清华大学：经济学原理：Ch_03_2

1 物品市场 The Goods Market 第3章 Chapter 3 短期 The Short Run 在短期内，需求决定产出。许多 因素影响需求，包括消费者信心 、财政与货币政策等。 In the short run, demand determines output. Many factors affect demand, from consumer confidence to fiscal and monetary Policy. 物品市场 The Goods Market 当经济学家考虑经济活动的逐年变化时，他们 关注生产、收入与需求之间的相互影响。 When economists think about year-to-year movements in economic activity, they focus on the interaction between production, income, and demand. 物品市场 The Goods Market ?对物品需求的变化导致生产的变化。 Changes in the demand for goods lead to changes in the production. ?生产的变化导致收入的变化。 Changes in production lead to changes in income. ?收入的变化导致对物品需求的变化。 And changes in income lead to changes in the demand for goods. GDP的构成 The Composition of GDP ?企业购买机器的决定因素不同于消费者购买食物、联 邦政府购买新战斗机的决定因素。 Purchases of machines by firms depend on different factors than do purchases of food by consumers, or purchases of new combat airplanes by the federal government. ?如果我们要考虑什么决定对物品的需求，有必要从所 生产的不同物品以及对这些不同物品的买者的角度来 分解总产出（GDP）。 If we are to think about what determines the demand for goods, it makes sense to decompose aggregate production (GDP) from the point of view of the different goods being produced, and the different buyers for these goods. GDP的构成 The Composition of GDP ?消费Consumption (C) ?投资Investment (I) ?政府支出Government Spending (G) ?净出口Net Exports (X – Q) ?库存投资Inventory Investment (I s ) 2 消费 Consumption ?消费代表消费者购买的物品与服务。 Consumption (C) represent goods and services purchased by consumers. ?食物，机票，度假，新车，…… Food, airline tickets, vacations, new cars,… 投资 Investment ?投资有时被称作固定投资，以区别于库存投资 Investment (I) is sometimes called fixed investment to distinguish it from inventory investment. ?投资是非居民投资和居民投资之和。前者指企 业对于新工厂与及其的购买（例如涡轮机、计 算机），后者指人们对于新房屋或公寓的购买 Investment is the sum of nonresidential investment, the purchase by firm of new plants or new machines (from turbine to computers), and residential investment, the purchase by people of new houses or apartments. 投资 Investment ?企业购买机器或者厂房是为了能够在将 来生产更多的产出。 Firms buy machines or plants to be able to product more output in the future. ?人们购买房屋或者公寓是为了未来得到 住房服务。 People buy houses or apartments to get housing services in the future. 政府支出 Government Spending ?政府支出代表联邦、州和地方政府购买的物品和服务 Government Spending, (G), represents the purchase of goods and services by the federal, state, and local governments. ?物品包括飞机到办公设备。 The goods range from airplanes to office equipment. ?服务包括政府雇员提供的服务。 The services include services provided by government employees. ?实际上，国民收入帐户认为是政府购买了政府雇员提供的服务— —然后免费提供给公众。 In effect, the national income accounts treat the government as buying the services provided by government employee – and then providing these services to the public, free of charge. 政府支出 Government Spending ? G不包括政府转移支付，例如医疗保险或者社 会保险，也不包括政府支付的债务利息。 G does not include government transfers, such as Medicare or Social Security, nor interest payments on the government debt. ?虽然这些属于政府的开支，但他们不是对于物 品和服务的购买。 Although these are clearly government expenditures, they are not purchases of goods and services. 净出口 Net Exports ?进口代表美国消费者、企业或者政府购买的外 国的物品和服务。Imports (Q) represents the purchases of foreign goods and services by U.S. consumers, U.S. firms, and the U.S. government. ?出口代表外国购买的美国的物品和服务。 Exports (X) represents the purchases of U.S. goods and services by foreigners. ?出口和进口之差被称作净出口，或贸易余额。 The difference between exports and imports, (X – Q), is called net exports, or the trade balance. 3 净出口 Net Exports ?如果出口大于进口，一国就有了贸易盈 余。 If exports exceed imports, a country is said to run a trade surplus. ?如果出口小于进口，该国就有了贸易赤 字。 If exports are less than imports, the country is said to run a trade deficit. 库存投资 Inventory Investment ?一些物品是某年生产的，但不在该年出售，而是来年 出售。一些物品是某年出售的，但却是往年生产的。 Some of the goods produced in a given year are not sold in that year, but sold in later year. Some of the goods sold in a given year may have been produced in an earlier year. ?某年的物品生产量与出售量之差被称作库存投资。 The difference between goods produced and goods sold in a given year – equivalently, between production and sales – is called inventory investment and is denoted I s . 库存投资 Inventory Investment ?如果生产大于销售，企业积累库存。库存投资 是正的。 If produce exceeds sales, firm accumulate inventories. Inventory investment is positive. ?如果生产小于销售，企业减少库存。库存投资 为负。 If produce is less than sales, firms decrease inventories. Inventory investment is negative. 美国GDP的构成 The Composition of U.S. GDP, 1998 Billions of Dollars Percent of GDP GDP (Y) 8509 100 Consumption (C) 5806 68 Investment (I) 1308 15 Nonresidential 939 11 Residential 369 4 Government Spending (G) 1488 18 Net Exports -154 -2 Exports (X) 958 11 Imports (Q) -1112 -13 Inventory Investment (I S )61 1 物品的需求 The Demand for Goods 对物品的总需求可以写成： The Total demand for goods (Z) can be written as: Z ≡ C + I + G + X - Q 基本假设 Basic Assumptions ?假设1：所有企业生产相同的物品，它既可以为消费者 用来消费，也可以被企业用来投资，或者为政府所用 Assumption 1: All firms produce the same good, which can be used by consumers for consumption, by firms for investment, or by the government. ?有了这一简化，我们只需要关注一个市场——“该”物 品的市场——考虑在这个市场中供给和需求的决定因 素。 With this simplification, we need to look at only one market – the market for “the” good – and think about what determines supply and demand in that market. 4 基本假设 Basic Assumptions ?假设2：在某一给定价格下，企业愿意供给任 何数量的物品。 Assumption 2: Firms are willing to supply any amount of the good at a given price. ?换句话说，物品的供给在价格P上是完全富于 弹性。 In other words, the supply of goods is completely elastic at price P. ?这一假设允许我们集中关注需求在决定产出上 的作用。 This assumption will allow us to focus on the role of demand in the determination of output. 基本假设 Basic Assumptions ?这一假设只在短期内成立。 This assumption in valid only in the short run. ?当我们转而研究中期时，我们需要放弃 这一假设。 When we move to the study of the medium run, we shall need to give up this assumption. 基本假设 Basic Assumptions ?假设3：经济是封闭的，即它不与世界的其他 部分进行贸易。 Assumption 3: The economy is closed, that it does no trade with the rest of the world. ?出口与进口都等于零。 Both exports and imports are equal to zero. X = Q = 0 ? Z ≡ C + I + G 消费的决定因素 The Determination of Consumption ?消费的主要决定因素显然是收入，更准确的说，是可 支配收入，即消费者在得到来自政府的转移支付并支 付税收后剩下的收入。 The main determinant of consumption (C) is surely income, or more precisely disposable income (Y D ), the income that remains once consumers have received transfers from the government and paid their taxes. C = C(Y D ) (+) ?函数C(Y D ) 被称作消费函数。 The function C(Y D ) is called the consumption function. 消费的决定因素 The Determination of Consumption ?经济学家把这样的方程叫做行为方程，因为这 一方程反映了某些方面的行为——这里是消费 者的行为。 Economists call such an equation a behavioral equation, to indicate that the equation reflect some aspect of behavior – in this case, the behavior of consumers. 消费的决定因素 The Determination of Consumption ?假定消费函数是线性的。 Assume that the consumption function is a linear relation. C = c 0 + c 1 Y D ?参数c 1 被称作（边际）消费倾向。0<c 1 <1。 The parameter c 1 is called the (marginal ) propensity to consume. 0<c 1 <1. ?参数c 0 表示人们当年的可支配收入等于零时的消费。 The parameter c 0 is what people would consume if their disposable income in the current year were equal to zero. c 0 >0. ?如果收入为零，人们通过动用储蓄——卖掉现有资产来保持 正的消费。 People have positive consumption if their income is zero by dissaving –by selling some of their assets, or by borrowing. 5 消费的决定因素 The Determination of Consumption Disposable Income,Y D Consu m pt ion , c Consumption function C = c 0 + C 1 Y D Slope = c 1 c 0 消费的决定因素 The Determination of Consumption ?可支配收入等于： Disposable income is given by Y D ≡ Y – T 这里Y是收入，T是税收减去消费者得到的政府转 移支付。 where Y is income and T is taxes paid minus government transfers received by consumers. ?这是一个恒等式。This equation is an identity. C = c 0 + c 1 (Y – T) 为什么价格不再是 决定消费的主要因素？ ?在微观经济学中，消费者对某一物品的 需求取决于它的相对价格(relative price) ，即它相对于其他物品的价格。 ?在宏观经济学中，所有物品（看成一种 物品）的消费需求与整体物价水平(price level)的关系，最终体现在物价水平对消 费者的购买力——实际收入(Real income) ——的影响当中。 投资的决定因素 The Determination of Investment ?我们将投资视为给定，写成： We shall take investment as given, and write I =?I 投资的决定因素 The Determination of Investment ?模型有两类变量： Models have two types of variables. ?一些变量依赖于模型中的其他变量，因而在模型内 得到解释——内生变量。 Some variables depend on other variables in the model, and are therefore explained within the model – Endogenous variables. ?例如，消费E.g., consumption (C) ?另外一些变量不在模型内进行解释而是给定的—— 外生变量。Other variables are not explained within the model but are instead taken as given – Exogenous variables. ?例如，投资E.g., investment (I) 政府支出的决定因素 The Determination of Government Spending ?我们将政府支出，连同税收一起，视作 外生的。 We shall take government spending (G) , together with taxes(T), as exogenous. 6 为什么将G和T视作外生的？ Why we take G and T as exogenous? ?政府的行为不如消费者或者企业规则。因此没有象描 述消费者那样的可靠法则来描述G或者T。 Government do not behave with the same regularity as consumers or firms, so there is no reliable rule we could write for G or T corresponding to the rule we wrote for consumption. ?宏观经济学家的一个任务是向政府提出关于支出和税 收（财政政策）的建议。 One of the tasks of macroeconomists is to advise government on spending and tax decisions – fiscal policy. 需求的决定 The Determination of Demand ?对物品的需求是消费、投资和政府支出之和。 The demand for goods (Z) is the sum of consumption (C), investment (I), and government spending (G): Z ≡ C + I + G ?对物品的需求取决于收入、税收、投资与政府 支出。 The demand for goods (Z) depends on income (I), taxes (T), investment (I), and government spending (G): Z ≡ c 0 +c 1 (Y - T)+?I + G 供给的决定 The Determination of Supply ?假设企业不持有库存，因此对物品的供给等于生产Y。 Assume that firms do not hold inventories, so that the supply of goods is equal to production Y. ?回忆基本假设：企业在给定的价格下愿意供给任意数 量的物品。 Recall our basic assumption:Firms are willing to supply any amount of the good at a given price. ?那么，物品的供给将调整以恰好满足对物品的需求。 Then, the supply of goods (Y) will adjust to just meet the demand for goods (Z): Y = Z 均衡产出的决定 The Determination of Equilibrium Output ?物品市场中的一个均衡就是一对产出/收入(Y*)与需求 (Z*)的组合，满足： An equilibrium in the goods market is a pair of production/income (Y*) and demand (Z*), such that: ?给定收入Y*，Z*就是该收入引致的需求。 Given the income Y*, Z* is the demand induced by this income: Z* ≡ c 0 +c 1 (Y*-T)+?I + G ?给定需求Z*，Y*就是该需求引致的产出和收入。 Given the demand Z*, Y* is the production and income induced by this demand. Y* = Z* 均衡产出的决定 The Determination of Equilibrium Output ?总结这两个等式得到一个等式，即平衡 条件或平衡等式。 Summarizing these two equations leads to one equation, called an equilibrium condition or equilibrium equation: Y = c 0 +c 1 (Y - T)+?I + G 用以求解均衡产出。 which can be solved for the equilibrium output Y. 均衡产出的决定 The Determination of Equilibrium Output ?我们使用了同一符号Y来表示生产和收入。 We are using the same symbol Y for production and income. ?生产与收入恒等：他们是考虑GDP的两种不同 方式——一个从生产方，另一个从收入方。 Production and income are identically equal: They are the two way of looking at GDP – one from production side, the other from the income side. 7 三类方程（等式） Three Types of Equations ?恒等式Identities ?E.g., Y D ≡ Y – T, Z ≡ C + I + G ?行为方程Behavior Equations ?E.g., C = c 0 + c 1 (Y – T) ?均衡条件Equilibrium Conditions ?E.g., Y = c 0 +c 1 (Y - T)+?I + G 求解模型的三种工具 Three Tools For Solving A Model ?代数保证逻辑正确 Algebra to make sure that the logic is right ?图形建立直觉 Graphs to build the intuition ?语言解释结果 Words to explain the results 均衡产出：使用代数 The Equilibrium Output: Using Algebra Y = Z and Z ≡ c 0 +c 1 (Y - T)+?I + G ? Y = c 0 +c 1 (Y - T)+?I + G ? (1- c 1 )Y = c 0 +?I + G - c 1 T ? Y = [1/(1- c 1 )][c 0 +?I + G - c 1 T] 均衡产出：使用代数 The Equilibrium Output: Using Algebra ?其中第二项是物品需求中不依赖于产出 的那一部分。被称作自主支出。 The second term, [c 0 +?I + G - c 1 T], is that part of the demand for goods that does not depend on output. This term is called autonomous spending. 均衡产出：使用代数 The Equilibrium Output: Using Algebra ?其中第一项用来乘自主支出，被称作乘 数。 The first term, 1/(1-c 1 ), which multiplies autonomous spending, is called the multiplier. ?它是一个大于1的数。c 1 越接近于1，乘 数越大。 It is a number greater than one. The close c 1 is to one, the larger the multiplier. 均衡产出：使用代数 The Equilibrium Output: Using Algebra ?假设，在给定收入下，消费者增加消费。 Suppose that, for a given level of income, consumers decide to consume more. ?假定c 0 增加10亿美元。 Assume that c 0 increase by $1 billion. ?如果c 1 = 0.6，乘数就是2.5。 If c 1 = 0.6, the multiplier equals 1/(1-0.6)=2.5. ?于是产出增加25亿美元。 Then the output increases by, 2.5*$1 billion=$2.5 billion. 8 均衡产出：使用代数 The Equilibrium Output: Using Algebra ?自主支出的任何增加——投资上升、政 府支出上升或税收下降——将会提高产 出，数量大于对自主支出的直接效应。 Any increase in autonomous spending – from an increase in investment to an increase in government spending to a reduction in taxes – will increase output by more than its direct effect on autonomous spending. 均衡产出：使用图形 The Equilibrium Output: Using a Graph Production and Income (Y) Dem a n d ( Z ) Equilibrium point 45 o line Production Slope = 1 A ZZ Demand Autonomous spending Slope =c 1 Z* Y* 自主支出上升对产出的影响 The Effect of an Increase in Autonomous Spending on Output B Production and Income(Y) Dem a n d ( Z ) 45 o line Y* ZZ A Z* C D Y 1 * Z 1 * A’ ZZ’ $1 billion E 自主支出上升对产出的影响 The Effect of an Increase in Autonomous Spending on Output ?如果c 0 增加10亿美元，产出在n轮之后总的增加量等于 10亿美元乘以下列求和项： If c 0 increase by $1 billion, the total increase in production after n rounds equal $1 billion times the sum: 1 + c 1 + c 1 2 + … + c 1 n ?当n变得越来越大，产出的最终增加等于$1/(1-c 1 ) （10 亿美元）。 As n gets larger and larger, the eventual increase in output is $1/(1-c 1 ) billion. ?支出的初始增加触发了产出的连续增加。 The original increase in spending triggers successive increases in production. 均衡产出：使用语言 The Equilibrium Output: Using Words ?产出依赖于需求，需求依赖于收入，而收入本 身就等于产出。 Production depends on demand, which depend on income, which is itself equal to production. ?需求上升，例如政府或者消费者的支出增加， 导致产出上升和收入的相应增加。 An increase in demand, such as an increase in government or in consumer spending, leads to an increase in production and a corresponding increase in income. 均衡产出：使用语言 The Equilibrium Output: Using Words ?最终的结果是产出上升大于最初的需求移动， 因子等于乘数。 The end result is an increase in output that is larger than the initial shift in demand, by a factor equal to the multiplier. ?乘数的大小与消费倾向直接相关：消费倾向越 高，乘数越大。 The size of the multiplier is directly related to the value of the propensity to consume: the higher the propensity to consume, the higher the multiplier. 9 产出调整需要多长时间？ How Long Does It Take for Output to Adjust? ?理论暗含的瞬间调整是不太合乎实际的。 The instantaneous adjustment suggested by our theories does not seem very plausible. ?当一个企业面临需求增加时，它可能只是通过减少库存来满 足需求。 A Firm that faces an increase in demand may draw down its inventories to satisfy demand. ?当一个消费者工资上升时，它可能不急于改变消费。 A consumer who gets a raise at work may not adjust her consumption right away. ?正式地描述产出随时间的这种调整被称作调整的动态 （力）学。 Describing formally this adjustment of output over time is called the dynamics of adjustment. 产出调整需要多长时间？ How Long Does It Take for Output to Adjust? ?调整时间的长度依赖于企业如何调整其产出计 划，以及调整的频繁程度有多高。 How long the adjustment takes depends on how and how often firms revise their production schedule. ?企业越是经常地调整其产出计划，并且对以往 购买增加的反应更加充分，则调整越迅速。 The more often firms adjust their production schedule, and the larger the response of production to past increases in purchases, the faster the adjustment. 例子：消费者信心与1990－1991年的衰退 Example: Consumer Confidence and the 1990-1991 Recession ?在1990年第三季度，伊拉克入侵科威特之后，海湾战 争开始之前，美国的GDP增长率变成了负的，并在其 后的两个季度继续为负，这被称为1990－1991年的衰 退。 In the third quarter of 1990, after the invasion of Kuwait by Iraq but before the beginning of the Persian war, U.S. GDP growth turned negative and remained negative for the following two quarters, known as the 1990-1991 recession. ?消费者信心的下降是衰退背后的一个重要因素。 The decrease in consumer confidence was a major factor behind this recession. 例子：消费者信心与1990－1991年的衰退 Example: Consumer Confidence and the 1990-1991 Recession (7)(6)(5)= (2)-(4) (4)(3)(2)(1) Consumer Confidence Index Forecast error for c 0 (billions of 1992 dollars) Forecast error for GDP (billions of 1992 dollars) Forecast of GDP (billions of 1992 dollars) Change in GDP (billions of 1992 dollars) Real GDP (billions of 1992 dollars) Quarter 105-23-176,189196,1711990:2 47 -27 -88 -57 8 -30 -37 -1 776,027276,0741991:2 656,074-316,0471991:1 616,167-636,0781990:4 906,199-296,1421990:3 投资等于储蓄：考虑物品市场均衡的另一方法 Investment Equals Saving: An Alternative Way of Thinking About Goods-Market Equilibrium ?到目前为止我们考虑均衡都是关注的供给与需 求之间的相互作用。 Thus far we have thought about equilibrium in terms of interaction between the supply and the demand for goods. ?另一考虑均衡的等价方法是关注投资与储蓄。 An alternative – but equivalent – way of thinking about equilibrium focuses on investment and saving instead. 投资等于储蓄：考虑物品市场均衡的另一方法 Investment Equals Saving: An Alternative Way of Thinking About Goods-Market Equilibrium ?私人储蓄，也就是消费者的储蓄，等于可支配 收入减去消费。 Private saving (S), saving by consumers, is equal to their disposable income minus their consumption S ≡ Y D – C = Y – T – C = Y – T – c 0 – c 1 (Y – T) = -c 0 +(1 - c 1 )(Y - T) ?我们将(1-c 1 ) 称为储蓄倾向。 We call (1-c 1 ) the propensity to save. 10 投资等于储蓄：考虑物品市场均衡的另一方法 Investment Equals Saving: An Alternative Way of Thinking About Goods-Market Equilibrium ?公共储蓄等于税收减去政府支出。 Public saving (T – G), is equal to taxes minus government spending. 投资等于储蓄：考虑物品市场均衡的另一方法 Investment Equals Saving: An Alternative Way of Thinking About Goods-Market Equilibrium Y = C + I + G ? I = Y – C – G ? I = (Y – C –T)+ (T – G) ? I = S +(T-G) Investment = Private Saving + Public Saving 投资等于储蓄：考虑物品市场均衡的另一方法 Investment Equals Saving: An Alternative Way of Thinking About Goods-Market Equilibrium ?物品市场的均衡要求投资等于储蓄——私人储蓄加上 公共储蓄之和。 Equilibrium in the goods market requires that investment equals saving – the sum of private and public saving. ?这一考虑均衡的方法解释了为什么物品市场的均衡条 件被称作IS关系（投资和储蓄的首字母）。 This way of looking at equilibrium explains why the equilibrium condition for the goods market is called the IS relation, for “Investment equals Saving.” ?储蓄是通过产出的调整来满足既定的投资需求的。 Saving (S) adjusts to meet given investment demand (I) through the adjustment of production (Y). 储蓄悖论 The Paradox of Saving ?人们增加储蓄的企图导致产出下降而储 蓄不变。 Attempts by people to save more lead both to a decline in output and to unchanged saving. ?这一令人吃惊的结果组合被称为储蓄悖 论。 This surprising pair of results is known as the paradox of saving. 增加储蓄的结果 The Effect of Increasing Saving Production and Income(Y) I n v est m e nt (I ), Sa v i n g (S ) Y ?I Investment Saving Y’ 增加储蓄的结果 The Effect of Increasing Saving ?这一简单模型的结果在短期更适用。 The results of this simple model are of much relevance in the short run. ?但在中期或者长期，其他机制慢慢开始起作用，储蓄 率的提高有可能导致高储蓄和高产出。 But at the medium and the long run, other mechanisms come into play over time and an increase in the saving rate is likely lead to higher saving and higher income. ?在中期和长期鼓励储蓄的政策，在短期内却可能导致 衰退。 Policies that encourage saving may be good in the medium and the long run, but may lead to a recession in the short run. 11 政府真的能够选择他们想要的产出水平吗？ Can governments really choose the level of output they want? ?政府改变支出或税收谈何容易。 Changing government spending or taxes may be far from easy. ?支出和税收只能缓慢生效：消费者和企业可能担心预算赤字而改 变其行为。 The effects of spending and tax may happen slowly：consumers and firm may be scared of the budget deficit and change their behavior. ?保持理想的产出水平可能伴随者令人不快的副作用（例如加速通 胀），在中期内要维持这一产出可能很难。 Maintaining a desired level of output may come with unpleasant side effects, such as accelerating inflation, and may be unsustainable in the medium run. ?减税或者增加开支可能导致大规模的预算赤字和公共债务的积累 。这些债务在长期内有负作用。 Cutting tax or increasing government spending may lead to large budget deficits, and an accumulation of public debt. Such debt will have adverse implications in the long run. 总结 Summary ?GDP是消费、投资、政府支出、出口减 进口、库存投资之和。 GDP is the sum of consumption, plus investment, plus government spending, plus exports, minus imports, plus inventory investment. 总结 Summary ?在短期内，需求决定产出。产出等于收 入。收入决定需求。 In the short run, demand determines production. Production is equal to income. And income determines demand. 总结 Summary ?消费函数表示消费如何取决于可支配收入。 The consumption function shows how consumption depends on disposable income. ?消费倾向描述消费随着可支配收入的既定增加 而增加的大小。 The propensity to consume describes how much consumption increases for a given increase in disposable income. 总结 Summary ?均衡产出是供给（产出）和需求相等的点。 Equilibrium output is the point at which supply (production) equal demand. ?在均衡处，产出等于自主支出乘以乘数。 In equilibrium, output equals autonomous spending times the multiplier. ?消费者信心、投资和政府支出的增加或者税收 的下降都会增加短期内的产出。 Increases in consumer confidence, in investment demand, or in government spending, or decrease in taxes all increase equilibrium output in the short run. 总结 Summary ?表达物品市场均衡条件的另一方法是储 蓄等于投资。 An alternative way of stating the goods- market equilibrium condition is that investment must be equal to saving.