Edexcel A Level Economics A:复习笔记2.2.1 The Characteristics of AD

The Components of AD

  • Aggregate demand (AD) is the total demand for all goods/services in an economy at any given average price level
  • Its value is often calculated using the expenditure approach
    • AD = Consumption (C) + Investment (I) + Government spending (G) + (Exports-Imports) (X-M)
    • AD = C + I + G + (X-M)
  • If AD increases then economic growth has occurred and vice versa
  • Consumption is the total spending on goods/services by consumers (households) in an economy
  • Investment is the total spending on capital goods by firms
  • Government spending is the total spending by the government in the economy:
    • Includes public sector salaries, payments for provision of merit and public goods etc.
    • It does not include transfer payments
  • Net exports are the difference between the revenue gained from selling goods/services abroad and the expenditure on goods/services from abroad
    • Individuals, firms and governments export/import

The relative importance of the components of AD

  • Depending on the country, the value of each component and its contribution to AD can vary significantly:
    • Government spending in Sweden is 53% of AD and in the UK, it is 25% of AD
  • The % that each component contributes to AD in the UK is approximately
    • Consumption: 60%
    • Investment: 14%
    • Government spending: 25%
    • Net Exports: 1%
  • A 1 % increase in consumption or government spending will have a much larger impact on economic growth than a 1% increase on net exports

The AD Curve

  • The relationship between the average price level and the total output in an economy is shown with an aggregate demand (AD) curve


A diagram showing the aggregate demand (AD) curve for an economy with Average Price Level on the Y axis and Real GDP on the X axis


  • The AD curve is downward sloping due to three reasons:
  1. The interest rate effect: At higher average price (AP) levels, there are likely to be higher interest rates. Higher interest rates reduce investment and are an incentive for households to save - and vice versa
  2. The wealth effect: As AP increases, the purchasing power of households decreases and the AD falls - and vice versa
  3. The exchange rate effect: As AP falls, interest rates are likely to fall too. Lower interest rates lower the exchange rate. With a lower exchange rate, the economy's goods/services are more attractive abroad and exports increase, thereby increasing real GDP

A Movement Along The AD Curve

  • Whenever there is a change in the average price level (AP)  in an economy, there is a movement along the aggregate demand (AD) curve


A diagram showing an increase and decrease in the average price level (AP) which causes a movement along the aggregate demand (AD) curve leading to a contraction/expansion of AD


Diagram Analysis

  • An increase in the AP (ceteris paribus) from AP1 → AP2 leads to a movement along the AD curve from A → B
    • There is a contraction of real GDP from Y1 → Y2
  • A decrease in the AP (ceteris paribus) from AP1 → AP3 leads to a movement along the AD curve from A → C
    • There is an expansion of real GDP (output) from Y1 → Y3

A Shift of the Entire AD Curve

  • Whenever there is a change in any of the determinants ofaggregate demand (AD) in an economy, there is a shift of the entire AD curve


A diagram showing a shift in the entire aggregate demand (AD) curve due to a change in one of the determinants of AD


Diagram Analysis

  • An increase in any one of the determinants ofaggregate demand (AD) results in a shift right of the entire curve from AD1 → AD2
    • At every price level, real GDP has increased from Y1 → Y2
  • A decrease in any one of the determinants of AD results in a shift left of the entire curve from AD1 → AD3
    • At every price level, real GDP has decreased from Y1 → Y3