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1 / 205第11章 包含投资的实际跨期模型11.1 复习笔记一、典型消费者1．基本分析典型消费者在当期和未来的每一时期作出工作-闲暇决策，在当期作出消费-储蓄决策。
（1）典型消费者预算约束①基本假定a ．典型消费者在每一时期有h 单位的时间，并在每一时期都将该时间划分为工作时间和闲暇时间；b ．w 表示当期实际工资，w ′表示未来实际工资，r 表示实际利率，消费者当期和未来向政府缴纳的一次总付税，分别为T 和T ′；c ．把w 、w ′和r 视为给定，该典型消费者是价格接受者。
从消费者的角度看，税收也是给定的。
2 / 205②预算约束a ．当期预算约束当期，典型消费者挣得实际工资收入w （h －l ），从典型企业那里获得股息收入π，纳税T ，当期可支配收入是w （h －l ）＋π－T 。
当期可支配收入被划分为消费和储蓄，储蓄的表现形式是债券，获取的一时期实际利率为r 。
在这种情形下，消费者通过发行债券来借款。
于是，消费者的当期预算约束是：C ＋S P ＝w （h －l ）＋π－Tb ．未来预算约束未来，典型消费者获取的实际工资收入w ′（h －l ′），从典型企业那里获得股息收入π′，向政府纳税T ′，并获得当期储蓄的本息（1＋r ）S p 。
由于未来是最后时期，又由于假定消费者没有留下遗产，因此未来消费者的全部财富都用于消费，于是，消费者的未来预算约束是：C ′＝w′（h －l ′）＋π′－T ′＋（1＋r ）S pc ．一生预算约束把S p 代入当期预算约束，可以得到典型消费者的一生预算约束3 / 205该预算约束表明，消费的现值（等式左边）等于一生可支配收入的现值（等式右边）。
（2）典型消费者的最优决策典型消费者的问题是，选择未来消费C ′、当期消费C 、当期闲暇时间l 和未来闲暇时间l ′，使其境况尽可能改善，同时又满足一生预算约束。
消费者的最优决策的三个边际条件：①消费者在当期作出工作—闲暇决策，因此，当消费者实现最优时，有： MRS l ，c ＝w亦即消费者通过选择当期闲暇和消费，使闲暇对消费的边际替代率等于当期实际工资，就可以实现最优。
宏观经济学-课后思考题答案_史蒂芬威廉森011Chapter 11Market-Clearing Models of the Business CycleTeaching GoalsPhysics has so far failed to provide a unified theory to explain all physical phenomena. Economics is even further away from achieving such a goal. Keynesian models, while still popular among many policymakers, do not do a very good job of explaining the source and the mechanism by which the typical business cycle comes to pass. Although business cycles are remarkable similar, they are not identical, and they appear to have multiple causes.Equilibrium theorists have proposed a number of business cycle explanations that are based upon microeconomic principles and need not rely on markets failing to equilibrate. Interestingly, in contrastto the most basic of classical models, these models often admit a constructive role for macroeconomic policymaking.The real business cycle model emphasizes the point that shocks to total factor productivity are persistent, and that business cycles may represent the optimal response to such shocks. The segmentation markets model realizes that not everyone participates in financials markets and thus some agents are primarily effected by open market operations. The coordination failure model recognizes the possibility that strategic complementarities generate a kind of externality in production. While all of these considerations may, to a greater or less extent, be important factors in macroeconomic performance, a model that simultaneously considered all of these possibilitieswould be too unwieldy to provide coherent insights. Nevertheless, all of the possibilities of these models shed light on some causes and means of propagating business cycles.Classroom Discussion TopicsThe material in this chapter concludes the study of business cycle phenomena and macroeconomic stabilization policy. At this point it may be useful to revisit students’ original thoughts and prejudices about the proper role of government policy. With so many competing models, how would the students run monetary and fiscal policy if it were their job to do so? Does macroeconomics offer too many competing models and too many points of view? It can be helpful to point out that there is no consensus among macroeconomists on this issue. Should policy be used on a routine basis to fine-tune the economy? Should policymakers simply try to avoid significant fluctuations in the policy instruments? Should aggressive policy measures be employed against very serious shocks like the Great Depression?108 Williamson ? Macroeconomics, Third EditionOutlineI. The Real Business Cycle ModelA. The Workings of the Real Business Cycle Model1. Persistence of the Solow Residual2. Effects of a Persistent Change in Total Factor Productivity3. Qualitative and Quantitative Replication of the Business Cycle FactsB. Real Business Cycles and the Behavior of the Money Supply1. Cyclical Properties of the Money Supplya. Nominal Money Is Procyclicalb. Nominal Money Leads Real GDP2. Endogenous M oneya. Behavior of Bank Deposit Moneyb. Central Banks and Price-Level Stabilization3. Statistical Causality and True CausalityC. Implications of the Real Business Cycle Model for Government Policy1. Money Is Neutral2. Government Spending Based on Optimal Provision of Public Goods3. Other Policy Goalsa. The Friedman Ruleb. The Smoothing of Tax DistortionsD. Critique of the Real Business Cycle Model1. Measurement of Total Factor Productivity2. Labor Hoarding3. Real Business C ycle Theory and the “Volker Recession”II. The Segmented Markets ModelA. Limited Participation in Financial MarketsB. The Workings of the Model1. The Liquidity Effect2. Money Demand as a Function of the Expected Interest Rate3. Money Supply Surprises Are Not NeutralC. Implications1. Real Impact2. Money Injection Increases GDP and Components3. Average Labor Productivity Is Counterfactually Countercyclical4. Central Bank Can Be Welfare Improving: It Alleviates Cash ConstraintsD. Critique1. Relies on Central Bank Fooling Agents2. Relies on Firms Being Cash ConstraintChapter 11 Market-Clearing Models of the Business Cycle 109III. A Keynesian Coordination Failure ModelA. The Workings of the Model1. Coordination Failures2. Strategic Complementarities3.M ultiple Equilibria4. Increasing Returns to ScaleB. The Coordination Failure Model: An Example1. The Downward-Sloping Goods Supply Curve2. Multiple Intersections of Goods Supply and Goods Demand3. SunspotsC. Predictions of the Coordination Failure Model1. Properties of “Good” and “Bad” Equilibria2. The Coordination Failure Model and the Business Cycle FactsD. Policy Implications of the Coordination Failure Model1. Achieving a Single Equilibrium2. Does Policy Improve Performance?E. Critique of the Coordination Failure Model1. Evidence of Increasing Returns2. Unobservable ExpectationsTextbook Question SolutionsQuestions for Review1. Macroeconomic models should be based onmicroeconomic principles. Equilibrium models are the most productive vehicles for studying macroeconomic phenomena.2. Although business cycles are remarkably similar, they may have many causes. Alternative businesscycle models offer insights into one or more key features of the economy and some aspects of the e conomy’s response to macroeconomic shocks. Policymakers need as much insight as possible to guide their actions.3. In the real business cycle model, persistent shocks to total factor productivity cause output tofluctuate.4. Although changes in the money supply change nominal prices in the real business cycle, they changeneither perceived nor actual relative prices. There is therefore no reason for firms or consumers to change their behavior.5. In the real business cycle model, changes in the money supply may be endogenous. In particular,when output increases due to a total factor productivity shock, the banking system is likely toincrease the quantity of deposit money, and the Fed may increase the monetary base in order tostabilize the aggregate price level.6. In the real business cycle model, firms and consumers in the economy make optimal responses tochanges in total factor productivity. Therefore, policy cannot improve matters, and may actually make matters worse.110 Williamson ? Macroeconomics, Third Edition7. The real business cycle provides a good explanation of the business cycle facts, both qualitatively andquantitatively.8. There are some phenomena that the real business cycle model cannot adequately explain. As oneexample, there is good evidence that the U.S. recession of 1981–82 was due to a monetary policy shock. The real business cycle model has no explanation of monetary nonneutrality.9. It is because it affects agents after they have made their money choices and, in this model, allows thefirm to adjust its activities that are cash constrained.10. Only if it does that intelligently. Purely random policy would be detrimental, as it would throw agentsoff their plans. But if it helps them as they face shocks, for example by alleviating cash constraints, then it is good stabilization policy. The central bank, however, needs to have very good information and needs to act quickly.11. Remarkably well, except for the countercyclical average labor productivity.12. Parties are more fun when a lot of people attend. If everyone believes that others will attend,everyone goes to the party and has a good time. However, if most people think that others are not going, they will also choose not to go, few people will show up and the party will be much lesssuccessful. The coordination failure arises because people may not be able to jointly decide whether they will attend.13. In the coordination failure model, business cycles may occur if consumers and firms are alternativelyoptimistic and pessimistic. Aggregate-level increasing returns to scale then set in to amplify the effects of such changes in attitude.14. The coordination failure model is an equilibrium model. In the absence of any other changes inbehavior, changes in the money supply change the aggregate price level, but they do not change relative prices. Therefore, consumers and firms continue to make the same choices.15. The coordination failure model does a very good job in fitting the facts of the typical business cycle.16. The choice of which model is better depends on how we interpret some of the more detailedevidence. However, both models may shed some light on some features of different business cycle events, and both models may offer some insights that may be useful for policymakers.Problems1. The response to a temporary change in government spending in the real business cycle model is thesame as the response to such a disturbance in the monetary intertemporal model, as the two models are equivalent. Government spending shocks in this model wrongly predict that consumption,investment, and the real wage are countercyclical. In response to a temporary increase in government spending, output increases and the real interest rate increases. Because the net effect on moneydemand is ambiguous, the effect on the price level is also ambiguous. Therefore, there can be no contradiction of model’s predictions on the cyclical behavior of the price level.Chapter 11 Market-Clearing Models of the Business Cycle 111 2. We already know that persistent increases in total factorproductivity are consistent with all of thebusiness cycle facts. As developed in the answer to problem 4, above, we noted that temporaryincreases in government spending were not consistent with several of the business cycle facts. If both disturbances are combined, the ability to fit the facts depends on which of the parts of the disturbance are stronger. In particular, if the increase in government spending produces a small increase in total factor productivity, then this type of disturbance will not fit the facts very well. For this type ofdisturbance to fit the business cycle facts, a small increase in government spending would need to generate a large increase in total factor productivity.3. Business optimism about future total factor productivity.(a) First consider the fundamental effects of the increase in expected future total factor productivity.Such a disturbance shifts the aggregate demand curve to the right. In the coordination failuremodel, this results in an increase in output and employment in the good equilibrium and adecrease in output and employment in the bad equilibrium. The increased optimism might alsomove the economy from the original bad equilibrium to the new good equilibrium.(b) Let us focus on the effects of changes in future total factor productivity on the good equilibrium.This disturbance shifts the aggregate demand curve to the right. The good equilibrium is at higher levels of output and employment, and a lower real interest rate. In the labor market, the reduction in the real interest rate also increases the real wagerate. The decrease in the real interest rateincreases consumption spending. The increase in the real interest rate likely mitigates, but doesnot reverse, the direction of the effect of the disturbance on investment. All of these effects areconsistent with the business cycle facts. Finally, the increase in output and the reduction in thereal interest rate both work to increase money demand. The price level therefore decreases, which is also consistent with the business cycle facts.(c) The increased optimism decreases the price level in the good equilibrium. Therefore, themonetary authority should increase the money supply when firms become more optimistic andreduce the money supply when firms become more pessimistic. Note that if the money supply isa sunspot variable, there may be a difficulty with reducing the money supply when firms becomemore pessimistic. This policy response is therefore consistent with the nominal money supplybeing procyclical. Such a change in the money supply may also shift the economy from the good equilibrium to the bad equilibrium, and this factor obviously greatly complicates the analysis.4. Announced policies in the segmented markets model.(a) In this case, the expected real interest rate r e is unaffected, despite the announcement, and moneysupply M s is reduced. This is equivalent to an unexpected decrease of the money supply, and we have the exact opposite situation from what is described in Figure 11.5 of the textbook.Thus, the interest rate and the price level will increase; employment, output, consumption, and investment all decrease.(b) As this announcement is believed, all agents will be able to react to it and there is no marketsegmentation. We are thus back to the monetary model of Chapter 10. Real aggregates areunaffected, only the price level decreases.(c) The price level changes more in the second situation, as there is no real impact that wouldcounterbalance it. Now to make its policy announcements more credible, the central bank would need to show consistently that it is acting like it said it would. This can, for example, be attained by sticking to a well-publicized rule.112 Williamson ? Macroeconomics, Third Edition5. We want to compare here a positive money supply shock as it affects economies a and b that areinitially at steady state. The shock is larger in economy a. The figures below build on Figure 11.5 from the textbook, the only difference being the amplitude of the shocks. The steady states are the same for both countries, with one exception: money demand is lower in country a due to the higher uncertainty about prices. Indeed, households do not like variations, thus all agents will use more banking services to avoid the larger consequences from price variations. The consequence is that all aggregates fluctuate more in country a. While the price level is initially higher in country a, it may fall below the one in the other country, depending on the difference in money demands between the two countries. But the price level fluctuates more for sure in country a. The figures belowillustrate this.Chapter 11 Market-Clearing Models of the Business Cycle 1136. If the money supply were the only variable that shifts the economy between the bad and good states,the monetary authority would need to increase the money supply only if the economy starts out in the bad state. However, once the good state is reached, there is no further need to make any changes in the money supply. Both models are therefore consistent with a predictable money supply as the best way to make consumers better off.On the other hand, if there was a disturbance that shifted the economy into the bad state, it would be optimal for the monetary authority to increase the money supply when output falls. In the money surprise model, changes in the money supply in response to disturbances can only make consumers worse off.7. The reduction in the demand for leisure implies a rightward shift in labor supply. This shift in laborsupply implies an equilibrium in the labor market with less employment and a decreased real wage.The aggregate supply curve therefore shifts to the left. The increase in the demand for consumption goods shifts the aggregate demand curve to the right. Therefore, in the good state, output increases and the real interest rate decreases. In the bad state, output decreases and the real interest rate increases.114 Williamson ? Macroeconomics, Third Edition8. The permanent increase in government spending does not affect the aggregate demand curve, becausethe increase in government spending generates an approximately equal decrease in consumption. The implied increase in taxes shifts the labor supply curve to the right. In the coordination failure model this produces a leftward shift in aggregate supply. Recall that the labor demand curve is upward sloping and steeper than the labor supply curve. A leftward shift in aggregate supply is depicted in the figure below.In the “good” equilibrium, output increases and the real interest rate decreases. That output increases requires that employment increase. The increase in employment moves the economy along the labor demand curve, so that the real wage rate must also increase. Finally, the increase in output combined with the decrease in the real interest rate implies that money demand shifts to the right, and so the price level decreases.In the “bad” equilibrium, output decreases and the real interest rate increases. That output decreases requires that employment decrease. The decrease in employment moves theeconomy along the labor demand curve, so that the real wage rate must also decrease. Finally, the decrease in output combined with the decrease in the real interest rate implies that money demand shifts to the left, and so the price level increases.Chapter 11 Market-Clearing Models of the Business Cycle 115 9. The effects of the decrease in the capital stock depend on the specific model we are working with.The effect of the decrease in capital in the real business cycle is depicted in the figure below.116 Williamson ? Macroeconomics, Third EditionThe real interest rate unambiguously increases. The diagramdepicts a case in which real outputdecreases. In this case, the demand for money unambiguously decreases, and so a decrease in the money supply is required to maintain price stability. If, on the other hand, the increase in investment demand is strong enough, then the aggregate demand curve may shift to the right by more than the shift to the left in aggregate supply. In this case, real output increases. If real output increases enough, then the demand for money may increase. This case would require an increase in the money supply.In the coordination failure model, the situation is more complex. The decrease in the capital stock shifts the aggregate production function downward, as in the figure below. The new aggregateproduction function is flatter, so that the aggregate labor demand curve shifts downward. Employment would therefore increase. The increase in employment coupled with the decrease in the capital stock, may either increase or decrease the level of output. If, as depicted in the figure below, output on net decreases, then the aggregate supply curve shifts to the left.Chapter 11 Market-Clearing Models of the Business Cycle 117 The decrease in the capital stock also shifts the aggregate demand curve to the right. If the aggregate supply curve shiftsto the left, then the situation is as depicted in the figure below. In the bad equilibrium, output decreases and the real interest rate increases. Money demand would therefore decrease, and the money supply would need to decrease to maintain price stability. In the good equilibrium, output increases and the real interest rate decreases. Money demand would increase, and so the money supply would need to increase to maintain price stability.。
一、思考题 2.什么是总供给函数?说明总供给曲线的通常形状。
3.什么是总需求函数?怎么推导出总需求曲线?4.试比较"古典"AS —AD 模型和修正的凯恩斯的AS —AD 模型。
5.用图形说明短期均衡的三种状态。
(萧条、高涨和滞胀)6.说明完全凯恩斯模型的方程及其图像。
7.简述凯恩斯效应与庇古效应的含义及其比较。
8.叙述理性预期ES —AD 模型及政策含义。
9.评析宏观经济基本理论的演变。
二、计题1.有一古典的 AS-AD 模型，总供给函数 Y=Y f =1000， 求：（ 1）均衡价格水平；（ 2）如价格不变，总需求函数变为 P=1000-0.4Y 时，经济会怎样？（ 3）如总需求函数为 P=1000-0.4Y ，价格可变动时，均衡价格变动多少？2.假定某经济社会的短期生产函数为 Y=14N-0.04N 2，劳动力需求为 N d =175-12.5（W/P ），劳动力供给函数 N s =70+5(W/P)，求（ 1）当 P=1和 P=1.25时，劳动力市场均衡的就业量和名义工资率分别是多 少？（ 2）当 P=1和 P=1.25时，短期产出水平是多少？3.有一封闭经济，假定存在以下经济关系：在商品市场上，C=800+0.8Y D ， T=t y =0.25y ，I=200-50r ，G=200。
在货币市场上，M d /P ＝0.4y-100r ，Ms=900。
试 求：（1）总需求函数；（ 2）价格水平 P=1时的收入和利率；（ 3）如总供给函数为 Y=2350+400P ，求 AS=AD 时的收入和价格水平。
参考答案：一、思考题1.答：在凯恩斯模型基础上，引入价格变量，和供给因素(即劳动市场)，研 究产量(或国民收入)和价格水平的决定问题。
经济学家对总供给曲线形状的观点 不一致，因此存在许多不同形状和解释的总供给——总需求模型。
2.答：总供给函数中总产量与价格水平的对应关系可表示为总供给曲线。
黄亚钧《宏观经济学》第3版课后习题第十一章宏观经济政策和理论1．为什么一些经济学家认为，被动性政策反而有助于经济的稳定？答：被动性政策有助于经济稳定的原因在于：（1）政策效果滞后。
政府在试图稳定宏观经济运行时，其采取行动的时机以及这些政策行动的最终生效，往往会滞后于实际经济的运行，因而常常带来适得其反的效果。
（2）宏观经济的不确定性。
由于时滞的存在，宏观经济政策要到实施后很久才会起效，这就要求政策制定者能精确地预测将来的经济情况。
但是，经济的发展趋势往往是难以预计的。
（3）卢卡斯批判。
卢卡斯认为，人们的预期会对经济政策的变动作出反应，并对经济政策形成反作用，从而抵消经济政策的效果。
2．卢卡斯批判的核心内容是什么？它对宏观经济政策之争产生了什么影响？答：从凯恩斯学派看来，总供给曲线是僵化的，没有生命力；而在卢卡斯眼中，总供给曲线是可变的，富有生命力的，它会对政府的宏观政策做出反应，政策制定者要了解和重视这种反应。
这就是“卢卡斯批判”的重点所在。
凭借对凯恩斯主义稳定性经济政策的批判，卢卡斯为新古典主义经济学提供了有力的理论支持。
3．什么是政策的“时间不一致性”，你能举出中国经济生活中的实例来说明这一点吗？答：政策制定者在特定时点上做出的相机抉择尽管在当时可能是理性选择，但从长期来看却不能取得良好的政策效果，这就是政策的“时间不一致性”。
宏观经济政策的作用过程实质上是政府与公众的博弈过程，政府开始时宣布一个规则，公众根据这一规则形成自己的预期；但一旦公众预期形成，政府就可能在这一预期下重新决策，从而违背自己开始时宣布的规则。
举例：中国在2009年大规模的信贷投放对经济率先走出金融危机起到十分重要的作用，但由此引发了未来发生通货膨胀的隐患，而收缩信贷却又担心经济是否会二次探底。
上述货币政策的困境在很大程度上表现为货币政策的时间不一致性问题。
4．为什么经济学家认为宏观经济政策应该是管理预期而不是调控经济？答：如果政策制定者采取的政策是时间不一致的，尽管有可能减少短期的社会损失，但由于政策制定者没有兑现承诺，从长期来看会付出更大的代价。
第11章市场出清的经济周期模型11.1 复习笔记一、经济周期理论概述1．经济周期理论的发展进程（1）凯恩斯的经济周期模型货币在短期不是中性的，这种非中性是由工资和价格的短期刚性引起的。
在凯恩斯模型中，价格和工资刚性以及由此造成的所有市场可能无法在每一时点上出清，是经济冲击造成总产出波动的形成机制的关键所在。
价格和工资缓慢向出清的市场变动的事实，意味着货币政策和财政政策在应对总冲击时可以发挥稳定经济的作用。
（2）货币主义的经济周期模型货币主义者往往认为，货币政策是比财政政策更有效的稳定工具，但他们对政府政策微调经济的能力持怀疑态度。
一些货币主义者认为，在短期，政策可能是有效的，但非常短。
（3）理性预期学派的经济周期模型理性预期革命提出的两大原则是：①宏观经济学模型应建立在微观经济学原理的基础上，即这些模型应以对消费者和企业的偏好、禀赋、技术和最优行为的描述为后盾；②均衡模型是研究宏观经济现象的最有成效的工具。
2．分析不同经济周期理论的必要性（1）财政政策和货币政策的决策者能够通过经济周期理论，了解左右经济的宏观经济冲击是什么，它对未来总体经济活动有什么影响。
（2）每一种经济周期模型都能确定经济的一个或几个特征及经济对宏观经济冲击作出反应的一些方面。
如果将所有这些特征纳入一个模型中，将无助于认识经济周期表现的基本规律和政府政策。
二、真实经济周期模型真实经济周期模型由芬恩·基德兰德和爱德华·普雷斯科特于20世纪80年代初首创。
1．全要素生产率持久提高的均衡效应假定货币跨期模型中的全要素生产率是持久提高，即z和z＇分别提高。
（1）全要素生产率z提高的影响①当期z提高会增加每一数量劳动投入的边际劳动产出，劳动需求曲线右移，从而导致产出供给曲线右移。
如图11-1所示。
图11-1 真实经济周期模型中全要素生产率持久提高的影响②预期未来全要素生产率z＇提高的影响：a ．投资品需求会增加，因为典型企业预期未来边际资本产出会增加；b ．典型消费者预期较高的未来全要素生产率会带来较高的未来收入，因此一生财富增加，消费品需求增加。
