Shift in Demand and Movement along Demand Curve

A shift in demand means at the same price, consumers wish to buy more. A movement along the demand curve occurs following a change in price.

Movement along the demand curve

A change in price causes a movement along the demand curve.

movement-along-demand-curve

An increase in price from $12 to $16 causes a movement along the demand curve, and quantity demand falls from 80 to 60.

A change in price doesn’t shift the demand curve – we merely move from one point of the demand curve to another.

Shift in the Demand Curve

shift-in-demand

A shift in the demand curve occurs when the whole demand curve moves to the right or left. For example, an increase in income would mean people can afford to buy more widgets even at the same price.

The demand curve could shift to the right for the following reasons:

  • The good became more popular (e.g. fashion changes or successful advertising campaign)
  • The price of a substitute good increased.
  • The price of a complement good decreased.
  • A rise in incomes (assuming the good is a normal good, with positive YED)
  • Seasonal factors.

Evaluation – Time period

In the real world, a higher price could cause a movement along the demand curve, but in the long-term, it could cause a shift as consumers respond to the persistently higher prices.

For example, if there is an increase in the price of petrol, there would be a movement along the demand curve, and a smaller quantity would be bought. However, there is likely to be only a small fall in demand because the demand for petrol tends to be quite price inelastic.
higher-price-oil-elasticity-time-lag
However, in the long term, the demand curve may shift to left as well because people respond to the higher price by looking for alternatives, for example, they buy an electric car and so no longer need petrol.
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