Aggregate Expenditure & Output in the Short Run

Introduction to the Aggregate Expenditure Model

The Aggregate Expenditure (AE) model is a foundational macroeconomic model that examines the short-run relationship between total spending in the economy and the resulting level of output (real GDP) and employment. This model is crucial for understanding how fluctuations in spending can lead to changes in economic activity over short periods.

• Key Idea: In any given year, the level of GDP is determined by the level of aggregate expenditure (total spending).

• Short-run changes in real GDP and employment are primarily driven by changes in aggregate expenditure.

How the Aggregate Expenditure Model Works

The AE model explains how the relationship between total spending and total production determines changes in output and employment. The model focuses on the role of inventories as a signal for firms to adjust production.

• If total spending < total production (real GDP): Inventories increase, leading firms to decrease production and employment.

• If total spending > total production (real GDP): Inventories decrease, prompting firms to increase production and employment.

Scope and Assumptions of the AE Model

The AE model is designed to explain short-run fluctuations in output and employment, not long-term economic growth or inflation. It assumes that potential GDP and prices are fixed in the short run, making it a model for analyzing business cycles and cyclical unemployment.

• Not for long-term economic growth or inflation analysis.

• Assumes potential GDP is fixed and prices are constant.

• Focuses on short-run business cycles and cyclical unemployment.

Major Points of the Aggregate Expenditure Model

1. Total spending (AE) determines the level of real GDP (Y) in the short run.

2. Macroeconomic equilibrium occurs where planned AE equals total production (real GDP).

3. Unintended changes in inventories (real GDP – AE) signal whether firms should increase or decrease production and employment.

4. Consumption spending depends on: current disposable income (+), household wealth (+), expected future income (+), and the interest rate (–).

5. Marginal Propensity to Consume (MPC): Measures the change in consumption from a change in income:

6. Investment spending depends on: expectations of future profitability (+), the interest rate (–), and business taxes (–).

7. Net exports depend on: foreign real GDP (+) and the exchange rate between the dollar and other currencies (–).

Components of Aggregate Expenditure

Consumption Spending (C)

Consumption is the largest component of aggregate expenditure and is influenced by several key factors:

• Current Disposable Income: Higher disposable income increases consumption.

• Household Wealth: Increases in wealth (e.g., rising stock or housing prices) boost consumption.

• Expected Future Income: If households expect higher future income, they are likely to spend more today.

• Interest Rate: Higher interest rates encourage saving and make borrowing more expensive, reducing consumption, especially of durable goods.

Investment Spending (I)

Investment includes spending by firms on capital goods and by households on new homes. It is determined by:

• Expectations of Future Profitability: Optimism about future profits increases investment.

• Interest Rate: Higher interest rates make borrowing more expensive, reducing investment spending.

• Business Taxes: Higher corporate income taxes reduce after-tax profitability and investment, while investment tax credits encourage investment.

Government Purchases (G)

Government purchases include all spending by federal, state, and local governments on goods and services. This component is determined by government policy decisions and is not directly influenced by income or interest rates in the short run.

Net Exports (NX)

Net exports are the value of exports minus imports. Two main factors influence net exports:

• Growth Rate of GDP in the U.S. Relative to Other Countries: Higher foreign real GDP increases demand for U.S. exports, raising net exports.

• Exchange Rate between the Dollar and Other Currencies: An appreciation of the dollar makes U.S. exports more expensive and imports cheaper, reducing net exports.

Summary Table: Factors Affecting Components of Aggregate Expenditure

Key Equations

• Marginal Propensity to Consume (MPC):

• Aggregate Expenditure (AE):

• Macroeconomic Equilibrium: (where Y is real GDP)

Additional info: The AE model is a short-run model and does not account for price level changes or long-term growth. It is most useful for analyzing business cycles and the effects of shocks to spending on output and employment.