基于改进突变级数法的农产品物流产业评估模型研究

对农产品物流产业发展水平进行客观、准确的分析与评估,可为政府部门优化与调整产业发展、合理制定产业规划提供科学依据。运用突变级数法与离差最大化法构建农产品物流产业评估模型,并选取广东和山东两省20102014年相关数据对构建的评估模型进行实例分析。结果表明：广东省农产品物流产业发展的优势主要体现在信息化水平与经济基础两方面,基础设施建设则是当前制约其产业发展的关键因素;而庞大的产业规模是现阶段支撑山东省农产品物流产业发展的重要力量。改进的突变级数评估模型既克服了主观赋权的局限,又不失科学性和合理性,计算简单,具有重要实用价值。     

资产专用性对确权后农地流转的影响

农地确权后,农户对农地转出多持中立或否定的态度,这与产权明晰促进交易的产权理论大相径庭。文章探讨了资产专用性对确权后农地流转的作用机理,并运用吉林省9市1444个农户数据对其进行实证分析。结果表明：农地确权后,土地资产、农业资产、地理位置以及人力资本等专用性抑制农户转出农地,农业资产和人力资本专用性抑制农户提高农地租金,而社会资本专用性则分别存在促进作用;农业资产、地理位置以及人力资本等专用性抑制农户更长时间转出农地;农业资产专用性对转出农地须要签订合约具有抑制作用,而地理位置专用性则存在促进作用。     

结构优化对我国农产品出口竞争力的影响

应用产业组织理论,揭示结构优化对农产品国际竞争力的作用机理。以RCA衡量农产品出口竞争力并建立多元回归模型,在有效分离工资、土地灌溉面积和汇率等因素后,实证研究发现技术结构对农产品出口竞争力有显著正向影响。当前经济背景下,提升农产品出口竞争力的政策思路,需从传统的要素禀赋优势转移到结构优化的轨道上来。优化农产品出口结构,政府需加大对高附加值农产品在生产、流通、出口等环节的支持力度,营造寡占的农产品市场结构,鼓励和扶持创意农业的发展。     

美国粮食价格突变及其对国内农业安全的启示

美国粮食市场价格突变可能为我国农业安全带来不可估量的冲击。以玉米和大豆产业为例,选取2000—2013年季度价格相关数据,基于PPM模型识别了玉米和大豆价格突变节点并测算其形成原因。实证结果显示,自21世纪以来,全美玉米市场共发生了六次价格上升突变、两次价格下降突变;大豆市场则历经四次价格上升突变、两次价格下降突变。粮价突变是供需因素与国际贸易、原油价格、美元指数变动等众多非供需因素共同作用的结果,因所处政治经济背景不同,各阶段形成原因也不尽相同。分析表明,美国粮价突变首先通过价格信息与贸易渠道间接的影响国内玉米和大豆价格;然后经由其他农产品价格波动、短期供给波动、国际游资及外商控制等路径对国内农业安全带来威胁。     

Pooled Panel Unit Root Tests and the Effect of Past Initialization

This paper analyzes the role of initialization when testing for a unit root in panel data, an issue that has received surprisingly little attention in the literature. In fact, most studies assume that the initial value is either zero or bounded. As a response to this, the current paper considers a model in which the initialization is in the past, which is shown to have several distinctive features that makes it attractive, even in comparison to the common time series practice of making the initial value a draw from its unconditional distribution under the stationary alternative. The results have implications not only for theory, but also for applied work. In particular, and in contrast to the time series case, in panels the effect of the initialization need not be negative but can actually lead to improved test performance.     

Understanding Estimators of Treatment Effects in Regression Discontinuity Designs

In this paper, we propose two new estimators of treatment effects in regression discontinuity designs. These estimators can aid understanding of the existing estimators such as the local polynomial estimator and the partially linear estimator. The first estimator is the partially polynomial estimator which extends the partially linear estimator by further incorporating derivative differences of the conditional mean of the outcome on the two sides of the discontinuity point. This estimator is related to the local polynomial estimator by a relocalization effect. Unlike the partially linear estimator, this estimator can achieve the optimal rate of convergence even under broader regularity conditions. The second estimator is an instrumental variable estimator in the fuzzy design. This estimator will reduce to the local polynomial estimator if higher order endogeneities are neglected. We study the asymptotic properties of these two estimators and conduct simulation studies to confirm the theoretical analysis.     

On the Joint Estimation of Heterogeneous Technologies,Technical, and Allocative Inefficiency

In this article, we provide a semiparametric approach to the joint measurement of technical and allocative inefficiency in a way that the internal consistency of the specification of allocative errors in the objective function (e.g., cost function) and the derivative equations (e.g., share or input demand functions) is assured. We start from the Cobb–Douglas production and shadow cost system. We show that the shadow cost system has a closed-form likelihood function contrary to what was previously thought. In turn, we use the method of local maximum likelihood applied to a system of equations to obtain firm-specific parameter estimates (which reveal heterogeneity in production) as well as measures of technical and allocative inefficiency and its cost. We illustrate its practical application using data on U.S. electric utilities.     

The Local Power of the CADF and CIPS Panel Unit Root Tests

Very little is known about the local power of second generation panel unit root tests that are robust to cross-section dependence. This article derives the local asymptotic power functions of the cross-section argumented Dickey–Fuller Cross-section Augmented Dickey-Fuller (CADF) and CIPS tests of Pesaran (2007), which are among the most popular tests around.     

A Seemingly Unrelated Nonparametric Additive Model with Autoregressive Errors

This article considers a nonparametric additive seemingly unrelated regression model with autoregressive errors, and develops estimation and inference procedures for this model. Our proposed method first estimates the unknown functions by combining polynomial spline series approximations with least squares, and then uses the fitted residuals together with the smoothly clipped absolute deviation (SCAD) penalty to identify the error structure and estimate the unknown autoregressive coefficients. Based on the polynomial spline series estimator and the fitted error structure, a two-stage local polynomial improved estimator for the unknown functions of the mean is further developed. Our procedure applies a prewhitening transformation of the dependent variable, and also takes into account the contemporaneous correlations across equations. We show that the resulting estimator possesses an oracle property, and is asymptotically more efficient than estimators that neglect the autocorrelation and/or contemporaneous correlations of errors. We investigate the small sample properties of the proposed procedure in a simulation study.     

喷动床最小喷动速度的计算颗粒流体力学数值模拟

基于第二期“全国新型农业经营主体发展指数调查”中的706个合作社样本,采用OLS和Tobit方法分析了合作社经营绩效对其精准扶贫参与的影响及作用机制。研究表明:合作社经营绩效与精准扶贫参与之间存在显著的“U”型关系,在对模型进行改进和选择代理变量检验后结果依旧稳健。作用机制分析表明,合作社经营绩效与获取政府补贴和承担社会责任之间同样存在“U”型关系,后者正是合作社参与精准扶贫的动机所在。鉴于此,政府应加强对精准扶贫参与主体的核查,同时须支持合作社发展,以壮大其帮扶带动能力。