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11The Aggregate Supply CurveThe Aggregate Supply Curve: A WarningAggregate Supply in the Short RunShifts of the Short-Run Aggregate Supply Curve

The Equilibrium Price Level

The Long-Run Aggregate Supply CurvePotential GDP

Monetary and FiscalPolicy EffectsLong-Run Aggregate Supply and Policy Effects

Causes of InflationDemand-Pull InflationCost-Push, or Supply-Side, InflationExpectations and InflationMoney and InflationSustained Inflation as a Purely Monetary

Phenomenon

The Behavior of the Central BankControlling the Interest RateThe Central Bank’s Response to the State of the

EconomyThe central Bank Behavior Since 1970Inflation Targeting

LECTURE OUTLINE

Aggregate Supplyand the Equilibrium

Price Level

Lecture 9

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The Aggregate Supply Curve

aggregate supply The total supply of all goods and services in an economy.

aggregate supply (AS) curve A graph that shows the relationship between the aggregate quantity of output supplied by all firms in an economy and the overall price level.

The Aggregate Supply Curve: A Warning

An “aggregate supply curve” in the traditional sense of the word supply does not exist. What does exist is what we might call a “price/output response” curve—a curve that traces out the price decisions and output decisions of all firms in the economy under a given set of circumstances.

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The Aggregate Supply CurveAggregate Supply in the Short Run

In the short run, the aggregate supply curve (the price/output response curve) has a positive slope.At low levels of aggregate output, the curve is fairly flat.As the economy approaches capacity, the curve becomes nearly vertical.At capacity, the curve is vertical.

FIGURE 13.1 The Short-Run Aggregate Supply Curve

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The Aggregate Supply CurveShifts of the Short-Run Aggregate Supply Curve

cost shock, or supply shock A change in costs that shifts the short-run aggregate supply (AS) curve.

FIGURE 13.2 Shifts of the Short-Run Aggregate Supply Curve

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The Equilibrium Price Level

equilibrium price level The price level at which the aggregate demand and aggregate supply curves intersect.

At each point along the AD curve, both the money market and the goods market are in equilibrium. Each point on the AS curve represents the price/ output decisions of all the firms in the economy. P0 and Y0 correspond to equilibrium in the goods market and the money market and to a set of price/output decisions on the part of all the firms in the economy.

FIGURE 13.3 The Equilibrium Price Level

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The Long-Run Aggregate Supply Curve

When the AD curve shifts from AD0 to AD1, the equilibrium price level initially rises from P0 to P1 and output rises from Y0 to Y1.

Wages respond in the longer run, shifting the AS curve from AS0 to AS1.

If wages fully adjust, output will be back at Y0. Y0 is sometimes called potential GDP.

FIGURE 13.4 The Long-Run Aggregate Supply Curve

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The Long-Run Aggregate Supply Curve

The Simple “Keynesian” Aggregate Supply Curve

One view of the aggregate supply curve, the simple “Keynesian” view, holds that at any given moment, the economy has a clearly defined capacity, or maximum, output.

With planned aggregate expenditure of AE1

and aggregate demand of AD1, equilibrium output is Y1.

A shift of planned aggregate expenditure to AE2, corresponding to a shift of the AD curve to AD2, causes output to rise but the price level to remain at P1.

If planned aggregate expenditure and aggregate demand exceed YF, however, there is an inflationary gap and the price level rises to P3.

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The Long-Run Aggregate Supply CurvePotential GDP

potential output, or potential GDP The level of aggregate output that can be sustained in the long run without inflation.

Short-Run Equilibrium Below Potential Output

Although different economists have different opinions on how to determine whether an economy is operating at or above potential output, there is general agreement that there is a maximum level of output (below the vertical portion of the short-run aggregate supply curve) that can be sustained without inflation.

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Monetary and Fiscal Policy Effects

Aggregate demand can shift to the right for a number of reasons, including an increase in the money supply, a tax cut, or an increase in government spending. If the shift occurs when the economy is on the nearly flat portion of the AS curve, the result will be an increase in output with little increase in the price level from point A to point A’.

FIGURE 13.5 A Shift of the Aggregate Demand Curve When the Economy Is on the Nearly Flat Part of the AS Curve

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Monetary and Fiscal Policy Effects

If a shift of aggregate demand occurs while the economy is operating near full capacity, the result will be an increase in the price level with little increase in output from point B to point B’.

FIGURE 13.6 A Shift of the Aggregate Demand Curve When the Economy Is Operating at or Near Maximum Capacity

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Monetary and Fiscal Policy EffectsLong-Run Aggregate Supply and Policy Effects

It is important to realize that if the AS curve is vertical in the long run, neither monetary policy nor fiscal policy has any effect on aggregate output in the long run.

The conclusion that policy has no effect on aggregate output in the long run is perhaps startling.

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Causes of InflationDemand-Pull Inflation

demand-pull inflation Inflation that is initiated by an increase in aggregate demand.

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Causes of InflationCost-Push, or Supply-Side, Inflation

An increase in costs shifts the AS curve to the left. By assuming the government does not react to this shift, the AD curve does not shift, the price level rises, and output falls.

FIGURE 13.7 Cost-Push, or Supply-Side, Inflation

cost-push, or supply-side, inflation Inflation caused by an increase in costs.

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Causes of InflationCost-Push, or Supply-Side, Inflation

A cost shock with no change in monetary or fiscal policy would shift the aggregate supply curve from AS0 to AS1, lower output from Y0 to Y1, and raise the price level from P0 to P1.

Monetary or fiscal policy could be changed enough to have the AD curve shift from AD0 to AD1.

This policy would raise aggregate output Y again, but it would raise the price level further, to P2.

FIGURE 13.8 Cost Shocks Are Bad News for Policy Makers

stagflation Occurs when output is falling at the same time that prices are rising.

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Causes of InflationExpectations and Inflation

When firms are making their price/output decisions, their expectations of future prices may affect their current decisions. If a firm expects that its competitors will raise their prices, in anticipation, it may raise its own price.

Given the importance of expectations in inflation, the central banks of many countries survey consumers about their expectations.

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Causes of InflationMoney and Inflation

An increase in G with the money supply constant shifts the AD curve from AD0 to AD1. Although not shown in the figure, this leads to an increase in the interest rate and crowding out of planned investment. If the Central Bank tries to keep the interest rate unchanged by increasing the money supply, the AD curve will shift farther and farther to the right. The result is a sustained inflation, perhaps even hyperinflation.

FIGURE 13.9 Sustained Inflation From an Initial Increase in G and Fed Accommodation

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Causes of InflationSustained Inflation as a Purely Monetary Phenomenon

Virtually all economists agree that an increase in the price level can be caused by anything that causes the AD curve to shift to the right or the AS curve to shift to the left.

It is also generally agreed that for a sustained inflation to occur, the Central Bank must accommodate it.

In this sense, a sustained inflation can be thought of as a purely monetary phenomenon.

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The Behavior of the Central BankControlling the Interest Rate

The buying and selling of government securities by the Central Bank has two effects at the same time: It changes the money supply, and it changes the interest rate.

How much the interest rate changes depends on the shape of the money demand curve. The steeper the money demand curve, the larger the change in the interest rate for a given size change in government securities.

If the Central Bank wants to achieve a particular value of the money supply, it must accept whatever interest rate value is implied by this choice. Conversely, if the Central Bank wants to achieve a particular value of the interest rate, it must accept whatever money supply value is implied by this.

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The Behavior of the Central BankThe Fed’s Response to the State of the Economy

During periods of low output/low inflation, the economy is on the relatively flat portion of the AS curve. In this case, the Central Bank is likely to lower the interest rate (and thus expand the money supply). This will shift the AD curve to the right, from AD0 to AD1, and lead to an increase in output with very little increase in the price level.

FIGURE 13.11 The Central Bank’s Response to Low Output/Low Inflation

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The Behavior of the the Central BankThe Central Bank’s Response to the State of the Economy

During periods of high output/high inflation, the economy is on the relatively steep portion of the AS curve. In this case, the the Central Bank is likely to increase the interest rate (and thus contract the money supply).This will shift the AD curve to the left, from AD0 to AD1, and lead to a decrease in the price level with very little decrease in output.

FIGURE 13.12 The Central Bank’s Response to High Output/High Inflation

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The Behavior of the Central BankInflation Targeting

inflation targeting When a monetary authority chooses its interest rate values with the aim of keeping the inflation rate within some specified band over some specified horizon.

Rising Food Prices Worry Central Banks Around the World

Food Prices Worry Central Bankers

Wall Street Journal