The aggregate demand curve

Aggregate demand represents the total amount of goods and services that all groups in an economy want to buy at different price levels.

Characteristics of the AD curve

The AD curve shows the relationship between the overall price level in the economy and the total output demanded. It slopes downwards from left to right, meaning that as the price level falls, the quantity of output demanded rises.

Key features of the AD curve:

• Axes - The x-axis shows national output, while the y-axis shows the price level (often measured using the Consumer Price Index).
• Downward slope - Lower prices increase the purchasing power of money, allowing consumers to buy more goods and services, which boosts demand for output.

Movements along the AD curve

A movement along the AD curve happens when there is a change in the price level, leading to a change in the quantity of output demanded, without shifting the curve itself.

Reasons for movements along the curve

Rise in price level:

• Domestic buyers find goods and services more expensive, reducing consumption.
• Exports become less competitive as domestically produced items cost more for foreign buyers.
• Imports appear cheaper if foreign prices remain stable, increasing demand for overseas goods.

Fall in price level:

• Consumers can afford more as prices decrease.
• Exports become more attractive to foreign buyers.
• Imports become less attractive compared to domestic goods.

Shifts in the AD curve

A shift in the AD curve occurs when factors other than the price level change the total demand for output. These shifts can be to the right (increase in AD) or to the left (decrease in AD).

Rightward shifts in AD

A rightward shift means more output is demanded at any given price level, often leading to higher production and prices for a fixed output.

Factors causing rightward shifts:

• Lower income taxes, which boost disposable income and encourage more spending by households.
• Increased government spending that exceeds tax revenue, injecting extra money into the economy.
• A weaker domestic currency, making exports cheaper and imports more expensive, which improves net exports (exports minus imports).

Leftward shifts in AD

A leftward shift means less output is demanded at any given price level, often resulting in lower production, reduced prices for a fixed output, and falling employment.

Factors causing leftward shifts:

• Higher interest rates, which discourage consumer borrowing and business investment.
• A stronger domestic currency, making exports more expensive and imports cheaper, which worsens net exports.

The multiplier effect

The multiplier effect occurs when an initial injection of spending into the economy leads to a larger overall increase in national income. This happens because the extra money circulates, becoming income for others who then spend a portion of it, creating further demand.

How the multiplier effect works

Money from an injection, such as government investment in infrastructure, generates wages and profits. Recipients spend part of this on goods and services, creating a second round of income for suppliers, and the process continues. Each round is smaller due to leakages like savings, taxes, or imports, until the effect fades.

For example, if the government invests in transport projects, construction workers earn wages and spend on local businesses, boosting those firms' incomes and leading to more hiring and spending in a chain reaction.

The multiplier is also known as the national income multiplier, as it amplifies the impact of the original injection on total economic activity.

Impacts on employment and measurement of the multiplier

Changes in aggregate demand have significant effects on the job market, while measuring the multiplier presents practical challenges.

Effects on employment

Labour demand is derived from the need for output – when AD rises, firms produce more goods and services, increasing their demand for workers. This creates additional jobs and raises employment levels. Conversely, a fall in AD reduces output needs, leading to fewer jobs and higher unemployment.

Challenges in measuring the multiplier

The size of the multiplier depends on the extent of leakages from the economy's circular flow, such as savings or imports, which reduce the amount recirculated. However, it is hard to measure accurately because effects can take years to fully appear due to time lags in spending and production adjustments.