# Aggregate Demand and Supply

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Aggregate Demand and Supply

The Aggregate Demand Curve
Aggregate demand is the total demand for goods and services in the economy.

Deriving the Aggregate Demand Curve
To derive the aggregate demand curve, we examine what happens to aggregate output (income) (Y) when the price level (P) changes, assuming no changes in government spending (G), net taxes (T), or the monetary policy variable (Ms).

Deriving the Aggregate Demand Curve
The Impact of an Increase in the Price Level on the Economy – Assuming No Changes in G, T, and Ms

Deriving the Aggregate Demand Curve
The aggregate demand (AD) curve is a curve that shows the negative relationship between aggregate output (income) and the price level.

The Aggregate Demand Curve: A Warning
The AD curve is not a market demand curve. It is a more complex concept. We cannot use the ceteris paribus assumption to draw an AD curve. In reality, many prices (including input prices) rise together.

The Aggregate Demand Curve: A Warning
A higher price level causes the demand for money to rise, which causes the interest rate to rise. Then, the higher interest rate causes aggregate output to fall.

The Aggregate Demand Curve: A Warning
At all points along the AD curve, both the goods market and the money market are in equilibrium.

Other Reasons for a Downward-Sloping Aggregate Demand Curve
The consumption link: The decrease in consumption brought about by an increase in the interest rate contributes to the overall decrease in output.

Other Reasons for a Downward-Sloping Aggregate Demand Curve
The real wealth effect, or real balance, effect is the change in consumption brought about by a change in real wealth that results from a change in the price level.

Aggregate Expenditure and Aggregate Demand
At every point along the aggregate demand curve, the aggregate quantity of output demanded is exactly equal to planned aggregate expenditure. Y = C + I + G equilibrium condition

Shifts of the Aggregate Demand Curve
An increase in the quantity of money supplied at a given price level shifts the aggregate demand curve to the right.

Shifts of the Aggregate Demand Curve
An increase in government purchases or a decrease in net taxes shifts the aggregate demand curve to the right.

Shifts of the Aggregate Demand Curve
Factors That Shift the Aggregate Demand Curve Expansionary monetary policy Ms AD curve shifts to the right Contractionary monetary policy Ms AD curve shifts to the left Expansionary fiscal policy G AD curve shifts to the right Contractionary fiscal policy G AD curve shifts to the left T AD curve shifts to the right T AD curve shifts to the left

The Aggregate Supply Curve
Aggregate supply is the total supply of all goods and services in the economy.

The Aggregate Supply Curve
The aggregate supply (AS) curve is 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
The aggregate supply curve is not a market supply curve or the sum of all the individual supply curves in the economy.

The Aggregate Supply Curve: A Warning
Firms do not simply respond to market-determined prices, but they actually set prices. Price-setting firms do not have individual supply curves because these firms are choosing both output and price at the same time.

The Aggregate Supply Curve: A Warning
When we draw a firm’s supply curve, we assume that input prices are constant. In macroeconomics, an increase in the overall price level means that at least some input prices will be rising as well. The outputs of some firms are the inputs of other firms.

The Aggregate Supply Curve: A Warning
Rather than an aggregate supply curve, what does exist is a “price/output response” curve — a curve that traces out the price and output decisions of all the markets and firms in the economy under a given set of circumstances.

Aggregate Supply in the Short Run
In the short run, the aggregate supply curve (the price/output response curve) has a positive slope. Firms may at time have excess capital and excess labor on hand. The reasons for this are associated with the costs of getting rid of capital and labor.

Aggregate Supply in the Short Run
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. Firms may at time have excess capital and excess labor on hand. The reasons for this are associated with the costs of getting rid of capital and labor.

Aggregate Supply in the Short Run
Macroeconomists focus on whether or not the economy as a whole is operating at full capacity. As the economy approaches maximum capacity, firms respond to further increases in demand only by raising prices.

Output Levels and Price/Output Responses
When the economy is operating at low levels of output, an increase in aggregate demand is likely to result in an increase in output with little or no increase in the overall price level.

The Response of Input Prices to Changes in the Overall Price Level
There must be a lag between changes in input prices and changes in output prices, otherwise the aggregate supply (price/output response) curve would be vertical. If input and output prices rise by the same percentage amount, no firm would find it advantageous to change its level of output.

The Response of Input Prices to Changes in the Overall Price Level
Wage rates may increase at exactly the same rate as the overall price level if the price-level increase is fully anticipated. Most input prices, however, tend to lag increases in output prices. If input and output prices rise by the same percentage amount, no firm would find it advantageous to change its level of output.

Shifts of the Short-Run Aggregate Supply Curve
A cost shock, or supply shock, is a change in costs that shifts the aggregate supply (AS) curve. Cost shocks refer to an increase in costs, which may be the result of an increase in wage rates, energy prices, natural disasters, economic stagnation, and the like.

Shifts of the Short-Run Aggregate Supply Curve
Bad weather, natural disasters, destruction from wars Good weather Public policy waste and inefficiency over-regulation Public policy supply-side policies tax cuts deregulation Stagnation capital deterioration Economic growth more capital more labor technological change Higher costs higher input prices higher wage rates Lower costs lower input prices lower wage rates Shifts to the Left Decreases in Aggregate Supply Shifts to the Right Increases in Aggregate Supply Factors That Shift the Aggregate Supply Curve

The Equilibrium Price Level
The equilibrium price level is the point at which the aggregate demand and aggregate supply curves intersect.

The Equilibrium Price Level
P0 and Y0 correspond to equilibrium in the goods market and the money market and a set of price/output decisions on the part of all the firms in the economy.

The Long-Run Aggregate Supply Curve
Costs lag behind price-level changes in the short run, resulting in an upward-sloping AS curve. Costs and the price level move in tandem in the long run, and the AS curve is vertical.

The Long-Run Aggregate Supply Curve
Output can be pushed above potential GDP by higher aggregate demand. The aggregate price level also rises.

The Long-Run Aggregate Supply Curve
When output is pushed above potential, there is upward pressure on costs, and this causes the short-run AS curve to the left. Costs ultimately increase by the same percentage as the price level, and the quantity supplied ends up back at Y0.

The Long-Run Aggregate Supply Curve
Y0 represents the level of output that can be sustained in the long run without inflation. It is also called potential output or potential GDP.

Aggregate Demand, Aggregate Supply, and Monetary and Fiscal Policy
AD 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. Expansionary policy works well when the economy is on the flat portion of the AS curve, causing little change in P relative to the output increase.

Aggregate Demand, Aggregate Supply, and Monetary and Fiscal Policy
On the steep portion of the AS curve, expansionary policy does not work well. The multiplier is close to zero. When the economy is operating near full capacity, an increase in AD will result in an increase in the price level with little increase in output.

Long-Run Aggregate Supply and Policy Effects
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 multiplier effect of a change in government spending or taxes on aggregate output is zero.

The Simple “Keynesian” Aggregate Supply Curve
The output of the economy cannot exceed the maximum output of YF. The difference between planned aggregate expenditure and aggregate output at full capacity is sometimes referred to as an inflationary gap.

Causes of Inflation Inflation is an increase in the overall price level. Sustained inflation occurs when the overall price level continues to rise over some fairly long period of time.

Causes of Inflation Demand-pull inflation is inflation initiated by an increase in aggregate demand. Cost-push, or supply-side, inflation is inflation caused by an increase in costs.

Cost-Push, or Supply-Side Inflation
Stagflation occurs when output is falling at the same time that prices are rising. One possible cause of stagflation is an increase in costs.

Cost-Push, or Supply-Side Inflation
Cost shocks are bad news for policy makers. The only way to counter the output loss is by having the price level increase even more than it would without the policy action.

Expectations and Inflation
If every firm expects every other firm to raise prices by 10%, every firm will raise prices by about 10%. This is how expectations can get “built into the system.” In terms of the AD/AS diagram, an increase in inflationary expectations shifts the AS curve to the left. If prices have been rising, and if people’s expectations are adaptive—that is, if they form their expectations on the basis of past pricing behavior—then firms may continue raising prices even if demand is slowing or contracting.

Money and Inflation Hyperinflation is a period of very rapid increases in the price level. If prices have been rising, and if people’s expectations are adaptive—that is, if they form their expectations on the basis of past pricing behavior—then firms may continue raising prices even if demand is slowing or contracting.

Money and Inflation An increase in G with the money supply constant shifts the AD curve from AD0 to AD1. This leads to an increase in the interest rate and crowding out of planned investment. If prices have been rising, and if people’s expectations are adaptive—that is, if they form their expectations on the basis of past pricing behavior—then firms may continue raising prices even if demand is slowing or contracting.

Money and Inflation If the Fed tries to prevent crowding, it will increase the money supply and the AD curve will shift farther and farther to the right. The result is a sustained inflation, perhaps hyperinflation. If prices have been rising, and if people’s expectations are adaptive—that is, if they form their expectations on the basis of past pricing behavior—then firms may continue raising prices even if demand is slowing or contracting.