lecture 20 planned aggregate expenditure and output€¦ · planned aggregate expenditure and...
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Economics 2 Professor Christina Romer Spring 2018 Professor David Romer
LECTURE 20 PLANNED AGGREGATE EXPENDITURE AND OUTPUT
April 5, 2018
I. OVERVIEW OF SHORT-RUN FLUCTUATIONS
A. GDP
B. Unemployment
II. THE KEY ROLE OF DEMAND
A. Terminology
B. Evidence
C. Source
III. PLANNED AGGREGATE EXPENDITURE (PAE)
A. Components
B. Short run versus long run
IV. DETERMINANTS OF EACH COMPONENT OF PAE
A. Planned investment (Ip)
B. Government spending (G) and net exports (NX)
C. Consumption (C)
1. Factors that affect consumption
2. The “consumption function”
V. DETERMINANTS OF OUTPUT IN THE SHORT RUN
A. Equilibrium condition (Y = PAE)
B. Expenditure line (PAE)
C. Equilibrium and how the economy gets there
D. Short-run versus long-run equilibrium
E. Discussion
VI. SHIFTS IN THE EXPENDITURE LINE
A. Crucial determinant of short-run fluctuations
B. Example: A decline in autonomous consumption
C. The multiplier effect
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LECTURE 20 Planned Aggregate Expenditure and Output
April 5, 2018
Economics 2 Christina Romer Spring 2018 David Romer
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Announcements
• We have handed out Problem Set 5.
• It is due at the start of lecture on Thursday, April 12th.
• Problem set work session next Monday, April 9th, 6:00–8:00 p.m. in 648 Evans.
• Research paper reading for next time.
• Romer and Romer, “The Macroeconomic Effects of Tax Changes.”
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I. OVERVIEW OF SHORT-RUN FLUCTUATIONS
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Real GDP in the United States, 1950–2017
Source: FRED (Federal Reserve Economic Data); data from Bureau of Economic Analysis.
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Short-Run Fluctuations
• Times when output moves above or below potential (booms and recessions).
• Recessions are costly and very painful to the people affected.
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The U.S. Unemployment Rate, 1948–2018
Source: FRED; data from Bureau of Labor Statistics.
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Real GDP Growth (Percent, Red) and Change in the Unemp. Rate (Percentage Points, Blue), 1961–2017
Source: FRED; data from Bureau of Economic Analysis and Bureau of Labor Statistics.
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II. THE KEY ROLE OF DEMAND
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Key Determinant of Output in the Short Run
• In the short run, aggregate output is determined by demand.
• Three terms that mean the same thing:
• Planned aggregate expenditure
• Planned spending
• Planned aggregate demand
• All three terms refer to the total amount that people in the economy plan to buy (or spend).
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Evidence on the Key Role of Demand
• Historical experience.
• Academic research.
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Why is Output Determined by Demand in the Short Run?
• Nominal rigidities (inflation doesn’t change substantially in the short run).
• Due to limited information, menu costs, long-term contracts, or other factors.
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III. PLANNED AGGREGATE EXPENDITURE
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Components of Planned Aggregate Expenditure (PAE)
• Consumption (C)
• Planned investment (Ip)
• Government purchases (G)
• Net exports (NX)
PAE = C + Ip + G + NX
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Short Run versus Long Run
• In the short run:
• PAE can be more than, less than, or equal to Y*.
• Output responds to match PAE.
• In the long run:
• Output is at Y* (determined by normal technology, capital, and employment).
• PAE adjusts to equal Y*.
• Movement in r brings this about.
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IV. DETERMINANTS OF EACH COMPONENT OF PAE
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Determinants of Planned Investment (Ip)
• Real interest rate (r).
• Expectations (“animal spirits”).
• We talk about “planned investment” because we are leaving out the unplanned investment in inventories that happens when PAE is different from actual output.
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Determinants of Government Purchases (G)
• Politics.
• Wars, natural disasters.
We take G as given.
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Determinants of Net Exports (NX)
• For now we are assuming they are just given.
• Will discuss the economic determinants later in the course.
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Determinants of Consumption (C)
• Real interest rate (r): A rise in the real interest rate reduces consumption.
• Expectations (“consumer confidence”)
• Wealth: A rise in wealth increases consumption.
• Disposable income (Y − T): A rise in disposable income increases consumption (but by less than the amount of the increase in disposable income).
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Consumption and Disposable Income
• Aggregate income: Same as aggregate output (Y)
• Aggregate tax payments: Same as government tax revenues (T)
• Aggregate disposable income: Y−T
• Consumption function: C = f(Y−T)
• Sometimes written in the particular form: C = C� + c·(Y−T)
(where C� is positive and c is between 0 and 1)
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Consumption Function C = C + c·(Y−T)
slope = c
Y−T
C
C
C
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Consumption Function C = C + c·(Y−T)
• Autonomous consumption: The part of consumption that does not vary with income (C).
• Marginal propensity to consume (MPC): The change in planned consumption due to a change in disposable income (c).
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Consumption and Disposable Income
Source: Frank, Bernanke, Antonovics, and Heffetz, “Principles of Economics.”
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V. DETERMINATION OF OUTPUT IN THE SHORT RUN
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45-degree Line
• Captures the equilibrium condition that Y = PAE.
• Also reflects the empirical/behavioral reality that output responds to planned spending in the short run.
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45-degree Line
PAE
Y
Y=PAE
45°
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Expenditure Line
• Captures the fact that planned aggregate spending is a function of total income (which is the same as total output).
• PAE = C + Ip + G + NX, where C = f(Y−T).
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Expenditure Line
Y
C
PAE = C + Ip + G + NX PAE
The slope of the expenditure line (PAE) is the MPC.
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Determination of Output in the Short Run
• Output in the short run is determined by the intersection of the 45-degree line and the expenditure line.
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Determination of Short-Run Output
Y
PAE
PAE Y=PAE
Y1 Sometimes called the “Keynesian Cross” diagram.
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How does the economy get to short-run equilibrium?
Y
PAE
PAE Y=PAE
Y1 Y3 Y2
At Y2, unintended inventory investment leads firms to cut production.
At Y3, unintended negative inventory investment leads firms to increase production.
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Long-Run Equilibrium
Y
PAE
PAE Y=PAE
Y* In the long run, PAE=Y and PAE cross at Y* (potential output).
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VI. SHIFTS IN THE EXPENDITURE LINE
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Crucial Determinant of Short-Run Fluctuations: Shifts in the Expenditure Line
• Expenditure line (PAE) shows how planned spending varies with output.
• Anything that changes planned spending other than output, will shift the curve.
• If the expenditure line shifts, short-run equilibrium output will change.
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Example: A Fall in Autonomous Consumption
• A fall in consumption not caused by a fall in output.
• A decline in the intercept of the consumption function (C).
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Great Crash of the Stock Market in October 1929
Source: Federal Reserve Bank of St. Louis, FRED.
0
50
100
150
200
250
300
350
400
Dec-
14De
c-15
Dec-
16De
c-17
Dec-
18De
c-19
Dec-
20De
c-21
Dec-
22De
c-23
Dec-
24De
c-25
Dec-
26De
c-27
Dec-
28De
c-29
Dec-
30De
c-31
Dec-
32De
c-33
Dec-
34De
c-35
Dow
Jone
s Ind
ustr
ial A
vera
ge (I
ndex
)
September 1929
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Why Might a Fall in Stock Prices Reduce Consumer Spending (at a Given Level of
Output)?
• Reduction in wealth makes consumers feel poorer.
• Fall in stock prices makes consumers pessimistic (lowers consumer confidence).
• Stock price volatility causes uncertainty and leads to “wait and see” behavior.
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The Collapse of Consumer Spending in Late 1929
Source: Christina Romer, “The Great Crash and the Onset of the Great Depression.”
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A Fall in Autonomous Consumption
Y−T
C
C1
C1
C2
C2
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A Fall in Autonomous Consumption
Y
PAE1
PAE Y=PAE
Y*
PAE2
Y2
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Real GDP, 1909–1939
Source: Christina Romer, “The Prewar Business Cycle Reconsidered,” and BEA.
400
500
600
700
800
900
1000
1100
1200
1300
1909
1911
1913
1915
1917
1919
1921
1923
1925
1927
1929
1931
1933
1935
1937
1939
Real
GDP
in C
hain
ed 2
009
Dolla
rs
1929
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The Multiplier Effect
Y
PAE1
PAE Y=PAE
Y*
PAE2
Y2 The initial drop in PAE is magnified by the fact that as Y declines, C declines further.
Initial drop in PAE due to the drop in C
Decline in Y is larger because of the multiplier effect
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Multiplier Effect
• A change in PAE changes output by more than the initial change in PAE.
• Why? Because changes in output affect consumer spending and reinforce (or multiply) the initial change in PAE.
• Existence of the multiplier effect explains why moderate changes in planned spending cause more substantial changes in output.