MACROECONOMICS
cover art ROW 1 (90)
C H A P T E R
© 2008 Worth Publishers, all rights reserved
SIXTH EDITION
PowerPoint® Slides by Ron Cronovich
N. GREGORY MANKIW
Aggregate Supply and the Short-run Tradeoff Between Inflation and Unemployment
13

Chapter 13 has two parts.  The first concerns aggregate supply.  In the preceding chapters, we made
the simple and extreme assumption that all prices were “stuck” in the short run.  This assumption
implied a horizontal short-run aggregate supply curve.  More realistic models of aggregate supply
imply an upward-sloping SRAS curve.  Chapter 13 presents three of the most prominent models.
The second half of the chapter is devoted to the Phillips curve and related issues.  The section
uses a few lines of algebra to derives an expression for the Phillips curve from the SRAS
equation.  This is followed by a discussion of adaptive and rational expectations, and the
sacrifice ratio.  The chapter concludes by contrasting the notion of hysteresis to the natural rate
hypothesis.
To help your students master the material, it would be helpful to assign homework or in-class
exercises in which students use the models to analyze the effects of policies and shocks.  Right
before the introduction of the Phillips curve would be a good place to have students work an
exercise using the
IS-LM-AD-AS model with a postively-sloped SRAS curve.  The key difference is that, in the short
run, a shift in AD causes P to change, which changes M/P, which shifts LM a bit, which explains why
the short-run change in output is smaller when SRAS is upward-sloping than when it is horizontal.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
In this chapter, you will learn…
§three models of aggregate supply in which output depends positively on the price level in the
short run
§about the short-run tradeoff between inflation and unemployment known as the Phillips curve
§

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
Three models of aggregate supply
1.The sticky-wage model
2.The imperfect-information model
3.The sticky-price model
§All three models imply:
natural rate of output
a positive parameter
the expected price level
the actual price level
agg.
output

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The sticky-wage model
§Assumes that firms and workers negotiate contracts and fix the nominal wage before they know what
the price level will turn out to be.
§The nominal wage they set is the product of a target real wage and the expected price level:
Target real wage

At the target real wage, the labor market is in equilibrium, meaning that unemployment equals its
natural rate.  This implies that output equals its natural rate (aka full-employment output).

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The sticky-wage model
§If it turns out that
then
Unemployment and output are at their natural rates.
Real wage is less than its target, so firms hire more workers and output rises above its natural
rate.
Real wage exceeds its target,
so firms hire fewer workers and output falls below its natural rate.

Intuition for the positive relationship between P and Y, for a given value of the expected price
level.

Mankiw6e_FIG
CHAPTER 13   Aggregate Supply
slide 5

I’ve included Figure 13-1 from the text here as a “hidden slide” in case you wish to “unhide” and
include it in your presentation.  This figure uses graphs to derive the aggregate supply curve
under the assumption of sticky wages.
As you can see, three-panel diagrams do not translate well to the big screen.  Fortunately, though,
most students readily grasp the intuition on the preceding slide, which sums up as follows:
If the nominal wage is fixed, then increases in the price level cause the real wage to fall, which
causes firms to hire more workers and produce more output.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The sticky-wage model
§Implies that the real wage should be
counter-cyclical, should move in the opposite direction as output during business cycles:
§In booms, when P  typically rises,
real wage should fall.
§In recessions, when P  typically falls,
real wage should rise.
§This prediction does not come true in the real world:

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The cyclical behavior of the real wage
Percentage change in real GDP
-5
-4
-3
-2
-1
0
1
2
3
4
5
-3
-2
-1
0
1
2
3
4
5
6
7
8
1974
1979
1991
1972
2004
2001
1998
1965
1984
1980
1982
1990

Figure 13-2, p.380
The real wage is procyclical in the U.S., contrary to the sticky wage theory.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The imperfect-information model
§Assumptions:
§All wages and prices are perfectly flexible,
all markets are clear.
§Each supplier produces one good, consumes many goods.
§Each supplier knows the nominal price of the good she produces, but does not know the overall
price level.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The imperfect-information model
§Supply of each good depends on its relative price:  the nominal price of the good divided by the
overall price level.
§Supplier does not know price level at the time she makes her production decision, so uses the
expected price level, P e.
§Suppose P  rises but P e does not.
§Supplier thinks her relative price has risen,
so she produces more.
§With many producers thinking this way,
Y will rise whenever P rises above P e.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The sticky-price model
§Reasons for sticky prices:
§long-term contracts between firms and customers
§menu costs
§firms not wishing to annoy customers with frequent price changes
§Assumption:
§Firms set their own prices
(e.g., as in monopolistic competition).

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If you don’t like the appearance of the term “monopolistic competition” in this slide, just change
the parenthetical comment to “(i.e. firms have some market power)” or something to that effect.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The sticky-price model
§An individual firm’s desired price is
where  a > 0.
Suppose two types of firms:
•firms with flexible prices, set prices as above
•firms with sticky prices, must set their price before they know how P  and Y  will turn out:

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The sticky-price model
§Assume sticky price firms expect that output will equal its natural rate.  Then,
§To derive the aggregate supply curve, we first find an expression for the overall price level.
§Let s  denote the fraction of firms with sticky prices.  Then, we can write the overall price
level as…

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The sticky-price model
§Subtract (1-s )P  from both sides:
price set by flexible price firms
price set by sticky price firms
§Divide both sides by s :

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The sticky-price model
§High P e  High P
If firms expect high prices, then firms that must set prices in advance will set them high.
Other firms respond by setting high prices.
§High Y   High P
When income is high, the demand for goods is high.  Firms with flexible prices set high prices.
§ The greater the fraction of flexible price firms,
the smaller is s  and the bigger is the effect
of  Y  on  P.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The sticky-price model
§Finally, derive AS equation by solving for Y :

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The sticky-price model
§In contrast to the sticky-wage model, the sticky-price model implies a pro-cyclical real wage:
§ Suppose aggregate output/income falls.  Then,
§Firms see a fall in demand for their products.
§Firms with sticky prices reduce production, and hence reduce their demand for labor.
§The leftward shift in labor demand causes
the real wage to fall.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
Summary & implications
§Each of the
three models of agg. supply imply the relationship summarized by the SRAS curve & equation.
Y
P
LRAS
SRAS

The following is not in the text, but you and your students may find it worthwhile:
There are good reasons to believe that the SRAS curve is bow-shaped in the real world; that is, the
curve is steeper at high levels of output than at low levels of output.  And there are good reasons
why we should care about this.
Why the SRAS curve is bow-shaped:
At low levels of output, there are lots of unutilized and under-utilized resources available, so it
is not terribly costly for firms to increase output, and therefore firms do not require a big
increase in prices to make them willing to increase output by a given amount.  In contrast, at very
high levels of output, when unemployment is below the natural rate and capital is being used at
higher than normal intensity levels, it is relatively costly for firms to increase output further.
Hence, a larger increase in prices is required to make firms willing to increase their output.
Why the curvature matters:
When policymakers increase aggregate demand, output rises (good) and prices rise (not good).  An
important question arises:  how much of the bad thing (price increases) must we tolerate to get
some of the good thing (an increase output)?   The answer depends on how steep the SRAS curve is.
When President Reagan cut taxes in the early 1980s, the economy was just coming out of a severe
recession, and was on the flatter part of the SRAS curve; hence, the tax cuts affected output a lot
and inflation very little.  In contrast, when the current President Bush proposed huge tax cuts
during the 2000 election season, we were on the steeper part of the SRAS curve, so the tax cuts
would likely have been inflationary.  Of course, by the time they were implemented, the economy was
in recession, and in any case the bulk of the tax cuts were to be spread out over 10 or 11 years,
so they have not proved inflationary.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
Summary & implications
§Suppose a positive AD shock moves output above its natural rate and
P above the level people had expected.
Y
P
LRAS
SRAS1
SRAS equation:
AD1
AD2
Over time,
P e rises,
SRAS shifts up,
and output returns
to its natural rate.
SRAS2

This graph has two lessons for students:
First, changes in the expected price level shift the SRAS curve (this should be clear from the
equation, as should the fact that a change in the natural rate of output will shift the SRAS
curve).
The second lesson concerns the adjustment of the economy back to full-employment output.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
Inflation, Unemployment,
and the Phillips Curve
§The Phillips curve states that p  depends on
§expected inflation, p e.
§cyclical unemployment:  the deviation of the actual rate of unemployment from the natural rate
§supply shocks, n  (Greek letter “nu”).
where b > 0 is an exogenous constant.

  measures the responsiveness of inflation to cyclical unemployment.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
Deriving the Phillips Curve from SRAS

Explain each equation briefly before displaying the next.  Here are the explanations:
§Equation (1)  is the SRAS equation.
§Solve (1) for P to get (2).
§To get (3), add the supply shock term to (2).
§To get (4), subtract last year’s price level (P[-1]) from both sides.
§To get (5), write  in place of (P- P[-1])  and  ^e  in place of (P^e- P[-1]).  Note that the
change in the price level is not exactly the inflation rate, unless we interpret P as the natural
log of the price level.
§Equation (6) captures the relationship between output and unemployment from Okun’s law (chapter
2):  the deviation of output from its natural rate is inversely related to cyclical unemployment.
§Substituting (6) into (5) gives (7), the Phillips curve equation introduced on the preceding
slide.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The Phillips Curve and SRAS
§SRAS  curve:
Output is related to
unexpected movements in the price level.
§Phillips curve:
Unemployment is related to
unexpected movements in the inflation rate.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
Adaptive expectations
§Adaptive expectations:  an approach that assumes people form their expectations of future
inflation based on recently observed inflation.
§A simple example:
Expected inflation = last year’s actual inflation
§Then, the P.C. becomes

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
Inflation inertia
§In this form, the Phillips curve implies that inflation has inertia:
§In the absence of supply shocks or cyclical unemployment, inflation will continue indefinitely at
its current rate.
§Past inflation influences expectations of current inflation, which in turn influences the wages &
prices that people set.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
Two causes of rising & falling inflation
§cost-push inflation:
inflation resulting from supply shocks
§ Adverse supply shocks typically raise production costs and induce firms to raise prices,
“pushing” inflation up.
§demand-pull inflation:
inflation resulting from demand shocks
§ Positive shocks to aggregate demand cause unemployment to fall below its natural rate,
which “pulls” the inflation rate up.

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Of course, a favorable supply shock that lowers production costs will “push” inflation down, and a
negative demand shock which raises cyclical unemployment will “pull” inflation down.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
Graphing the Phillips curve
§In the short
run, policymakers face a tradeoff between p and u.
 u
p
The short-run Phillips curve

Here, the “short run” is the period until people adjust their expectations of inflation.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
Shifting the Phillips curve
§People adjust their expectations over time,
so the tradeoff only holds in the short run.
 u
p
E.g., an increase
in pe  shifts the short-run P.C. upward.

After displaying this slide, you might consider giving your students an exercise using the P.C.
curve.  One possibility would be to ask them to draw a graph of the PC curve, then show what
happens to it in the face of an adverse supply shock or an increase in the natural rate of
unemployment, giving intuition for each.
The intuition for why an increase in the natural rate shifts the PC upward (or rightward) is as
follows:
At any given value of actual unemployment, an increase in the natural rate implies a decrease in
cyclical unemployment, which increases inflation by increasing pressures for wages to rise.  Thus,
each value of unemployment has a higher value of inflation than before.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The sacrifice ratio
§To reduce inflation, policymakers can
contract agg. demand, causing
unemployment to rise above the natural rate.
§The sacrifice ratio measures
the percentage of a year’s real GDP
that must be foregone to reduce inflation
by 1 percentage point.
§A typical estimate of the ratio is 5.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The sacrifice ratio
§Example:  To reduce inflation from 6 to 2 percent, must sacrifice 20 percent of one year’s GDP:
§GDP loss =  (inflation reduction) x (sacrifice ratio)
  =                4                x           5
§This loss could be incurred in one year or spread over several, e.g., 5% loss for each of four
years.
§The cost of disinflation is lost GDP.
One could use Okun’s law to translate this cost into unemployment.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
Rational expectations
§Ways of modeling the formation of expectations:
§adaptive expectations:
People base their expectations of future inflation on recently observed inflation.
§rational expectations:
People base their expectations on all available information, including information about current
and prospective future policies.

A good example to illustrate the difference between adaptive and rational expectations.
Suppose the Fed announces a shift in priorities, from maintaining low inflation to maintaining low
unemployment w/o regard to inflation; this shift will start affecting policy next week.
If expectations are adaptive, then expected inflation will not change, because it is based on past
inflation.  The Fed’s announcement pertains to the future, and has no impact on past inflation.
If expectations are rational, then expected inflation will increase right away, as people factor
this announcement into their forecasts.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
Painless disinflation?
§Proponents of rational expectations believe
that the sacrifice ratio may be very small:
§Suppose  u = u n  and  p = pe = 6%,
§ and suppose the Fed announces that it will
do whatever is necessary to reduce inflation
from 6 to 2 percent as soon as possible.
§If the announcement is credible,
then pe will fall, perhaps by the full 4 points.
§Then, p can fall without an increase in u.

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Here’s an interesting and important implication:
Central banks that are politically independent are typically more credible than those that are
“puppets” to elected officials.  Hence, in countries with central banks that are NOT politically
independent, it is usually far costlier to reduce inflation.  A very worthwhile reform, therefore,
would be for governments to give their central banks independence.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
Calculating the sacrifice ratio
for the Volcker disinflation
§1981:  p = 9.7%
§ 1985:  p = 3.0%
year
u
u n
u-u n
1982
9.5%
6.0%
3.5%
1983
9.5
6.0
3.5
1984
7.4
6.0
1.4
1985
7.1
6.0
1.1
Total  9.5%
Total disinflation = 6.7%

The natural rate of unemployment is assumed to be 6.0% during the early 1980s.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
Calculating the sacrifice ratio
for the Volcker disinflation
§From previous slide:  Inflation fell by 6.7%,
total cyclical unemployment was 9.5%.
§Okun’s law:
1% of unemployment = 2% of lost output.
§So, 9.5% cyclical unemployment
= 19.0% of a year’s real GDP.
§Sacrifice ratio = (lost GDP)/(total disinflation)
§ = 19/6.7 = 2.8 percentage points of GDP were lost for each 1 percentage point reduction in
inflation.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
The natural rate hypothesis
§Our analysis of the costs of disinflation, and of economic fluctuations in the preceding chapters,
is based on the natural rate hypothesis:
Changes in aggregate demand affect output
and employment only in the short run.
In the long run, the economy returns to
the levels of output, employment,
and unemployment described by
the classical model (Chaps. 3-8).

The natural rate hypothesis allows us to study the long run separately from the short run.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
An alternative hypothesis:  Hysteresis
§Hysteresis:  the long-lasting influence of history on variables such as the natural rate of
unemployment.
§Negative shocks may increase un,
so economy may not fully recover.

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CHAPTER 13   Aggregate Supply
CHAPTER 13   Aggregate Supply
Hysteresis:  Why negative shocks may increase the natural rate
§The skills of cyclically unemployed workers may deteriorate while unemployed, and they may not
find a job when the recession ends.
§Cyclically unemployed workers may lose
their influence on wage-setting;
then, insiders (employed workers)
may bargain for higher wages for themselves.
§ Result:  The cyclically unemployed “outsiders”
may become structurally unemployed when the recession ends.

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Chapter Summary
§1. Three models of aggregate supply in the short run:
§sticky-wage model
§imperfect-information model
§sticky-price model
§ All three models imply that output rises above its natural rate when the price level rises above
the expected price level.
§
CHAPTER 13   Aggregate Supply
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Chapter Summary
§2. Phillips curve
§derived from the SRAS curve
§states that inflation depends on
§expected inflation
§cyclical unemployment
§supply shocks
§presents policymakers with a short-run tradeoff between inflation and unemployment
CHAPTER 13   Aggregate Supply
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Chapter Summary
§3. How people form expectations of inflation
§adaptive expectations
§based on recently observed inflation
§implies “inertia”
§rational expectations
§based on all available information
§implies that disinflation may be painless
§
CHAPTER 13   Aggregate Supply
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Chapter Summary
§4. The natural rate hypothesis and hysteresis
§the natural rate hypotheses
§states that changes in aggregate demand can only affect output and employment in the short run
§hysteresis
§states that aggregate demand can have permanent effects on output and employment
CHAPTER 13   Aggregate Supply
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