人口结构变迁、福利制度错配与主权债务适度规模

老龄化和高公共福利支出是影响希腊、意大利等欧洲国家债务持续性的重要因素。医疗保障与养老金支出作为刚性财政支出无法形成税收，债务融资成为政府弥补财政缺口的主要手段，同时脱离了经济发展约束的福利制度进一步恶化了政府的财政状况。基于三期世代交叠模型，理论研究发现人口老龄化、公共福利支出的增加将扩大政府债务规模。实证研究结果显示，老年抚养比、养老金替代率等指标对债务规模影响显著。此外，债务负担率高于《马斯特里赫特条约》的欧洲国家，人口与福利指标对负债的边际影响更为强烈，这种差异来自于不同阶段的老龄化成本和人口结构变化速度，印证了主权债务规模应适度。

Demographic Transition,Welfare System Mismatch and Moderate Scale of Sovereign Debt

As substantial demographic changes unfold at a globe level,the world population is getting older .Theoretically all European countries should have tax financed education,health care and public pension systems,because there is a strong age component with respect to when the representative benefits from and contributes to public finances .However,the government may run deficits to smooth adjustments across time and generations given a policy package such as high welfare standards . Therefore,ageing and high public welfare expenditure are important factors of debt sustainability in Greece,Italy and other European countries .This paper proposes that bond issue is gradually turning into the primary means for governments to plug their fiscal shortfalls since rigid fiscal unproductive expenditure could not generate tax revenue .Besides,the government financial situation gets even worse because of welfare system mismatch which leads to a full-blown debt crisis eventually . Based on the three-period OLG model,we discuss the net contributions of representatives of different stages in the public sector,and integrate demography and welfare expenditure into the analysis framework of sovereign debt according to the fiscal gap model .The proposition we put forward is that ageing and the rise of social security expenditure would lead to the increase of government debt ratio .In this paper,empirical research was conducted in 28 European countries from 2003 to 2012 .We constructed variables,including the proportion of the population aged 65 or above,old age dependency ratio,life expectancy to capture the demographic transition;relative median income ratio,aggregate replacement ratio,expenditure on pensions,social protection,health care,and education to capture welfare system arrangement;and adopted the inflation rate,average yields of national debt,birth rate,economic growth rate,fiscal deficits,tax revenue as control variables .Considering heteroscedasticity of panel data,we made use of the fixed effects model with clustering robust standard deviation,and applied first-lagged variables to control the possible endogeneity . The empirical results show that :(1) Consistent with the theory,aggregate replacement ratio,expenditure on social protection,and old age dependency ratio have positive influence on scale of debt .(2) Aggregate replacement ratio is less significant when debt ratio is higher than 60%,however it is very significant otherwise .This is because aggregate replacement rate maintains stable and does not change with the increase of debt ratio when debt ratio is high .In other words,governments don't have the ability to continuously improve welfare because of fiscal dilemma which leads to the stagnation of treatment for retirees after achieving a certain level .(3) At a high debt level,expenditure on social protection and old age dependency ratio have more significant marginal effect which coming from the expansion of the aging population .In short,the scale of debt will still grow geometrically under the present welfare system . This paper provides a new theoretical framework about sovereign debt from a demographic perspective,confirms the significant relationship among ageing,public welfare system and government debt in theory and practice,and indicates that controlling the speed and cost of population aging is an effective means of maintaining appropriate scale of sovereign debt .