Patterns of poverty among elderly Americans: a latent class Markov model

This article studies poverty persistence and the role of social security programmes on poverty among elderly in the US. We use a Latent Markov model to disentangle unobserved heterogeneity and state dependence. Because of its dynamic nature, unobserved heterogeneity is modelled to vary over time. This allows to capture different latent states of poverty that change over time. Result indicates the existence of three unobserved types evolving over time according to their propensity to be poor. Moreover, a strong persistence in poverty especially for women, individuals living alone and ethnic minorities is found. Finally, the estimates indicate that giving social assistance tends to reduce poverty.     

The long-run reversal in the long run: Insights from two centuries of international equity returns

We perform the most comprehensive test of long-term reversal in national equity indices ever done. Having examined data from 71 countries for the years 1830 through 2019, we demonstrate a strong reversal pattern: the past long-term return negatively predicts future performance. The phenomenon is not subsumed by other established cross-sectional return patterns, including the value effect. The long-term reversal is robust to many considerations but highly unstable through time. Finally, our findings support the overreaction explanation of this anomaly.     

Assessing the contribution of artisanal fisheries to food security: A bio-economic modeling approach

Artisanal fisheries are an important food source in many developing regions. Quantitative bio-economic models are needed that comprehensively assess artisanal fisheries’ contribution to food security. Our model combines standard resource economics theory with the literature on food systems. It explains impacts of environmental variations and market development on output, prices and ultimately food security. The application to the Senegalese purse-seine fishery reveals that total sector rents account for 2% of per capita yearly food expenditures for the coastal inhabitants. We examine the relative importance of main drivers and the vulnerability of different regions. Market development plays a crucial role: The resource is of far greater relevance for remote regions.     

科技企业孵化器何以激活区域创新——风险投资与孵化基金的中介作用

完善创新生态系统、提升区域创新能力是我国科技企业孵化器建设的重要目标。基于2013-2018年中国（内地）30个省份面板数据，采用面板数据模型实证检验科技企业孵化器是否促进了区域创新能力提升，并基于中介效应模型探讨风险投资和孵化基金在其中的间接作用。结果发现：①科技企业孵化器建设显著提升了区域创新水平，但主要增加的是实用新型和外观设计专利申请授权数总量，对发明专利申请授权数并没有显著促进作用。上述结果在剔除直辖市样本、采用随机效应模型及空间计量模型的稳健性检验后依然成立；②通过中介效应模型检验发现，区域风险投资和孵化基金集聚效应是科技企业孵化器影响区域创新水平的主要机制；③科技企业孵化器对区域创新的影响在不同区域间差异较大，在东部地区的创新激励效应更加显著，而且政策工具强度对科技企业孵化器与区域创新水平的关系具有正向调节作用。     

Estimating yield curves of the U.S. Treasury securities: An interpolation approach

Following the approach of interpolation, this paper proposes the multiple exponential decay model to fit yield curves for both the U.S. TIPS market and the conventional Treasury security market. Several estimation methods, including the unconstrained/constrained nonlinear minimization, quadratic programming, and the iterative linear least squares, are applied to estimate the unknown parameters according to different curve‐fitting purposes. Comparisons between the proposed model and the alternatives show that the multiple exponential decay successfully (1) adapts to a variety of shapes associated with yield curves, (2) (partially) keeps in line with the economic interpretations of Nelson–Siegel summarized by Diebold and Li ( 2006 ), and (3) dominates the competing models in curve‐fitting performance measured by mean fitted‐price errors over the sample period. In addition, the exact specification of a nonparametric interpolation model is pinned down by applying three statistical tools, which enable us to jointly take into account validity, optimality, and parsimoniousness of the proposed model.     

Optimal social security tax with myopic agents

Myopic agents lack the foresight to save for their own old age. It is generally believed that correcting myopia is a rationale for a pay-as-you-go (PAYG) pension system. This view has been supported by existing literature showing that the optimal PAYG social security tax should increase when people are more myopic. In this paper we obtain new results opposed to the traditional view. By establishing a very standard general equilibrium OLG model with myopic agents and endogenized marginal product of capital, we show that the optimal social security tax should be lower when people are more myopic. Our numerical analysis also shows that the welfare cost of the social security tax increases with people's degree of myopia. These results suggest that correcting myopia is not a clear rationale for the PAYG social security.     

粮食安全与农业结构调整水平的协整分析*——以广东省为例

[目的]实现我国粮食安全与农业结构调整之间(即粮食增产和农民增收)关系的协调,较长时间以来是学界、政界关注的重要议题,但定量分析两者之间内在依存关系的研究一直欠缺。[方法]文章采用协整分析及Granger因果关系检验方法,以广东为例,对我国粮食安全(用粮食总产量来衡量)与农业结构调整水平之间的协整性及因果关系进行了研究。[结果]广东粮食总产量与反映农业结构调整水平的3个指标之间均存在长期均衡关系,且农作物播种面积中粮食作物面积对广东粮食总产量影响最大,每下降1%,粮食总产量下降0. 659 548%。短期内,反映农业结构调整水平的3个指标对广东粮食总产量的影响均存在波动,但由短期偏离拉向长期均衡的牵动作用均较弱。Granger因果关系检验表明农业在国民经济中的比重、农作物播种面积中粮食作物面积早期对广东粮食总产量产生单向影响,但影响程度相对较弱。[结论]提出应从农业结构调整以外的因素着手提高我国粮食安全水平,并通过调整农业区域结构去缓解我国粮食供求市场的结构性矛盾。     

Matching food security and malnutrition indicators: evidence from Southeast Asia

This article aims to understand the relation between household food security and individual undernutrition. The multitude of indicators available raises the question which aspects of food security are captured by the respective indicator. In our analysis, we first assess the relation between the dimensions of food security and households’ socioeconomic characteristics. Second, we examine whether household indicators detect undernutrition in children. Finally, we investigate the role of individual‐specific characteristics for child undernutrition. The analysis is based on a novel data set of 1,200 rural households from Cambodia and Lao PDR, which combines household‐ and individual‐level data. We capture household food security by three indicators including a dietary diversity score, a consumption behavior measure, and an experiential measure. Individual nutrition status is measured via anthropometric indicators. Our results show that different household‐level indicators capture fundamentally different aspects of food security. Moreover, household food security fails to explain stunting for children under five. Dietary diversity indicators, however, explain underweight in children to a small extent. We call for more research on intrahousehold allocation of food and stress the implications of our research for the design and targeting of food and nutrition support programs.     

社保基金持股与企业盈余质量:A股上市公司的证据

本文利用中国A股上市公司2006-2015年的数据,研究社保基金持股对上市公司盈余质量的影响。我们用上市公司财务重述作为测度盈余质量的指标,发现社保基金持股能够显著降低企业发布财务重述的概率,这表明社保基金对上市公司盈余质量的提高具有促进作用。并且,社保基金的这一治理作用在国有企业、内部治理水平较差以及市场化程度较低地区的上市公司中更加显著。通过双重差分模型和安慰剂检验等方法弱化了内生性问题之后,以上结论依然成立,说明社保基金持股和盈余质量提升之间存在因果关系,我们称之为社保基金的公司治理作用。进一步研究发现,社保基金可以通过抑制控股股东资金占用、增加机构调研次数等途径提升被持股公司的盈余质量。本文有助于认识和评估社保基金持股对于上市公司的监督与治理作用。     

国家安全视角下的生物资源安全与保护制度研究

2014年习近平总书记提出了“总体国家安全观”理念,这是我国社会主义理论制度的又一伟大创新。本文从本次新冠疫情对于国家综合安全利益的影响出发,结合疫情对国家安全要素的扩张以及对国家安全利益的威胁等实际情况,探寻本次疫情暴露出的国家安全制度中存在的问题,以期完善我国以生物资源和公共卫生安全为代表的公共安全管理制度和疫情防控制度。