COMM1100 Chap.8 Economic Surplus and the Case for Markets
Economic Surplus and the Case for Markets
How should we judge whether a market does a good job? The Week 3 lecture proposes economic surplus: the gap between what buyers are willing to pay and what they pay, plus the gap between what sellers receive and their costs.
Under perfect competition the market maximises that total, because the cheapest producers sell, the buyers who value the good most buy, and every trade worth making happens.
This chapter computes consumer and producer surplus as triangles, shows how a minimum price shrinks the market and destroys surplus, and sets out the caveats the lecture insists on: efficiency is not equity, willingness to pay reflects ability to pay, and surplus judges outcomes, not how they are reached.
Surplus gives the course a common yardstick for comparing very different decisions, from a price cap to a tax to a firm’s pricing strategy.
In the case study it lets you say not only who wins and who loses from a decision, but whether the total value created rises or falls, which is a stronger argument than listing winners and losers.
What this chapter covers
- 01
What markets decide: who makes, who gets, how much
- 02
Alternatives to markets: planners, queues and personal ties
- 03
Consumer, producer and total surplus
- 04
Why competitive equilibrium maximises total surplus
- 05
Price floors and lost surplus
- 06
The invisible hand and resource allocation across markets
- 07
Equity, ability to pay and other caveats
Worked example · free
Surplus in a weekend farmers' market for honey
- +1Set 60 − 2P = 4P − 12, so 6P = 72, P = $12 and Q = 36 jars.
- +1Demand meets the price axis at $30 and supply at $3.
- +1Consumer surplus is ½ × 36 × (30 − 12) = $324; producer surplus is ½ × 36 × (12 − 3) = $162.
- +1Total surplus is $486, the largest total any quantity of honey can generate in this market.
Key terms
- Consumer surplus
- Buyers' willingness to pay minus the price paid, summed over units: the area below demand and above price.
- Producer surplus
- The price received minus marginal cost, summed over units: the area above supply and below price.
- Total surplus
- The sum of consumer and producer surplus; the course's measure of how much value a market creates.
- Price floor
- A legal minimum price; set above equilibrium, it reduces the quantity traded and lowers total surplus.
- Invisible hand
- The idea that self-interested buyers and sellers, guided by prices, collectively maximise total surplus.
- Efficiency
- An allocation that maximises total economic surplus; it need not be equitable.
Economic Surplus and the Case for Markets FAQ
Why does a competitive market maximise total surplus?
Sellers with the lowest marginal cost do the selling, buyers with the highest marginal benefit do the buying, and trade continues until the last unit’s marginal benefit equals its marginal cost, so no further trade could add surplus.
What is wrong with selling more than the equilibrium quantity?
Beyond equilibrium, the extra units cost sellers more to make than they are worth to buyers. Each such trade has negative surplus, so forcing it reduces the total.
Does an efficient market mean a fair outcome?
Not necessarily. The lecture warns that an efficient result can still be unfair, that what people will pay depends on what they can afford, and that surplus judges results rather than the process that produced them.
How do I calculate lost surplus from a price floor?
Find the quantity buyers take at the floor, then the triangle between that quantity and the equilibrium quantity, bounded by demand above and supply below. Its area, half of base times height, is the surplus lost.
What alternatives to markets does the lecture consider?
It asks you to compare markets with a central planner deciding everything, first come first served queuing, and giving goods to friends and family. Judged by total surplus, none of these does systematically better than a perfectly competitive market, although each may score differently on fairness.
Assessment move
Draw every surplus question before calculating it: shade the consumer triangle above the price and the producer triangle below, mark the intercepts, then compute. Practise one equilibrium question and one price-floor question each session. For written answers, keep the two kinds of claim separate: whether the total is as large as possible, and whether its distribution is acceptable.
The second needs the normative lens from the first week.
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