VaR模型在人民币汇率风险度量中的应用

本文首先从VaR模型的假设前提入手,通过对人民币汇率收益率序列的随机性、正态性和异方差性的综合检验,验证了VaR模型在人民币汇率风险度量中的适用性.随后,分别采用非参数法和参数法两大类共九种VaR方法对人民币汇率风险进行实证度量.最后,通过准确性检验发现,GARCH-t模型是度量当前人民币汇率风险的最优方法.     

Ranking Crop Yield Models: A Comment

This comment discusses key specification issues that may have affected the performance and, therefore, the ranking of parametric models that were compared in a recent AJAE article. A procedure to obtain the most flexible parametric model specification possible, given the particular probability distribution function on which the model is based is presented. These specifications also allow for standardized and, therefore, more valid comparisons across parametric models that are based on different probability distributions. Finally, the comment cautions against generalization of the rankings in that AJAE article and recommends that these more flexible specifications be adopted in future comparisons and applications.     

生产率增长测算的半参数估计方法:理论综述和相关探讨

半参数模型是参数和非参数回归模型的一种概括统一，其中的参数分量部分用于对确定性影响因素进行分析，而非参数分量部分则用于对随机干扰因素的刻画。Olley和Pakes最早给出了关于生产率增长测算的半参数估计方法的研究，Ackerberg和Caves对这一研究进行了修正和补充。但由于理论发展方面还不够成熟，限制了方法的实证应用。半参数方法对经济现实的描述更接近真实，随着半参数估计理论的日渐成熟，半参数估计方法在生产率增长测算领域必将发挥越来越大的作用。     

中国数字化产业竞争力的区域差异与影响效应

本文从规模优势和发展潜力两个维度,提出数字化产业竞争力的测度方法,并以中国上市公司企业数据为基础,探讨区域层面的差异特征;利用半参数模型,从区域与行业双重层面,探究技术创新在数字化产业竞争力提升进程中的影响效应。研究发现：首先,当前中国数字化产业竞争力显著提升,但整体上呈现出由东部沿海向西部内陆递减的阶梯化分布特征,差异突出体现在规模优势层面。其次,技术创新对数字化产业竞争力的提升整体上存在倒U型影响效应,且表现出区域和行业差异。一方面,不同于东部地区,技术创新在中西部地区对数字化产业竞争力发挥着显著的正向推动作用;另一方面,不同于数字化服务业,技术创新对数字化制造业竞争力提升具有持续驱动效应。进一步分析表明,数字化制造业和数字化服务业耦合协调度处于较低的非均衡性状态。     

Designing and evaluating sustainable development pathways for semi‐subsistence crop–livestock systems: lessons from Kenya

Achieving the Sustainable Development Goals (SDGs) in African agriculture requires a better understanding why high levels of poverty and resource degradation persist in African agriculture despite decades of policy interventions and development projects. In this article, we hypothesize that policies need to account for the key features of the semi‐subsistence crop–livestock systems (CLS) in the region to become effective. The semi‐subsistence CLS are characterized by a high degree of biophysical and economic heterogeneity and a complex, diversified production system involving a combination of subsistence and cash crops with livestock. We investigated the potential for interventions proposed by the Government of Kenya to meet the SDGs by 2030. The analysis uses an integrated modeling approach designed to deal with the key features of these systems. A strategy that stimulates rural development, increases farm size to a sustainable level, and reduces distortions and inefficiencies in input and output markets could lead to a sustainable development pathway and achieve the SDGs for rural households dependent on CLS.     

复杂非限定约束曲面造型

文章介绍了两种曲面建构方法,并阐述了使用ISDX构造自由曲面模型的特点、方法和注意事项,指出了构造自由曲面模型和参数化曲面模型的最大区别是对曲率表的使用方式。     

债务期限结构和区域因素——来自中国上市公司的经验证据

本文采用参数和非参数检验方法经验检查中国上市公司注册地所在区域因素与公司债务期限结构之间关系。研究发现：（1）不同区域之间的债务期限结构存在系统性差异：（2）区域因素能解释公司债务期限结构3％左右的变异；（3）中部地区的债务期限显著高于东部、西部地区的债务期限；（4）市场化程度高、经济发达的地区具有相对低的债务期限。     

The Lognormal Distribution as a Model for Survival Time in Cancer, With an Emphasis on Prognostic Factors

Despite their long history, parametric survival-time models have largely been neglected in the modern biostatistical and medical literature in favour of the Cox proportional hazards model. Here, I present a case for the use of the lognormal distribution in the analysis of survival times of breast and ovarian cancer patients, specifically in modelling the effects of prognostic factors. The lognormal provides a completely specified probability distribution for the observations and a sensible estimate of the variation explained by the model, a quantity that is controversial for the Cox model. I show how imputation of censored observations under the model may be used to inspect the data using familiar graphical and other technques. Results from the Cox and lognormal models are compared and shown apparently to differ to some extent. However, it is hard to judge which model gives the more accurate estimates. It is concluded that provided the lognormal model fits the data adequately, it may be a useful approach to the analysis of censored survival data.     

A discrete and a continuous-time model based on a technical trading rule

In this article we propose a model in discrete and continuoustime that incorporates explicitly a technical trading rule inthe specification of the volatility. The proposed discrete-timemodel is an alternative to GARCH-type processes. We derive conditionsfor the covariance and strict stationarity of the discrete-timeprocess and we study the estimation and inference problems.We also analyze the conditions under which the discrete-timeprocess converges in distribution to a diffusion process. Toillustrate the proposed model and compare it with the GARCHspecification, we analyze the daily closing stock prices oftwo major U.S. companies (Microsoft and Oracle), two stock indices(DAX and NASDAQ) and two U.S. Dollar exchange rates (Euro andSterling)     

乡村用地规划碳源参数化评估模型

针对目前碳源评估研究主要集中在国家、省、城市层面,而乡村层面的研究十分有限,且大多数现有评估方法难以适用于乡村这种开放的、大尺度的系统等问题,构建了一套面向乡村用地规划的碳源参数化评估模型。该模型包括碳源评估清单的构建、碳排放因子的估算、基于调整系数的碳源评估公式的提出、参数化评估系统的搭建这4个关键环节,对此提出了一系列详细的技术方法。最后,通过一个多情景比较的实际规划案例说明了该模型的应用方法,体现其科学性和高效性,该模型可为低碳乡村规划提供一个实用的定量化工具。