What happens when a government sets a price above or below the market level?
Explain maximum and minimum price controls and the shortages or surpluses they create
A clear O-Level answer on price controls. How a maximum price (ceiling) below equilibrium causes a shortage, how a minimum price (floor) above equilibrium causes a surplus, why governments use them, and their side effects.
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What this dot point is asking
The syllabus wants you to explain maximum and minimum price controls, and the shortages or surpluses they create. The big idea is that when a government sets a price away from the market equilibrium, the quantity demanded and quantity supplied no longer match, so the control has predictable side effects that an exam answer must trace through.
The answer
What price controls are
A price control is a price set by the government, by law, that the market is not allowed to cross. There are two kinds: a maximum price (a ceiling) and a minimum price (a floor). To have any effect, each must be set on the binding side of the equilibrium.
Maximum price (price ceiling)
A maximum price is used to keep a good affordable, for example rent or basic foods. But at the lower controlled price:
- Quantity demanded rises (the good is cheaper, so more people want it).
- Quantity supplied falls (producers offer less at the lower price).
Quantity demanded now exceeds quantity supplied, so there is a shortage. Because not everyone can get the good, it must be rationed another way, such as long queues, waiting lists, or an illegal black market where the good is sold above the legal price.
Minimum price (price floor)
A minimum price is used to protect producers (such as guaranteeing farmers an income) or to discourage consumption (such as a high minimum price for alcohol). But at the higher controlled price:
- Quantity supplied rises (producers want to sell more at the higher price).
- Quantity demanded falls (fewer people buy at the higher price).
Quantity supplied now exceeds quantity demanded, so there is a surplus of unsold goods. The government may have to buy up or store the surplus, which is costly.
The minimum wage as a price floor
A minimum wage is a price floor in the labour market. If it is set above the equilibrium wage, the quantity of labour supplied (people wanting jobs) rises while the quantity demanded (jobs offered by firms) falls. The surplus of labour is unemployment. This is why the level of a minimum wage matters so much.
Examples in context
Example 1. Rent controls and housing shortages. Cities that have capped rents below the market level have often ended up with shortages of rental housing, long waiting lists and poorly maintained flats, because landlords reduce supply at the controlled rent. This illustrates the shortage that a price ceiling predictably creates.
Example 2. A minimum price for alcohol. Some governments set a minimum price per unit of alcohol, above the market price, to discourage heavy drinking, a demerit good. The higher floor reduces the quantity demanded, supporting the health aim, but can create a surplus and may push some buyers toward cheaper, illegal sources.
Try this
Cue. Define a maximum price and state where it must be set to have an effect. A legal limit above which the price may not rise; to have an effect it must be set below the equilibrium price.
Cue. Explain why a maximum price below equilibrium causes a shortage. At the lower price, quantity demanded rises and quantity supplied falls, so quantity demanded exceeds quantity supplied, leaving a shortage.
Cue. Explain how a minimum wage set above the equilibrium wage can cause unemployment. At the higher wage, more workers want jobs (quantity of labour supplied rises) but firms offer fewer jobs (quantity demanded falls), so the surplus of labour is unemployment.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original6 marksExplain why a maximum price set below the equilibrium price leads to a shortage, and state one side effect of such a policy.Show worked answer →
A 6 mark question rewards the demand-and-supply reasoning and a valid side effect.
Why a shortage results. A maximum price below equilibrium makes the good cheaper. At this lower price, quantity demanded rises (more people want it) while quantity supplied falls (producers offer less). Quantity demanded now exceeds quantity supplied, so there is a shortage.
Side effect. Because not everyone who wants the good can get it, the good must be rationed in some other way, such as long queues, waiting lists, or a black market where the good is sold illegally above the maximum price.
Markers reward the point that the lower price raises quantity demanded and lowers quantity supplied, the resulting shortage, and one valid side effect such as queues or a black market.
Original6 marksExplain why a government might set a minimum price above the equilibrium, and explain the surplus this creates.Show worked answer →
A 6 mark question rewards a reason for the minimum price and the surplus reasoning.
- Reason for a minimum price
- A government may set a minimum price (floor) above equilibrium to protect producers, such as guaranteeing farmers a fair income, or to discourage consumption of a good such as alcohol by keeping its price high.
- Why a surplus results
- At the higher minimum price, quantity supplied rises (producers want to sell more) while quantity demanded falls (fewer people buy at the higher price). Quantity supplied now exceeds quantity demanded, so there is a surplus of unsold goods.
- Consequence
- The government may have to buy up the surplus or store it, which is costly. For a good such as labour, a minimum wage above equilibrium can create a surplus of labour, that is, unemployment.
Markers reward a valid reason for the floor, the point that the higher price raises quantity supplied and lowers quantity demanded, and the resulting surplus, ideally with a real consequence.
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