确存在着相互影响 ,换言之 ,共生性危机的发生是具有显著性的。具体来说 ,本文以 1 975— 2 0 0 0年期间 53个国家危机的发生情况为研究对象 ,分别运用频率分布、信号法 ,以及概率回归模型来分析两种危机的共生性 ,并得到非常一致的结论 :在新兴市场国家中 ,银行危机与货币危机之间的确存在着明显的相互关系 ,同时银行危机更趋向于作为货币危机即将发生的同步或预警指标 ,而反之则不然。     

A New Approach to Random Utility Modeling using the Dirichlet Multinomial Distribution

In this paper we introduce a new econometricapproach to analyzing recreational site choicedata, the Dirichlet multinomial model. Thismodel, which nests the standard conditionalmultinomial logit model, can accommodateover-dispersed data and may provide moreefficient estimators of coefficients andconsequent welfare measures than the standardconditional logit model, which is so widelyused in the Random Utility Model approach torecreation demand. We illustrate thisDirichlet approach using a data set of rockclimbers in Scotland, and study the impacts onper-trip consumers surplus of alternativemanagement strategies for popular rock climbingsites. Results show that the Dirichletmultinomial approach produces coefficient andwelfare estimates having smaller samplingvariability in this case. We also compareclassical welfare measures with their posteriorequivalents, which allow for welfare changes tobe dis-aggregated.     

Some Reflections on the Spatial Dimensions of Occupational Segregation

This paper considers the role that urban spatial structure may play in the process of occupational segregation, and argues that neoclassical economic models of urban employment and residential location decisions have not considered the relationship between gender-based labor market status and space. The paper provides a critical feminist perspective on how conventional urban models have been used to explain patterns of segregation, and suggests reasons for limitations in existing theoretical and empirical analysis. It also explores ways in which economists can draw on work in other disciplines to develop fuller and more useful models of the relationship between urban spatial structure and occupational segregation.     

Reforming Social Security in a Transition Economy: The Case of Lithuania

This paper points out a number of problems associated with the existing pension system in Lithuania. Reforms are proposed, including (i) a substantial increase in the basic pension benefit rate, financed on a pay-as-you-go basis, provided universally, and regulated according to wage/price indexation; (ii) a significant cut in the tax contribution rate to the public pension system matched by a rise in the VAT; (iii) a rise in the retirement age to 65 for both men and women; and (iv) a gradual conversion to a private, funded, mandatory pension system to replace the earnings-related part of the current pension system.     

Nowcasting China’s GDP Using a Bayesian Approach

Real time nowcasting is an assessment of current-quarter GDP from timely released economic and financial series before the GDP figure is disseminated. Providing a reliable current quarter nowcast in real time based on the most recently released economic and financial monthly data is crucial for central banks to make policy decisions and longer-term forecasting exercises. In this study, we use dynamic factor models to bridge monthly information with quarterly GDP and achieve reduction in the dimensionality of the monthly data. We develop a Bayesian approach to provide a way to deal with the unbalanced features of the dataset and to estimate latent common factors. We demonstrate the validity of our approach through simulation studies, and explore the applicability of our approach through an empirical study in nowcasting the China’s GDP using 117 monthly data series of several categories in the Chinese market. The simulation studies and empirical study indicate that our Bayesian approach may be a viable option for nowcasting the China’s GDP.     

Scaling the volatility of GDP growth rates

The distribution of shocks to GDP growth rates is found to be exponential rather than normal. Their standard deviation scales with GDP^β where β=−0.15±0.03. These macroeconomic results place restrictions on the microeconomic structure of interactions between agents.     

Objective methods for graphical structural learning

Graphical models are used for expressing conditional independence relationships among variables by the means of graphs, whose structure is typically unknown and must be inferred by the data at hand. We propose a theoretically sound Objective Bayes procedure for graphical model selection. Our method is based on the Expected-Posterior Prior and on the Power-Expected-Posterior Prior. We use as input of the proposed methodology a default improper prior and suggest computationally efficient approximations of Bayes factors and posterior odds. In a variety of simulated scenarios with varying number of nodes and sample sizes, we show that our method is highly competitive with, or better than, current benchmarks. We also discuss an application to protein-signaling data, which wieldy confirms existing results in the scientific literature.