曼昆《经济学原理》(宏观经济学分册)英文原版PPT课件——33aggregate_demand.ppt

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1、12 SHORT-RUN ECONOMIC FLUCTUATIONSCopyright 2004 South-Western33Aggregate Demand and Aggregate SupplyCopyright 2004 South-WesternShort-Run Economic FluctuationsEconomic activity fluctuates from year to year.In most years production of goods and services rises.On average over the past 50 years,produc

2、tion in the U.S.economy has grown by about 3 percent per year.In some years normal growth does not occur,causing a recession.Copyright 2004 South-WesternShort-Run Economic FluctuationsA recession is a period of declining real incomes,and rising unemployment.A depression is a severe recession.Copyrig

3、ht 2004 South-WesternTHREE KEY FACTS ABOUT ECONOMIC FLUCTUATIONSEconomic fluctuations are irregular and unpredictable.Fluctuations in the economy are often called the business cycle.Most macroeconomic variables fluctuate together.As output falls,unemployment rises.Figure 1 A Look At Short-Run Econom

4、ic FluctuationsBillions of1996 DollarsReal GDP(a)Real GDP$10,0009,0008,0007,0006,0005,0004,0003,0002,00019651970197519801985199019952000Copyright 2004 South-WesternCopyright 2004 South-WesternTHREE KEY FACTS ABOUT ECONOMIC FLUCTUATIONSMost macroeconomic variables fluctuate together.Most macroeconomi

5、c variables that measure some type of income or production fluctuate closely together.Although many macroeconomic variables fluctuate together,they fluctuate by different amounts.Figure 1 A Look At Short-Run Economic FluctuationsBillions of1996 Dollars(b)Investment Spending$1,8001,6001,4001,2001,000

6、80060040020019651970197519801985199019952000Investment spendingCopyright 2004 South-WesternCopyright 2004 South-WesternTHREE KEY FACTS ABOUT ECONOMIC FLUCTUATIONSAs output falls,unemployment rises.Changes in real GDP are inversely related to changes in the unemployment rate.During times of recession

7、,unemployment rises substantially.Figure 1 A Look At Short-Run Economic FluctuationsPercent ofLabor Force(c)Unemployment Rate02468101219651970197519801985199019952000Unemployment rateCopyright 2004 South-WesternCopyright 2004 South-WesternEXPLAINING SHORT-RUN ECONOMIC FLUCTUATIONSHow the Short Run D

8、iffers from the Long RunMost economists believe that classical theory describes the world in the long run but not in the short run.Changes in the money supply affect nominal variables but not real variables in the long run.The assumption of monetary neutrality is not appropriate when studying year-t

9、o-year changes in the economy.Copyright 2004 South-WesternThe Basic Model of Economic FluctuationsTwo variables are used to develop a model to analyze the short-run fluctuations.The economys output of goods and services measured by real GDP.The overall price level measured by the CPI or the GDP defl

10、ator.Copyright 2004 South-WesternThe Basic Model of Economic Fluctuations The Basic Model of Aggregate Demand and Aggregate SupplyEconomist use the model of aggregate demand and aggregate supply to explain short-run fluctuations in economic activity around its long-run trend.Copyright 2004 South-Wes

11、ternThe Basic Model of Economic Fluctuations The Basic Model of Aggregate Demand and Aggregate SupplyThe aggregate-demand curve shows the quantity of goods and services that households,firms,and the government want to buy at each price level.Copyright 2004 South-WesternThe Basic Model of Economic Fl

12、uctuations The Basic Model of Aggregate Demand and Aggregate SupplyThe aggregate-supply curve shows the quantity of goods and services that firms choose to produce and sell at each price level.Figure 2 Aggregate Demand and Aggregate Supply.Quantity ofOutputPriceLevel0AggregatesupplyAggregatedemandEq

13、uilibriumoutputEquilibriumprice levelCopyright 2004 South-WesternCopyright 2004 South-WesternTHE AGGREGATE-DEMAND CURVEThe four components of GDP(Y)contribute to the aggregate demand for goods and services.Y=C+I+G+NXFigure 3 The Aggregate-Demand Curve.Quantity ofOutputPriceLevel0AggregatedemandPYY2P

14、21.A decreasein the pricelevel.2.increases the quantity ofgoods and services demanded.Copyright 2004 South-WesternCopyright 2004 South-WesternWhy the Aggregate-Demand Curve Is Downward SlopingThe Price Level and Consumption:The Wealth EffectThe Price Level and Investment:The Interest Rate EffectThe

15、Price Level and Net Exports:The Exchange-Rate EffectCopyright 2004 South-WesternWhy the Aggregate-Demand Curve Is Downward SlopingThe Price Level and Consumption:The Wealth EffectA decrease in the price level makes consumers feel more wealthy,which in turn encourages them to spend more.This increase

16、 in consumer spending means larger quantities of goods and services demanded.Copyright 2004 South-WesternWhy the Aggregate-Demand Curve Is Downward SlopingThe Price Level and Investment:The Interest Rate EffectA lower price level reduces the interest rate,which encourages greater spending on investm

17、ent goods.This increase in investment spending means a larger quantity of goods and services demanded.Copyright 2004 South-WesternWhy the Aggregate-Demand Curve Is Downward SlopingThe Price Level and Net Exports:The Exchange-Rate EffectWhen a fall in the U.S.price level causes U.S.interest rates to

18、fall,the real exchange rate depreciates,which stimulates U.S.net exports.The increase in net export spending means a larger quantity of goods and services demanded.Copyright 2004 South-WesternWhy the Aggregate-Demand Curve Might ShiftThe downward slope of the aggregate demand curve shows that a fall

19、 in the price level raises the overall quantity of goods and services demanded.Many other factors,however,affect the quantity of goods and services demanded at any given price level.When one of these other factors changes,the aggregate demand curve shifts.Copyright 2004 South-WesternWhy the Aggregat

20、e-Demand Curve Might ShiftShifts arising from ConsumptionInvestmentGovernment PurchasesNet ExportsCopyright 2004 South-WesternShifts in the Aggregate Demand CurveQuantity ofOutputPriceLevel0Aggregatedemand,D1P1Y1D2Y2 Copyright 2004 South-WesternTHE AGGREGATE-SUPPLY CURVEIn the long run,the aggregate

21、-supply curve is vertical.In the short run,the aggregate-supply curve is upward sloping.Copyright 2004 South-WesternTHE AGGREGATE-SUPPLY CURVEThe Long-Run Aggregate-Supply CurveIn the long run,an economys production of goods and services depends on its supplies of labor,capital,and natural resources

22、 and on the available technology used to turn these factors of production into goods and services.The price level does not affect these variables in the long run.Figure 4 The Long-Run Aggregate-Supply CurveQuantity ofOutputNatural rateof outputPriceLevel0Long-runaggregatesupplyP21.A changein the pri

23、celevel.2.does not affect the quantity of goods and services supplied in the long run.PCopyright 2004 South-WesternCopyright 2004 South-WesternTHE AGGREGATE-SUPPLY CURVEThe Long-Run Aggregate-Supply CurveThe long-run aggregate-supply curve is vertical at the natural rate of output.This level of prod

24、uction is also referred to as potential output or full-employment output.Copyright 2004 South-WesternWhy the Long-Run Aggregate-Supply Curve Might ShiftAny change in the economy that alters the natural rate of output shifts the long-run aggregate-supply curve.The shifts may be categorized according

25、to the various factors in the classical model that affect output.Copyright 2004 South-WesternWhy the Long-Run Aggregate-Supply Curve Might ShiftShifts arising LaborCapitalNatural ResourcesTechnological KnowledgeFigure 5 Long-Run Growth and InflationQuantity ofOutputY1980AD1980AD1990Aggregate Demand,

26、AD2000PriceLevel0Long-runaggregatesupply,LRAS1980Y1990LRAS1990Y2000LRAS2000P19801.In the long run,technological progress shifts long-run aggregate supply.4.andongoing inflation.3.leading to growthin output.P1990P20002.and growth in the money supply shifts aggregate demand.Copyright 2004 South-Wester

27、nCopyright 2004 South-WesternA New Way to Depict Long-Run Growth and InflationShort-run fluctuations in output and price level should be viewed as deviations from the continuing long-run trends.Copyright 2004 South-WesternWhy the Aggregate-Supply Curve Slopes Upward in the Short RunIn the short run,

28、an increase in the overall level of prices in the economy tends to raise the quantity of goods and services supplied.A decrease in the level of prices tends to reduce the quantity of goods and services supplied.Figure 6 The Short-Run Aggregate-Supply CurveQuantity ofOutputPriceLevel0Short-runaggrega

29、tesupply1.A decreasein the pricelevel.2.reduces the quantityof goods and servicessupplied in the short run.YPY2P2Copyright 2004 South-WesternCopyright 2004 South-WesternWhy the Aggregate-Supply Curve Slopes Upward in the Short RunThe Misperceptions TheoryThe Sticky-Wage TheoryThe Sticky-Price Theory

30、Copyright 2004 South-WesternWhy the Aggregate-Supply Curve Slopes Upward in the Short RunThe Misperceptions TheoryChanges in the overall price level temporarily mislead suppliers about what is happening in the markets in which they sell their output:A lower price level causes misperceptions about re

31、lative prices.These misperceptions induce suppliers to decrease the quantity of goods and services supplied.Copyright 2004 South-WesternWhy the Aggregate-Supply Curve Slopes Upward in the Short RunThe Sticky-Wage TheoryNominal wages are slow to adjust,or are“sticky”in the short run:Wages do not adju

32、st immediately to a fall in the price level.A lower price level makes employment and production less profitable.This induces firms to reduce the quantity of goods and services supplied.Copyright 2004 South-WesternThe Sticky-Price TheoryPrices of some goods and services adjust sluggishly in response

33、to changing economic conditions:An unexpected fall in the price level leaves some firms with higher-than-desired prices.This depresses sales,which induces firms to reduce the quantity of goods and services they produce.Copyright 2004 South-WesternWhy the Short-Run Aggregate-Supply Curve Might ShiftS

34、hifts arising LaborCapitalNatural Resources.Technology.Expected Price Level.Copyright 2004 South-WesternWhy the Aggregate Supply Curve Might ShiftAn increase in the expected price level reduces the quantity of goods and services supplied and shifts the short-run aggregate supply curve to the left.A

35、decrease in the expected price level raises the quantity of goods and services supplied and shifts the short-run aggregate supply curve to the right.Figure 7 The Long-Run EquilibriumNatural rateof outputQuantity ofOutputPriceLevel0Short-runaggregatesupplyLong-runaggregatesupplyAggregatedemandAEquili

36、briumpriceCopyright 2004 South-WesternFigure 8 A Contraction in Aggregate DemandQuantity ofOutputPriceLevel0Short-run aggregatesupply,ASLong-runaggregatesupplyAggregatedemand,ADAPYAD2AS21.A decrease inaggregate demand.2.causes output to fall in the short run.3.but over time,the short-runaggregate-su

37、pplycurve shifts.4.and output returnsto its natural rate.CP3BP2Y2Copyright 2004 South-WesternCopyright 2004 South-WesternTWO CAUSES OF ECONOMIC FLUCTUATIONSShifts in Aggregate DemandIn the short run,shifts in aggregate demand cause fluctuations in the economys output of goods and services.In the lon

38、g run,shifts in aggregate demand affect the overall price level but do not affect output.Copyright 2004 South-WesternTWO CAUSES OF ECONOMIC FLUCTUATIONS An Adverse Shift in Aggregate SupplyA decrease in one of the determinants of aggregate supply shifts the curve to the left:Output falls below the n

39、atural rate of employment.Unemployment rises.The price level rises.Figure 10 An Adverse Shift in Aggregate SupplyQuantity ofOutputPriceLevel0Aggregate demand3.and the price level to rise.2.causes output to fall.1.An adverse shift in the short-run aggregate-supply curve.Short-runaggregatesupply,ASLon

40、g-runaggregatesupplyYAPAS2BY2P2Copyright 2004 South-WesternCopyright 2004 South-WesternThe Effects of a Shift in Aggregate SupplyStagflationAdverse shifts in aggregate supply cause stagflationa period of recession and inflation.Output falls and prices rise.Policymakers who can influence aggregate de

41、mand cannot offset both of these adverse effects simultaneously.Copyright 2004 South-WesternThe Effects of a Shift in Aggregate SupplyPolicy Responses to RecessionPolicymakers may respond to a recession in one of the following ways:Do nothing and wait for prices and wages to adjust.Take action to in

42、crease aggregate demand by using monetary and fiscal policy.Figure 11 Accommodating an Adverse Shift in Aggregate SupplyQuantity ofOutputNatural rateof outputPriceLevel0Short-runaggregatesupply,ASLong-runaggregatesupplyAggregate demand,ADP2APAS23.whichcauses theprice level to rise further.4.but keep

43、s outputat its natural rate.2.policymakers canaccommodate the shiftby expanding aggregatedemand.1.When short-run aggregatesupply falls.AD2CP3Copyright 2004 South-WesternCopyright 2004 South-WesternSummaryAll societies experience short-run economic fluctuations around long-run trends.These fluctuatio

44、ns are irregular and largely unpredictable.When recessions occur,real GDP and other measures of income,spending,and production fall,and unemployment rises.Copyright 2004 South-WesternSummaryEconomists analyze short-run economic fluctuations using the aggregate demand and aggregate supply model.Accor

45、ding to the model of aggregate demand and aggregate supply,the output of goods and services and the overall level of prices adjust to balance aggregate demand and aggregate supply.Copyright 2004 South-WesternSummaryThe aggregate-demand curve slopes downward for three reasons:a wealth effect,an inter

46、est rate effect,and an exchange rate effect.Any event or policy that changes consumption,investment,government purchases,or net exports at a given price level will shift the aggregate-demand curve.Copyright 2004 South-WesternSummaryIn the long run,the aggregate supply curve is vertical.The short-run

47、,the aggregate supply curve is upward sloping.The are three theories explaining the upward slope of short-run aggregate supply:the misperceptions theory,the sticky-wage theory,and the sticky-price theory.Copyright 2004 South-WesternSummaryEvents that alter the economys ability to produce output will

48、 shift the short-run aggregate-supply curve.Also,the position of the short-run aggregate-supply curve depends on the expected price level.One possible cause of economic fluctuations is a shift in aggregate demand.Copyright 2004 South-WesternSummaryA second possible cause of economic fluctuations is a shift in aggregate supply.Stagflation is a period of falling output and rising prices.