短期 The short Run 物品市场 The Goods market 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。 第3章 In the short run, demand Chapter 3 determines output. Many factors affect demand. from consumer confidence to fiscal and monetary Policy. 物品市场 物品市场 The Goods market 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 当经济学家考虑经济活动的逐年变化时,他们 ◆生产的变化导致收入的变化。 When economists think about year-to-year Changes in production lead to changes in income. movements in economic activity, they focus on ◆收入的变化导歌对物品需求的变化。 the interaction between production, income, and And changes in income lead to changes in the demand for goods. GDP的构成 GDP的构成 The Composition of GDP The Composition of GDP 年政头图表延因素测贵则买食物,联 ◆消费 Consumption(O by firms depend on differer ◆投资 Investment( actors than do purchases of food by consumers, of urchases of new combat airplanes by the federal ◆政府支出 Government Spending(G government. 玺物仗金对这些、物的有的发 ◆净出口 Net Exports(X-Q) ◆库存投资 Inventory Investment(U) If we are to think about what determines the demand roduction( GDP) from the point of view of th ifferent goods being produced, and the different buvers for these goo
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 (Is)
消费 投资 Consumption Investment ◆消费代表消费者购买的物品与服务。 ◆投资有时被称作固定投资,以区别于库存投资 Consumption()represent goods and Investment (D) is sometimes called fixed investment to distinguish it from inventory services purchased by consumers. investment ◆食物,机票,度假,新车 ◆投资是非居民投资和居民投资之和。前者指企 Food, airline tickets, vacations, new cars,. 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 政府支出 Investment Government Spending ◆企业购买机器或者厂房是为了能够在将 ◆政府支出代表联邦、州和地方政府购买的物品和服务 来生产更多的产出 goods and services by the federal, state, and local Firms buy machines or plants to be able to product more output in the future. 物品包括飞机测办公设备。 ◆人们购买房屋或者公寓是为了未来得到 服务包括政府雇员提供的服务 住房服务 People buy houses or apartments to get 实医占要民众从为是取扇买了取最员提供的原务 housing services in the future. h图bgp providing these services to the publie, free of charge. 政府支出 净出口 Government Spending Net Exports ◆G不包括政府转移支付,例如医疗保险或者社 保险,也不包括政府支付的债务利息 物和服雾:者取购买的外 G does not include government transfers, such urchases of foreign goods and services by U.s. as Medicare or Social Security. nor interest consumers. U.S. firms, and the U.S. ments on the government deh overnment 些属于政府的开支,但他们不是对于物 ◆出口代表外国购买的美国的物品和服务 Exports(X)represents the purch Although these are clearly government goods and services by foreigners. xpenditures, they are not purchases of goods ◆出口和进口之差被称作净出口,成贸易余额 and services The difference between exports and imports, (X 2), is called net exports, or the trade balance
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
净出口 库存投资 Net Exports Inventory Investment ◆如果出口大于进口,一国就有了贸易盈 ◆一些物品是某年生产的,但不在该年出售,而 余 出售。一些物品是某年出售的,但却是往年生 me of the goods produced in a given year ar If exports exceed imports, a country is in that year, but sold in later vear. Some of the said to run a trade surplus. sold in a given year may have been produced in an ◆如果出口小于进口,该国就有了贸易赤 earlier vear ◆某年的物品生产量与出售量之差被称作库存投资。 If exports are less than imports, the in a given year-equivalently, between production and country is said to run a trade deficit sales-is called inventory investment and is denoted I 库存投资 美国GDP的构成 The Composition of Inventory Investment U. S. GDP, 1998 Billions of dollars Percent of gdp ◆如果生产大于销售,企业积累库存。库存投资 是正的。 GDP(n If produce exceeds sales, firm accumulate tion inventories. Inventory investment is positive Investment (n) Nonresidential 939 ◆如果生产小于销售,企业减少库存。库存投资 Residential 为负。 Government Spending(G) 1488 If produce is less than sales, firms decrease Not Exports tment is negative Exports(X) Imports(Q 1112 Inventory Investment(s) 物品的需求 基本假设 The Demand for Goods Basic Assumptions 对物品的总需求可以写成: ◆假设1:所有企业生产相同的物品,它既可以为消费者 来消贵,也可以被企业用来投资, The Total demand for goods(2) can be Assumption 1: All firms produce the same good, which written a can be used by consumers for consumption, by firms for invest Z=C+I+G+X-o ◆有了这一简化,我们只需买关注一个市场“该物 品的市场—考虑在这个市场中供给和需求的决定因 with this simplification, we market-the market for the" good-and think and in that mar
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 Is. 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 (IS) 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
基本假设 基本假设 Basic Assumption 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。 ◆这一假设只在短期内成立 Assumption 2: Firms are willing to supply any This assumption in valid only in the short mount of the good at a given price. run ◆换句话说,物品的供给在价格P上是完全富于 ◆当我们转而研究中期时,我们需要放弃 In other words, the supply of goods is 这一假设 completely elastic at price P When we move to the study of the 假设允许我们集中关注需求在决定产出上 medium run, we shall need to give up this assumption. This a tion will allow us to focus on t role of demand in the determination of output 基本假设 消费的决定因素 The Determination of Basic Assumptions Consumption ◆假设3:经济是封知的,即它不与世界的其他 部分进行贸易 大含是像合解4要 Assumption 3: The economy is closed, that it does no trade with the rest of the world The main determinant of consumption(O)is s ◆出口与进口都等于零 income that remains once consumers have rec Both exports and imports are equal to zero. transfers from the government and paid their C-C(YD) ◆函数C(D)被称作消费函数 Z≡C+I+G The function C(YD) is called the consumption function. 消费的决定因素 消费的决定因素 The determination of The determination of Consumption Consumption ◆假定消费函数是线性的。 ◆经济学家把这样的方程叫做行为方程,因为这 Assume that the consumption function is a linear 方程反映了某些方面的行为这里是消费 者的行为 C-co+c,YD Economists call such an equation a behavioral ◆参数c被称作(边际)消费倾向。0<c<1 equation, to indicate that the equation reflect The parameter c, is called the(marginal ) propensity to ome aspect of behavior-in this case, the consume. O<c<l ◆参数c表示人们当年的可支配收入等于零时的消费 behavior of consumers disposable income in the current year were equal to 入为零,人们通过动用情一卖掉现有资产来保持 People have positive consumption if their incom
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 (YD), the income that remains once consumers have received transfers from the government and paid their taxes. C = C(YD) (+) 函数C(YD) 被称作消费函数。 The function C(YD) 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 = c0 + c1YD 参数c1被称作（边际）消费倾向。 0<c1<1。 The parameter c1 is called the (marginal ) propensity to consume. 0<c1<1. 参数c0 表示人们当年的可支配收入等于零时的消费。 The parameter c0 is what people would consume if their disposable income in the current year were equal to zero. c0>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
消费的决定因素 消费的决定因素 The determination of The determination of Consumption Consumption ◆可支配收入等于 Disposable income is given by Yn≡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 Slope = C1 ◆这是一个恒等式。 This equation is an identity Disposable Income, Y C=Co+cO 为什么价格不再是 投资的决定因素 决定消费的主要因素? The Determination of Investment ◆在微观经济学中,消费者对某一物品的 ◆我们将投资视为给定,写成 需求取决于它的相对价格 (relative price We shall take investment as given, and ,即它相对于其他物品的价格。 write ◆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 leve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 come)——的影响当中。 投资的决定因素 政府支出的决定因素 The Determination of The determination of Investment Government Spending ◆模型有两类变量 ◆我们将政府支出,连同税收一起,视作 Models have two types of variables 外生的 得封票依干生要的其他变量,固而在桃型内 We shall take government spending(G), ome variables depend on other variables in the together with taxes(n), as exogenous. nodel, and are therefore explained within the model 如,费Eg, consumpton(O 变量不在模型内进行解释而是给定的一 变量。 Other variables are not explained within le model but are instead taken as givel Exogenous variables. ◆例如,投簧Eg, investment(n
5 消费的决定因素 The Determination of Consumption Disposable Income,YD Consumption, c Consumption function C = c0 + C1YD Slope = c1 c0 消费的决定因素 The Determination of Consumption 可支配收入等于： Disposable income is given by YD ≡ 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 = c0 + c1(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