第二讲IS- LM曲线

c 0 e G c1T 1 c1 i y d d
Deriving the IS Curve
3. IS曲线的移动
c 0 e G c1T 1 c1 i y d d
IS曲线截距的变动
c 0 e G c1T d
IS曲线斜率的变动
部分任何一项的变动
§ 3、消费理论
1. 消费函数
消费与收入的依存关系称为消费函数。 1）. 影响消费或需求的因素：
• 影响消费的因素有很多种，价格水平、收入水平、
个人偏好、预期、利率、分配等
• 古典理论认为主要是价格 • 凯恩斯认为主要是家庭收入
2）. 家庭消费函数：
c c( yD )
这一函数式体现了凯恩斯对于收入的重视，从而将收 入作为宏观经济分析的核心变量，(behavioral equation)
c = 300 + 0.75y
8）. 线性消费函数图
c
入不敷出
入大于出 B
曲线的斜率为边 际消费倾向
c= c0+c1 yD
收支平衡点
c0
45o
o
yD
Consumption and Disposable Income
C C(YD ) YD Y T C c0 c1 (Y T )
上式就是IS曲线
进一步假定投资函数为：
I =e–di
暂时不与y 相关
y C I G c0 c1( y T ) e di G
c0 e G c1T c1 y di
c 0 e G c1T di y 1 c1 1 c1
The Effects of an Increase in Autonomous Spending on Output
The Paradox of Saving
When consumers save more, spending decreases and equilibrium output is lower. Attempts by people to save more lead both to a decline in output and to unchanged saving. This surprising pair of results is known as the paradox of saving (or the paradox of thrift).
第二讲 IS-LM模型
主要内容：
商品市场与IS关系 货币市场与LM关系 IS-LM 模型与宏观经济政策
第一章 商品市场与IS关系 § 1、均衡产出的概念
和总需求相等的产出称为均衡产出。 （总产出=总产量=国民收入，它们取 决于总需求，但并不等于总需求）
Y＝C＋S
收入Y
Y＝C＋I
居民
储蓄S Y＝C＋S＋T 税收T Y＝C＋S＋T＋M 进口M
§5、IS 关系
1. 古典的两分法（dichotomy)
产品市场与货币市场互不相关（中性货币）
凯恩斯通过在投资函数里引入利率变量打破 了两分法 • 利率是连接货币市场与商品市场的桥梁 • 利率由货币市场决定 • 通过影响投资来影响商品市场
2. IS曲线的推导
In this sector, we capture the effects of two factors affecting investment: The level of sales (+) The interest rate (-)
Saving: A part of after-tax income that is not spent. A flow
Wealth: A stock variable at a given point in time. Equal to financial assets minus financial liabilities Investment: The purchase of new capital goods Financial investment: purchase of shares or other financial assets
2. 投资函数
在讨论简单国民收入决定理论时，假定：
I I
Note: Distinction Exogenous , Endogenous
在讨论IS模型时，将放松这一假定：
I =e–dr
3. 政府购买
Government spending, G, together with taxes, T, describes fiscal policy—the choice of taxes and spending by the government. We shall assume that G and T are also exogenous.
7,064
1,692 1,246 446 1,839 329 1,097 1,468 58
69
17 12 5 18 3 11 14 1
3. 4.
Government spending (G) Net exports = X - M
Exports (X) Imports (IM) 5. Inventory investment
假定投资不再是常数，投资函数为：
I I (Y , i )
Taking into account the investment relation above, the equilibrium condition in the goods market becomes:
Y C(Y T ) I (Y , i ) G
production = income =Y = demand (Z)
Y Z
两部门时： 三部门时：
I=S
I S (T G )
I = S + （T - G）+（M - X）
四部门时：
Demand, production and income
Production
Demand
Income
2. 均衡产出
Assume:
One bond market One interest rate
It is clear that you should hold both money and bonds. In what proportions should you do so? This will depend mainly on two variables:
Table 2-1 The Composition of U.S. GDP, 2001
Billions of dollars GDP (Y) 10,208 Percent of GDP 100
1.
2.
Consumption (C)
Investment (I) Nonresidential Residential
§1. 货币需求
A Scenario…
Two financial assets to choose from:
Money: Used for transactions (currency and checkable deposits), good liquidity, no interest Bonds: Cannot be used for transactions and pays a positive interest rate (i), bad liquidity
Your level of transaction:
You want to have enough money, on average, to avoid having to sell bonds to get money too often The interest rate:
The only reason to hold any of your wealth in bonds is that they pay interest. If bonds paid no interest, you would hold all of your wealth in money. The higher the interest rate, the more you will be willing to incur the hassle and the costs associated with buying and selling bonds.
The term (1c1) is called the propensity to save.
1/(1c1) 是投资乘数
乘数效应
Using a Graph
Z (c0 I G c1T ) c1Y
Equilibrium in the Goods Market
Using a Graph
Is the Government Omnipotent? A Warning
Changing government spending or taxes may be far from easy. The responses of consumption, investment, imports, etc, are hard to assess with much certainty. Anticipations are a likely matter. Achieving a given level of output may come with unpleasant side effects. Budget deficits and public debt may have adverse implications in the long run.