The AD-AS model explains how the overall price level and real GDP are determined in the macroeconomy. AP Macroeconomics students use this model to analyze recessions, inflation, supply shocks, and stabilization policy. This cheat sheet helps organize the curves, shifts, equilibrium outcomes, and policy tools that appear often on graphs and free-response questions.
Aggregate demand shows total spending, short-run aggregate supply shows production at different price levels, and long-run aggregate supply marks potential output. Changes in spending, input costs, productivity, taxes, government purchases, and money supply shift the curves. The most important skills are identifying the shock, drawing the correct shift, naming the output gap, and choosing the appropriate fiscal or monetary policy response.
Key Facts
- Macroeconomic equilibrium occurs where AD intersects SRAS, determining the short-run price level and real GDP.
- Long-run equilibrium occurs when AD, SRAS, and LRAS intersect at the same real GDP level, so actual output equals potential output.
- AD = C + I + G + Xn, where C is consumption, I is investment, G is government purchases, and Xn is net exports.
- An increase in AD raises the price level and real GDP in the short run, while a decrease in AD lowers the price level and real GDP in the short run.
- A negative supply shock shifts SRAS left, causing higher inflation and lower real GDP, which is called stagflation.
- A recessionary gap occurs when real GDP is less than potential GDP, so unemployment is above the natural rate.
- An inflationary gap occurs when real GDP is greater than potential GDP, so unemployment is below the natural rate.
- Expansionary policy increases AD, while contractionary policy decreases AD to reduce inflationary pressure.
Vocabulary
- Aggregate Demand
- Aggregate demand is the total quantity of goods and services demanded at each price level in an economy.
- Short-Run Aggregate Supply
- Short-run aggregate supply is the total quantity of goods and services firms are willing to produce at each price level when some input prices are sticky.
- Long-Run Aggregate Supply
- Long-run aggregate supply is the level of real GDP an economy can produce when resources are fully employed.
- Recessionary Gap
- A recessionary gap occurs when actual real GDP is below potential real GDP.
- Inflationary Gap
- An inflationary gap occurs when actual real GDP is above potential real GDP.
- Stabilization Policy
- Stabilization policy is the use of fiscal or monetary tools to move the economy closer to full employment output.
Common Mistakes to Avoid
- Shifting AD when only the price level changes is wrong because movement along AD happens when the price level changes, while AD shifts when a spending component changes.
- Confusing SRAS and LRAS is wrong because SRAS can slope upward in the short run, while LRAS is vertical at potential real GDP.
- Using expansionary policy during an inflationary gap is wrong because expansionary policy increases AD and can make demand-pull inflation worse.
- Ignoring the price level effect of supply shocks is wrong because a leftward SRAS shift raises the price level while lowering real GDP.
- Labeling every recession as a supply problem is wrong because many recessions are caused by falling AD, which lowers both real GDP and the price level.
Practice Questions
- 1 If AD shifts right from real GDP 18 trillion to 19 trillion while potential GDP is 18 trillion, what type of output gap occurs?
- 2 Suppose government spending increases by 200 billion and the spending multiplier is 4. What is the expected change in aggregate demand?
- 3 If oil prices rise sharply, which curve shifts, in what direction, and what happens to the price level and real GDP in the short run?
- 4 Explain why a central bank might choose contractionary monetary policy even if higher interest rates could slow real GDP growth.
Understanding AP Macroeconomics AD-AS Model and Policy
The downward slope of aggregate demand comes from several spending effects. When the overall price level rises, households and firms need more money for ordinary purchases. Interest rates tend to rise when people demand more money, so borrowing for homes, cars, factories, and equipment becomes less attractive.
Higher domestic prices can make exports less competitive while imported goods look cheaper. Real wealth matters too.
If the prices of goods rise while savings and fixed incomes do not, people can afford fewer goods. These effects reduce planned spending as the price level rises.
Short run aggregate supply slopes upward because many production costs do not change immediately. Wages are often set by contracts. Businesses may have fixed prices for supplies or rent.
When firms receive higher prices for what they sell, producing more can be profitable before all their costs catch up. Over time, workers and firms adjust their expectations. If they expect a permanently higher price level, workers seek higher wages and firms face higher costs.
Short run aggregate supply then shifts until output returns to the economy’s sustainable level. Long run aggregate supply depends on real productive capacity, including labor, physical capital, natural resources, and technology. A change in the price level alone does not create more factories, trained workers, or productive machines.
Fiscal policy works through the federal budget. More government purchases directly raise total spending because the government buys goods or services. A tax cut can raise household disposable income, though households may save part of the extra income.
The first increase in spending can lead to further rounds of spending, called the multiplier process. Its size is limited when households save, pay taxes, or buy imports. Fiscal policy can be slow because laws must pass through the political process.
It can also crowd out some private investment if government borrowing pushes interest rates upward. Students should distinguish a change in government purchases from a transfer payment. A transfer payment may affect spending, but it is not itself a purchase of current output.
Monetary policy begins with the central bank changing financial conditions. When it lowers its target interest rate and makes reserves more available, banks can lend more easily. Lower borrowing costs encourage interest sensitive spending, especially business investment and housing.
The reverse process can cool excessive spending. Monetary policy has time lags because firms do not build a new plant the moment rates fall. It may be weak during severe downturns if businesses expect low sales and avoid borrowing.
On graphs and exam responses, trace every event in order. Name the initial shock, identify the curve that shifts, compare short run output with potential output, then state the policy direction.
Be precise about the tradeoff after a supply shock. Reducing inflation can worsen unemployment, while supporting output can add inflation pressure.