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Aggregate
Demand

Understand how the total spending in an economy determines output, prices, and the shape of the AD curve.

AP Macroeconomics

What Is Aggregate Demand?

Aggregate Demand (AD) represents the total quantity of goods and services that all buyers in an economy are willing and able to purchase at each possible price level, during a specific time period.

The AD Equation

Aggregate Demand is the sum of spending by all sectors of the economy. The formula is:

\(C\)
Consumer spending: household purchases of goods and services
\(I\)
Investment: business spending on capital, inventories, and new construction
\(G\)
Government spending: federal, state, and local purchases
\(X - M\)
Net exports: exports minus imports (trade balance)

Why Does AD Matter?

Aggregate Demand is central to macroeconomics because changes in AD drive recessions, expansions, and inflation. Policymakers use fiscal and monetary tools to shift AD.

1
Short-run output: When AD rises, firms produce more and hire more workers.
2
Price level: An increase in AD can push prices higher, contributing to inflation.
3
Policy lever: Governments shift AD through spending/taxes; central banks shift AD through interest rates and money supply.

The AD Curve

Price Level (PL) Real GDP (Y) AD

Why AD Slopes Downward

Wealth Effect
A lower price level increases the real value of money, making consumers wealthier and increasing \(C\).
Interest-Rate Effect
Lower prices reduce the demand for money, lowering interest rates and boosting \(I\).
Exchange-Rate Effect
Lower interest rates weaken the domestic currency, making exports cheaper and increasing \(X - M\).

AD vs. Micro Demand

Aggregate Demand Micro Demand
Y-Axis Overall price level (GDP deflator / CPI) Price of one good
X-Axis Real GDP (total output) Quantity of one good
Why Downward? Wealth, interest-rate, exchange-rate effects Substitution and income effects
Scope Entire economy Single market

Shifting the AD Curve

A change in any component of \(AD = C + I + G + (X - M)\) that is not caused by a change in the price level will shift the entire AD curve.

PL Real GDP
\(AD_0\)
\(AD_1\)
\(AD_2\)

Key AD Shifters

1
Consumer confidence: Optimistic consumers spend more, shifting AD right.
2
Interest rates: Lower rates reduce borrowing costs, increasing \(I\) and \(C\).
3
Government policy: Higher \(G\) or tax cuts increase disposable income and spending.
4
Foreign income: Higher income abroad raises demand for our exports (\(X\) rises).
5
Exchange rates: A weaker domestic currency makes exports cheaper, boosting \(X - M\).

How to Analyze an AD Shift

1
Identify the event: Determine which component of \(C + I + G + (X - M)\) is affected.
2
Direction of change: Does the event increase or decrease that component?
3
Shift AD: Increase in a component shifts AD right; decrease shifts AD left.
4
New equilibrium: Find where the shifted AD meets the AS curve. Identify the new price level and real GDP.

Example: Tax Cut

Scenario: The government enacts a broad income tax cut. How does this affect aggregate demand?

1
Component affected: \(C\) (consumer spending) increases because households have higher disposable income.
2
Direction: \(C\) rises, so AD increases.
3
Shift: AD curve shifts to the right.
4
Result: Higher real GDP and a higher price level in the short run.

Example: Central Bank Raises Rates

Scenario: The central bank raises the federal funds rate to combat inflation.

PL Real GDP SRAS
\(AD_0\)
\(AD_1\)
\(Y_0\)
\(Y_1\)
\(PL_0\)
\(PL_1\)

Example: Foreign Recession

Scenario: A major trading partner enters a deep recession. How does this affect the domestic AD curve?

1
Component affected: \(X\) (exports) decreases because the foreign country buys fewer of our goods.
2
Net exports: \(X - M\) falls, reducing total spending.
3
Result: AD shifts left, leading to lower real GDP and a lower price level in the short run.

The Multiplier Effect

An initial change in spending creates a chain reaction. The spending multiplier amplifies the shift in AD.

If \(MPC = 0.8\)
\( \text{Multiplier} = \frac{1}{1 - 0.8} = 5 \). A \$100B increase in \(G\) shifts AD by \$500B.
If \(MPC = 0.6\)
\( \text{Multiplier} = \frac{1}{1 - 0.6} = 2.5 \). The same \$100B increase shifts AD by \$250B.

Common Mistakes

✕ Confusing Shift vs. Movement
A change in the price level causes movement along AD, not a shift. Only non-price-level factors shift AD.
✕ Using Micro Logic for AD
AD slopes down due to wealth, interest-rate, and exchange-rate effects: not substitution between goods.
✕ Ignoring the Multiplier
A \$50B increase in \(G\) does not shift AD by exactly \$50B. The multiplier amplifies the initial change.

Summary of AD Shifters

Factor AD Shifts Right AD Shifts Left
Consumer Confidence Increases Decreases
Interest Rates Fall Rise
Government Spending Increases Decreases
Taxes Cut Raised
Foreign Income Rises Falls
Domestic Currency Value Depreciates Appreciates

Question 1 of 5

Which of the following best explains why the aggregate demand curve slopes downward?

Question 2 of 5

If the marginal propensity to consume is \(MPC = 0.75\), what is the value of the spending multiplier?

Question 3 of 5

The government increases spending by \$80 billion. If the \(MPC = 0.8\), what is the total change in aggregate demand?

Question 4 of 5

Which of the following would cause the AD curve to shift to the left?

Question 5 of 5

A student claims: "When the price level rises, AD decreases, so the AD curve shifts left." What is wrong with this reasoning?