总需求与总供给(5)

AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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AD曲线为什么移动 Why the AD Curve Might Shift
▪ Changes in G
▪ Federal spending, e.g., defense ▪ State & local spending, e.g., roads, schools
P1
effect (I falls)
▪ the exchange-rate
effect (NX falls)
Y2
AD Y
Y1
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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AD曲线为什么移动 Why the AD Curve Might Shift
除了价格水平以外的因素 P 发生变化，AD曲线移动
A. A ten-year-old investment tax credit expires.
B. The U.S. exchange rate falls.
C. A fall in prices increases the real value of consumers’ wealth.
D. State governments replace their sales taxes with new taxes on interest, dividends, and capital gains.
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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古典经济学 Classical Economics
▪ 大多数经济学学家相信古典经济学描述了长期的
世界，但不说明短期。
▪ 在短期，名义变量的变动（如货币供给或价格水
平P)能影响真实变量（如真实GDP)
▪ 我们必须用新的模型来研究短期。
3
Three Facts About Economic Fluctuations
FACT 3: As output falls, unemployment rises.
12
10
Unemployment rate,
percent of labor force
8
6
4
2
0
1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
14,000
12,000 10,000
U.S. real GDP, billions of 2000 dollars
8,000 6,000 4,000 2,000
The shaded bars are recessions
0
1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
自然产量率
YN
Y
21
LRAS垂直的原因 Why LRAS Is Vertical
P
YN 取决于经济的劳动、 资本和自然资源，以
及生产技术 水平
P2
当价格水平 P上升时
P1
这些要素都不变，所以
不影响 YN.
(古典二分法Classical
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AS曲线 The Aggregate-Supply (AS) Curves
AS curve
P
说明了在某个价格水 平下企业生产和销售 的物品和劳务
LRAS
SRAS
AS is:
▪ 短期向上倾斜
▪ 长期是垂直的
Y
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
2
Three Facts About Economic Fluctuations
FACT 2: Most macroeconomic quantities fluctuate together.
2,500
2,000
B. The U.S. exchange rate falls. NX rises, AD curve shifts right.
C. A fall in prices increases the real value of consumers’ wealth. Move down along AD curve (wealth-effect).
Investment spending, billions of 2000 dollars
1,500
1,000
500
0
1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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古典经济学 Classical Economics
▪ 古典二分法（ Classical Dichotomy）
经济变量分为两类,
▪ 真实变量 – 产量、相对价格 ▪ 名义变量 – 用货币衡量的变量，名义GDP
▪ 货币中性（ neutrality of money）:
货币供给的变化只影响名义变量，不影响真实变 量。
( 投资i与利率成负相关.)
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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汇率效应 The Exchange-Rate Effect (P and NX )
▪ 假如价格水平上升 ▪ 利率上升 (利率效应). ▪ 外国投资者需要购买本国债券 ▪ 在外汇市场上，本国货币需求上升 ▪ 本国货币升值. ▪ 本国出口商品变贵了，进口商品便宜了
P
Y = C + I + G + NX
P2
假定政府购买不变
.
P1 AD
Y
Y2
Y11
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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财富效应 The Wealth Effect (P and C )
假设价格水平上升
▪ 同样的货币买更少的物品与劳务，真实财富下降。 ▪ 人们感觉变穷了.
D. State governments replace sales taxes with new taxes
on interest, dividends, and capital gains.
C rises, AD shifts right.
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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Introduction, continued
▪ 解释经济波动的理论有很多.
▪ AD-AS模型是研究经济波动的一种方法。
▪ 这个模型不同于之前学习的描述长期的古典经济
学理论。
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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总需求曲线 The Aggregate-Demand (AD) Curve
P
AD curve 在经
济中，每个价格 价格下物品与劳
P2
务的需求量.
P1 AD
Y
Y2
Y1
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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需求曲线向右下方倾斜 Why the AD Curve Slopes Downward
▪ Stock market boom/crash ▪ Preferences re: consumption/saving tradeoff ▪ Tax hikes/cuts
▪ Changes in I
▪ Firms buy new computers, equipment, factories ▪ Expectations, optimism/pessimism ▪ Interest rates, monetary policy ▪ Investment Tax Credit or other tax incentives
如: 股票市场的繁荣使家庭感 觉富裕了，结果增加消费，P1 AD曲线向右移动。
AD2 AD1
Y
Y1
Y2
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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AD曲线为什么移动 Why the AD Curve Might Shift
▪ Changes in C
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长期AS曲线：LRAS The Long-Run Aggregate-Supply Curve (LRAS)
自然产出率natural rate P of output (YN. ）
LRAS
YN ：也被称作潜在产出 （ potential output ）或充分就业的产出 （full-employment output）.
dichotomy)
LRAS YN
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
结果: C 下降
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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利率效应 The Interest-Rate Effect (P and I )
假如物价水平上升.
▪ 买物品与劳务需要更多的钱
▪ 为了获得这些钱，人们卖出债券和其他资产
▪ 市场利率上升
结果: I 下降
▪ Changes in NX
▪ Booms/recessions in countries that buy our exports. ▪ Appreciation/depreciation resulting from
international speculation in foreign exchange market
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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ACTIVE LEARNING 1
Answers
A. A ten-year-old investment tax credit expires. I falls, AD curve shifts left.
第9讲 总需求（AD)与总供给(AS)
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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Introduction
▪ 在长期，真实GDP每年平均增长3%。
▪ 在短期，GDP是波动的。 ▪ 衰退（Recessions）: 真实收入下降，失业率上
升。
▪ 萧条（Depressions）: 严重的衰退。
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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ACTIVE LEARNING 1
The Aggregate-Demand curve
What happens to the AD curve in each of the following scenarios?
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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总需求与总供给模型
The Model of Aggregate Demand
and Aggregate Supply
P The price
levele model determines the
结果: NX 下降
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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总结：AD曲线向右下方倾斜 The Slope of the AD Curve: Summary
当价格水平P上升时
P
P2
▪ the wealth effect (C
falls)
▪ the interest-rate
▪ 短期的经济波动，就是经济周期（business cycles).
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
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Three Facts About Economic Fluctuations
FACT 1: Economic fluctuations are irregular and unpredictable.
P1
Aggregate Supply”
eq’m price level
“Aggregate
Demand”
AD
and eq’m output (real GDP).
AGG2R02E1G/2/A7TE DEMAND AND AGGREGATE SUPPLY
Y Y1
Real GDP, the quantity of output