AQA A-level Economics: Efficiency, market structure and surplus (7136)

This guide follows the AQA A-level Economics specification (7136), content sections 4.1.5.10 and 4.1.5.11 in the PDF, which the AQA website and our site map number as part of 3.1.5. It covers efficiency, market structure and consumer and producer surplus. Neither section carries an AS-only or A-level-only marker in the specification. Every figure here is made up for practice and is not a real statistic.

Pair it with the revision notes and the practice set. The course hub is AQA A-level Economics, the printable list is the checklist, and you can test yourself with the free diagnostics. Related pages: individuals, firms, markets and market failure and the microeconomics revision notes.

Skills this unit tests

Section	Content	What to practise
4.1.5.10	Static and dynamic efficiency	Define both and apply them to firms
4.1.5.10	Productive efficiency (minimising average total costs) and allocative efficiency (price = marginal cost)	Test whether a firm meets each condition
4.1.5.10	Dynamic efficiency: R&D, investment in human and non-human capital, technological change	Link spending to lower future costs and better products
4.1.5.10	Compare firms in different market structures using conduct and performance indicators	Choose indicators and judge them
4.1.5.11	Consumer and producer surplus, with price discrimination and the deadweight loss of monopoly	Draw, calculate and evaluate

The specification says diagrammatic analysis is expected for surplus. Here the diagrams are described in words and small tables, so redraw each one yourself as you read.

Static and dynamic efficiency

Static efficiency is efficiency at a point in time, with technology and capital fixed. It has two parts: productive and allocative efficiency. Dynamic efficiency is efficiency over time. It asks whether a firm improves products and lowers costs through innovation and investment.

A firm can score well on one and badly on the other. That tension drives most of the evaluation in this unit.

Productive efficiency

Productive efficiency means producing at the output where average total cost (ATC) is at its minimum. No more output can be made from the same resources at a lower cost per unit. Where marginal cost (MC) crosses ATC, ATC is at its lowest point, so MC = ATC at the productively efficient output.

Worked example. A firm in an illustrative market has total cost TC = 450 + 4Q + 0.5Q², so MC = 4 + Q.

Output Q	TC	ATC = TC/Q	MC = 4 + Q
10	540	54.00	14
20	730	36.50	24
30	1,020	34.00	34
40	1,410	35.25	44
50	1,900	38.00	54

ATC falls to 34 at Q = 30, where MC = ATC = 34, then rises. The firm is productively efficient only at Q = 30. At 20 it is not, because ATC is 36.50.

A firm can be productively inefficient by producing too little (spreading fixed costs thinly) or by producing beyond the minimum point. A large firm can also have lower ATC than many small ones. In a natural monopoly, one firm producing 40 units might have ATC of 20, while four firms of 10 units each might have ATC of 35 (illustrative). Do not assume monopoly always means higher costs.

Allocative efficiency

Allocative efficiency means price equals marginal cost (P = MC). Price measures the marginal benefit consumers get from the last unit, and MC measures the marginal cost of the resources used. When P = MC, no reallocation could make someone better off without making someone worse off. If P > MC, society values another unit more than it costs, so output is too low. If P < MC, too many resources are used.

Chain of reasoning. A firm with market power restricts output, so price rises above MC, so units worth more than they cost are not made, so welfare is lost.

Dynamic efficiency

Dynamic efficiency is influenced by, for example:

• Research and development (R&D). New products and cheaper processes.
• Investment in human and non-human capital. Training raises worker productivity (human capital). Machines, software and buildings raise output per worker (non-human capital).
• Technological change. Better methods shift the cost curves downwards over time.

Over time, a dynamically efficient firm sees its ATC curve shift down and its products improve. Finance matters. R&D is costly and uncertain, so supernormal profit can pay for it. But a firm facing little rivalry may feel no pressure to innovate, whereas a firm under threat from rivals may have strong incentives to do so.

Comparing market structures: conduct and performance

The specification asks you to understand how conduct and performance indicators compare structures. Conduct is how firms behave. Performance is the results.

Indicator type	Examples	What it can show
Conduct	Pricing policy, output decisions, advertising, R&D and investment spending, collusion or rivalry, entry barriers	Whether the firm competes or uses market power
Performance (static)	Price, profit margin, unit costs, output, quality and variety, consumer surplus	Closeness to P = MC and minimum ATC
Performance (dynamic)	New products introduced, falling costs over time, productivity growth	Whether innovation is happening

Typical pattern, with exceptions. In long-run perfect competition, firms produce where P = MC at minimum ATC, so both static conditions hold, though there may be little supernormal profit to fund R&D. A monopoly usually charges P above MC and may produce below the minimum-ATC output, but may innovate if barriers protect its profit. Monopolistic competition and oligopoly sit between these.

Evaluating an indicator. A high profit margin may come from market power or from low costs. Falling prices may come from rivalry or from technology. Always ask what else could explain the number, and whether you are comparing like with like.

Consumer and producer surplus

Consumer surplus (CS) is what buyers gain by paying less than the most they would have offered. On a diagram it is the triangle between the demand curve and the price line, up to the quantity traded. Producer surplus (PS) is the gap between the price received and the minimum price producers would accept (the supply or MC curve). It is the area between the price line and the supply curve.

Worked example (illustrative market). Demand is P = 64 − Q and market supply, which is the sum of the firms’ MC curves, is P = 4 + Q.

Step	Working	Result
Equilibrium	64 − Q = 4 + Q, so Q = 30	P = 34
Consumer surplus	0.5 × 30 × (64 − 34)	450
Producer surplus	0.5 × 30 × (34 − 4)	450
Total surplus	450 + 450	900

At the equilibrium, P = MC, so the market is allocatively efficient and total surplus is at its maximum.

Deadweight loss of monopoly

Suppose one firm now supplies this market with the same marginal cost curve, MC = 4 + Q. It sets MR = MC. Demand P = 64 − Q gives MR = 64 − 2Q.

Step	Working	Result
Profit-maximising output	64 − 2Q = 4 + Q, so Q = 20	Q = 20
Price	64 − 20	P = 44
MC at Q = 20	4 + 20	24
Consumer surplus	0.5 × 20 × (64 − 44)	200
Producer surplus	20 × (44 − 24) + 0.5 × 20 × (24 − 4) = 400 + 200	600
Deadweight loss	0.5 × (30 − 20) × (44 − 24)	100

Check: 200 + 600 + 100 = 900, the competitive total. Compared with competition, CS falls by 250, PS rises by 150, and the other 100 is lost to everyone. That 100 is the deadweight loss: the triangle between the demand curve and the MC curve over the units not produced, from Q = 20 to Q = 30. Sketch:

Price
 64 |\ D
 44 |-\-----.  monopoly price
 34 |  \     \. competitive price
 24 |   ....X  MC at monopoly output
  4 |  ____/   MC (supply)
    +------------ Quantity
        20  30

The shaded deadweight loss triangle has corners at the monopoly point (20, 44), the point on MC at Q = 20 (24) and the competitive point (30, 34).

Price discrimination and surplus

Price discrimination is selling the same good at different prices where differences in cost do not explain the gap. Its effect on surplus depends on the type. (How and when it is possible belongs to the unit on monopoly power.)

Perfect price discrimination. Each consumer pays their maximum willingness to pay. In the market above, output is 30 where the last buyer pays 34 = MC. CS falls to 0, PS rises to 900 and deadweight loss is 0. It is allocatively efficient but all the gain goes to the firm, which raises concerns about fairness.

Third-degree price discrimination, worked. A seller has constant MC = 12 and two groups. Group A: P = 56 − Q. Group B: P = 36 − Q (illustrative). For each group, MR = MC.

	Group A	Group B	Total
MR = MC	56 − 2Q = 12, Q = 22	36 − 2Q = 12, Q = 12	34
Price	34	24
Profit	22 × 22 = 484	12 × 12 = 144	628
CS	0.5 × 22 × 22 = 242	0.5 × 12 × 12 = 72	314

With one price for everyone, the combined demand (for prices up to 36) is Q = 92 − 2P, so P = 46 − 0.5Q and MR = 46 − Q. Setting MR = 12 gives Q = 34 and P = 29. Group A buys 27 and group B buys 7. Profit = 34 × 17 = 578. CS = 0.5 × 27 × 27 + 0.5 × 7 × 7 = 389.

	Single price	Discrimination
Output	34	34
Profit	578	628
Consumer surplus	389	314
Profit + CS	967	942

Competitive total surplus here is 1,256 (968 from A plus 288 from B), so the deadweight loss is 289 under a single price and 314 under discrimination. Total output is unchanged, but sales are shifted between the groups, so it is slightly worse. Profit rises by 50, CS falls by 75.

Discrimination can raise welfare when it increases output, for example by making it worthwhile to serve a low-income group at all, or when extra profit funds investment. It can lower welfare when output stays the same or falls. The answer depends on the numbers, so say so.

Evaluating static against dynamic efficiency

Take the monopoly above and suppose its profit funds R&D which changes MC to 4 + 0.5Q. At MR = MC: 64 − 2Q = 4 + 0.5Q gives Q = 24, P = 40. CS = 0.5 × 24 × 24 = 288. PS = 40 × 24 − (4 × 24 + 0.25 × 24²) = 960 − 240 = 720. Total surplus is 1,008, above the 900 of the competitive market without innovation. So a static loss can be outweighed by dynamic gains.

But consumers still get less (288) than the original 450. A competitive market with that same improved technology would reach Q = 40, P = 24, with CS 800 and PS 400. Judgements depend on whether:

• the monopoly really invests, or keeps profit
• competitive firms could innovate anyway, perhaps under rivalry
• the time period is long enough for gains to appear
• you look at consumers, producers or society

Common errors

• Saying productive efficiency means producing the most output, rather than at minimum ATC.
• Writing P = MR for allocative efficiency instead of P = MC.
• Shading the whole CS triangle as deadweight loss. Only the lost trade is deadweight loss.
• Forgetting that monopoly profit is a transfer and not a loss to society.
• Claiming monopoly is always dynamically efficient or always inefficient. Argue from the evidence.

Official syllabus

Source: the AQA specification for AS and A-level Economics (versions 7135 and 7136), for first teaching from September 2015, version 1.3, covering content sections 4.1.5.10 and 4.1.5.11 (website numbering 3.1.5).