The characteristics of AD — Edexcel A-Level Economics A
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The characteristics of AD explained
Aggregate demand (AD) is the total planned spending on an economy's goods and services at each price level, comprising consumption, investment, government spending and net exports.
Read the full explanation
The AD curve plots this relationship between the general price level and real output. A movement along the AD curve occurs only when the price level itself changes, causing a change in the quantity of real output demanded; this is shown as a slide from one point to another on the same curve. A shift of the AD curve occurs when a non-price determinant changes, such as disposable income, business confidence, government policy or the exchange rate, altering the quantity demanded at every price level. For example, a rise in the price level moves the economy up along the AD curve, reducing real output demanded, whereas a fall in consumer confidence shifts the whole AD curve to the left.
Your focus
- Distinguish between a movement along the AD curve and a shift of the AD curve.
- Identify the cause of each: price level changes for movements, non-price determinants for shifts.
- Illustrate both a movement and a shift correctly on an AD diagram.
The characteristics of AD exam tips
Marking Points
- Define AD as total planned spending on domestic output at each price level, made up of C + I + G + (X − M).
- State that a movement along the AD curve is caused solely by a change in the general price level, shown as a change in the quantity of real output demanded on the same curve.
- State that a shift of the AD curve is caused by a change in a non-price determinant of AD, such as disposable income, confidence, interest rates, government spending or exchange rates.
- Explain that a shift changes the quantity of AD at every price level, moving the whole curve left or right, whereas a movement does not change the position of the curve.
- Apply the distinction to a diagram: label axes as price level and real output, and show either a slide along one AD curve or a new AD curve drawn to the left or right.
Examiner Tips
- 💡In multiple-choice questions, check whether the change described is in the price level or in a non-price determinant; price level means movement, non-price means shift.
- 💡Practise drawing both a movement and a shift on the same axes so you can quickly identify the correct diagram in an option.
- 💡Read each option carefully: distractors often mix a price-level change with a shift, or a determinant change with a movement.
Common Mistakes
- Confusing a change in the price level with a change in a determinant of AD: a price-level change causes a movement along the curve, not a shift; correct this by linking shifts only to non-price factors.
- Thinking that a rise in government spending shifts the AD curve along its length: it shifts the whole curve to the right because spending changes at every price level; correct by drawing a new curve.
- Labelling a movement along the AD curve as a shift: a movement stays on the same curve and changes the quantity demanded; correct by keeping the original curve and marking two points on it.
- Assuming any change in spending automatically shifts AD: only changes in the components of AD at a given price level shift the curve; a price-level change alone moves along it.