基于SARIMA-SVR组合模型的 空气质量指数预测

空气质量指数(AQI)在波动中既具有整体的时间序列线性特征和明显的季节性波动周期,又具有多种因素影响的不确定性,为了提高AQI的预测精度,基于Ri386 3.3.3和Matlab R2014a两种编程软件,提出了一种同时具有线性和非线性的复合特征的时间序列预测模型——SARIMA-SVR组合模型。以太原市2014年1月—2019年7月的AQI月均值数据为基础,利用SARIMA时间序列模型进行线性预测,利用SVR模型对残差进行非线性预测,加和得到组合预测模型的预测结果,分析比较SARIMA,SVR和SARIMA-SVR这3种模型的预测结果和平均绝对百分比误差。结果表明,组合预测模型发挥了2种模型各自的优势,相较于单一预测模型的预测结果而言,其预测精度更高,稳定性更好。通过此模型得到的空气质量预测结果不仅可为人们的日常生活提供指导,而且可为大气污染的防治工作提供科学依据和借鉴意义。     

On the Opportunity Cost of Crop Diversification

Distance functions are increasingly being augmented, with environmental goods treated as conventional outputs. A common approach to evaluate the opportunity cost of providing an environmental good is the exploitation of the distance function's dual relationship to the value function. This implies that the opportunity cost is assumed to be non‐negative. This approach also requires a convex technology set. Focusing on crop diversification for a balanced sample of 44 cereal farms in the East of England for the years 2007–2013, this paper develops a novel opportunity cost measure that does not depend on these strong assumptions. We find that the opportunity cost of crop diversification is negative for most farms.     

面源污染视角下江西省耕地利用效率研究

[目的]在面源污染视角下考察耕地利用效率,可以为推动耕地可持续利用提供理论和参考依据。[方法]文章基于2000—2014年我国13个粮食主产省(区)耕地投入产出的面板数据,运用SBM方向性距离函数将耕地面源污染因素纳入到传统的效率分析框架,从省际比较的维度对江西省耕地利用效率进行了测度与分析。[结果]考虑面源污染因素对耕地利用效率测算产生了一定的影响;江西省耕地利用效率值呈现阶段性特征,耕地利用效率排名比较稳定,近年来排名有上升趋势;江西省耕地利用绩效一般,且与最佳实践者存在较大的差距。[结论]忽视面源污染因素的耕地利用效率评估是失真和不符合实际的,宜将面源污染因素纳入到耕地利用效率的测度框架,以此来更科学地量化评估耕地利用绩效;设计和完善相关政策,以有效控制耕地面源污染;加强与先进省(区)的交流与合作,学习其农业可持续耕作技术与管理经验,进一步推动江西省耕地产出与资源、环境协调发展。     

粮食与经济重心迁移路径及空间耦合关系分析*——以湖北省粮食主产县为例

[目的]我国的粮食安全问题一直备受关注,作为粮食安全重要保障的粮食主产区近年来却面临着粮食生产与经济发展协调性、可持续性下降的困扰。文章以湖北省46个粮食主产县为研究区,对其粮食生产与经济发展的耦合协调状况进行研究,以期为地方政府粮食安全政策制定提供参考。[方法]以研究区粮食产量、地区生产总值、行政区划图层为数据源,构建重心模型和空间耦合模型,对粮食主产县2006—2015年间粮食重心和经济重心迁移路径、粮食生产与经济发展耦合协调状况进行分析。[结果](1)研究期间粮食主产县的粮食重心和经济重心整体上皆向西北方向转移,经济重心始终位于粮食重心东南部,经济重心的移动幅度大于粮食重心,但经济重心的移动方向更稳定。研究区北部的粮食生产地位高于南部,南部的经济地位则高于北部,粮食生产的稳定性相对低于经济发展。(2)两重心整体上虽均向西北方向转移,但具体移动方向存在较大差异,两者空间重叠性整体下降,变动一致性减弱,空间耦合性变差。(3)粮食生产与经济发展空间一致性地域分异特征明显,相较于2006年,2015年粮食经济整体协调性进一步减弱,粮食生产与经济发展日趋分散。[结论]建立重心模型和空间耦合模型对粮食生产与经济发展耦合协调状况进行研究是有效可行的,为推动粮食生产与经济发展协调稳步发展决策提供一定的参考。     

农户土地转出的影响因素研究*——基于土地流转补贴政策效用的视角

[目的]基于安徽省蚌埠市的调研数据,实证研究土地流转补贴政策对土地转出的影响,分析土地流转补贴政策效用。[方法]文章根据国内外相关研究成果,结合调研地区的具体环境因素,提出研究假设,选取农户的家庭人口特征、社会经济特征和土地资源禀赋等变量,构建回归模型,运用SPSS统计软件分析农户土地转出的影响因素及土地流转补贴政策的效用。[结果]直接影响农户土地转出的因素包括非农就业、非农收入、农民离乡进城务工条件和土地资源禀赋等,农民获得的土地流转补贴占家庭总收入的比重非常小,对农户转出土地的意愿起不到显著促进作用。[结论]因此,促进土地有序流转必须把土地流转补贴等财政扶持资金转移到基本生产设施的建设上,改善农业生产经营条件,增强新型农业经营主体的土地转入积极性;通过创造非农就业机会,增加非农收入,完善农村社会保障服务体系,促进农民工市民化等措施,弱化农民对土地的依赖,从而增强农民转出土地的积极性。     

The power of positivity? The influence of positive psychological capital language on crowdfunding performance

We extend the entrepreneurship literature to include positive psychological capital — an individual or organization's level of psychological resources consisting of hope, optimism, resilience, and confidence — as a salient signal in crowdfunding. We draw from the costless signaling literature to argue that positive psychological capital language usage enhances crowdfunding performance. We examine 1726 crowdfunding campaigns from Kickstarter, finding that entrepreneurs conveying positive psychological capital experience superior fundraising performance. Human capital moderates this relationship while social capital does not, suggesting that costly signals may, at times, enhance the influence of costless signals. Post hoc analyses suggest findings generalize across crowdfunding types, but not to IPOs.     

Inequality and entrepreneurial thresholds

We explore the relationship between inequality and entrepreneurial activity. Drawing on cross-sectional data from a largescale survey of the economic conditions of individuals across India, we develop a number of dimensions of inequality to explore empirically how inequality interacts with entrepreneurship, operationalized as self-employment or as employing other people. We find compelling evidence that there are thresholds to becoming self-employed, and even more so to assembling the combinations of resources and personal attributes required to become an employer. Greater inequality leaves more people unable to make the transition to self-employment, leaving casual laboring as the occupation of necessity. At the same time, inequality increases the number of employers in a society, by concentrating resources - particularly land and finance - enough for significant numbers of people to be able to cross this higher threshold. Lastly, greater differentiation into social or religious groups curtails the ability to cross either entrepreneurial threshold, presumably by limiting the extent and benefits of social networks of value for entrepreneurship.     

ECONOMIC POLICY UNCERTAINTY EFFECTS ON CREDIT AND STABILITY OF FINANCIAL INSTITUTIONS

We examine policy‐related economic uncertainty effects on the availability of credit, non‐performing loans and loan loss provisions using a panel of 18 countries. We provide significant evidence that uncertainty reduces the availability of credit while leading to increases in banks' non‐performing loans and loan loss provisions, distorting sectoral stability. Our findings are economically meaningful.     

Investor behaviour and reaching for yield: Evidence from the sterling corporate bond market

We provide evidence on how corporate bond investors react to a change in yields, and how this behaviour differs in times of market‐wide stress. We also investigate ‘reaching for yield’ across investor types, as well as providing insights into the structure of the corporate bond market. Using proprietary sterling corporate bond transaction data, we show that insurance companies, hedge funds and asset managers are typically net buyers when corporate bond yields rise. Dealer banks clear the market by being net sellers. However, we find evidence for this behaviour reversing in times of stress for some investors. During the 2013 ‘taper tantrum’, asset managers were net sellers of corporate bonds in response to a sharp rise in yields, potentially amplifying price changes. At the same time, dealer banks were net buyers. Finally, we provide evidence that insurers, hedge funds and asset managers tilt their portfolios towards higher risk bonds, consistent with ‘reaching for yield’ behaviour.     

The time‐varying performance of UK analyst recommendation revisions: Do market conditions matter?

This study examines the time‐varying performance of investment strategies following analyst recommendation revisions in the UK stock market, with specific emphasis on the impact of changing market conditions. We find a negative relationship between the recommendation performance and market conditions as measured in terms of past market return and market volatility. In particular, the upgrade (downgrade) portfolio generates significantly positive (negative) net abnormal returns in bad market conditions (e.g., the dot‐com bubble burst in 2000 and the credit crisis in 2007), but not in other periods of time. Moreover, our non‐temporal threshold regression analysis shows that the reported negative relationship disappears when market conditions become better, i.e., when the past market return (market volatility) is higher (lower) than a certain level, indicating the importance of taking non‐linearity into account in the long sample period as examined in this study. Our time‐series bootstrap simulations further confirm that the superior recommendation performance in bad market conditions is not due to random chance; analysts have certain skills in making valuable up/downward revisions in bad markets.