A worldwide analysis of trend in crop yields and yield variability: Evidence from FAO data

The trend in crop yields and yield variability affects food security and impact agricultural and food policies. Recent studies in this area have either focused only on one country or performed global analysis on a handful of crops. We provide the first worldwide analysis of trend and variability for 8088 country-crop yield series taken from the FAO database, employing a robust estimator to cope with the adverse statistical effects of outliers. More than half of the series display a slowdown in yield growth due to a closing of the gap between realised and attainable yields as well as to agricultural policies promoting more sustainable agricultural practices. Around one fourth of the series show also an increase in yield variability as a consequence of climate change and changes in farm management practices. Yield variability is highest in Eastern Europe, Central Asia and Middle East and North Africa, where food security may be threatened.     

基于Hill估计的VaR计算——以次贷危机为例

对极值分布的尾部形式、Hill估计量、风险价值分析等进行了理论分析,应用极值理论中的Hill估计对2002-01-04至2008-09-18期间的上证综指、道琼斯指数、恒生指数等做了风险价值的计算,比较和分析各国面临的市场风险的大小：认为美国次贷危机的爆发给全球金融市场带来了巨大风险,对中国的影响尤为巨大。     

Combining information for prediction in linear regression

This article deals with the prediction problem in linear regression where the measurements are obtained using k different devices or collected from k different independent sources. For the case of k=2, a Graybill-Deal type combined estimtor for the regression parameters is shown to dominate the individual least squares estimators under the covariance criterion. Two predictors ŷ _c and ŷ _p are proposed. ŷ _c is based on a combined estimator of the regression coefficient vector, and ŷ _p is obtained by combining the individual predictors from different models. Prediction mean square errors of both predictors are derived. It is shown that the predictor ŷ _p is better than the individual predictors for k≥2 and the predictor ŷ _c is better than the individual predictors for k=2. Numerical comparison between ŷ _c and ŷ _p shows that the former is superior to the latter for the case k=2.     

中国通货膨胀率持久性变化研究及政策含义分析

通胀率持久性在通胀率动态研究中备受学界的关注,并且直接影响现代货币政策传导机制的终解方程式。本文对我国通胀率持久性的统计特性做了严谨的计量检验和分析,应用“格点拔靴(自举)”中值无偏估计和Exp-Wald未知断点检验来捕捉我国物价波动持久性的特征。统计结果显示,通胀率持久性在高通胀时期走高,而在物价波动减小的20世纪90年代中后期显著减弱。我们讨论了这一发现对相关货币政策分析机制的含义。     

非等间隔动态面板数据模型：估计方法与应用实例

非等间隔动态面板数据模型由于相邻两期观测之间的时间长度不尽相同使得传统动态面板数据模型的估计方法失效,本文提出使用非线性最小二乘、最短距离以及它们的一步估计量对该模型进行估计,证明了这四个估计量的一致性和渐进正态性,同时借助蒙特卡洛模拟的方法验证了它们在有限样本中的估计精度,并且进一步使用所提出的估计量讨论了以往文献由于缺乏相应的估计方法而没有被研究或者充分讨论的问题,得到了一些新的结论。     

Expectations Formation and Risk in Three Financial Markets: Surveying What the Surveys Say

This paper attempts to provide a logical overview of the literature which exploits survey data to examine issues of expectations formation and risk aversion in financial markets. Our survey suggests that: short term expectations are excessively volatile and exhibit bandwagon effects, while longer term expectations appear to be regressive and therefore stabilising; in bond and foreign exchange markets the standard result of forward rate biasedness is due in part to time-varying premia; recent research using disaggregate foreign exchange survey data demonstrates the importance of heterogeneous expectations.     

信用风险模型的贝叶斯改进研究

基于小样本数据和外部先验信息,本文运用贝叶斯(Bayes)估计量来改进信用风险模型的违约预测力。同时,运用中国上市公司财务数据,分别对贝叶斯估计量和标准Logit估计量进行了模拟估计,并通过统计量AUC值和布莱尔分数(Brier Score)对其预测精度进行比较。结果表明,贝叶斯估计量具有更高的预测精度和稳定性。     

Intra-Industry Trade: A Static and Dynamic Panel Data Analysis

This study examines the features and determinants of intra-industry trade (IIT), horizontal IIT (HIIT) and vertical IIT (VIIT) between Portugal and the European Union in the period 1996–2002, using a static and a dynamic panel data analysis. The findings indicate that Portuguese VIIT increased significantly during the period in accordance with the values expected for a developed country. The regression results show that there is evidence supporting the explanation of VIIT by Heckscher–Ohlin’s (HO) theory and that Portugal has comparative advantages in low-quality differentiated products. The findings support the theory that, in general, there is no positive statistical association between HIIT and HO variables. The central theme of this paper is to show that it may be preferable to use the GMM approach in empirical studies of IIT rather than pooled OLS, fixed effects or random effects estimators. The results also suggest that the GMM system estimator obtains more reasonable parameter estimates than the first-differenced GMM estimator.

一种基于代价函数的正交频分复用中符号同步与频偏估计算法

本文利用正交频分复用（OFDM）帧结构的特点，引入代价函数，推导出了一种符号同步算法和频偏估计算法，并从理论上分析了在存在频偏的情况下，符号同步可以独立于频偏估计。计算机仿真表明，该算法具有较好的同步和频偏估计性能。     

金融开放与银行风险承担的异质性研究——基于98个国家的实证分析

金融开放是加剧银行业风险还是分散风险,是颇具争议的研究课题。本文借助Gygli et al.(2018)的金融开放指标,应用1999-2016年98个国家的跨国数据,检验了金融开放和银行风险承担的长期均衡和短期关系。从长期均衡关系来看,金融开放显著地提高了银行抵御风险能力,具有长期"促进效应";从短期关系来看,金融开放则存在一定"风险效应"①。进一步研究发现,短期"风险效应"与外资银行资产占比不存在关联,而与市场制度环境显著相关,即完善的制度环境有助于弱化"风险效应"。结合中国实际情况,文章支持"以开放促改革"的观点,强调完善市场制度环境的重要性,为政策制定者提供实证依据。