OxfordAQA International AS and A-level Economics: Dynamics, efficiency, surplus (9640) – Revision Notes

These notes condense sections 3.3.3.8 to 3.3.3.10 of the OxfordAQA International AS and A-level Economics (9640) specification, version 1.2: competitive dynamics, static and dynamic efficiency, and consumer and producer surplus. The specification places section 3.3 in the extra International A2 content. All figures are invented and illustrative. For fuller explanations and longer examples, use the study guide, then try the practice questions.

Course pages: the OxfordAQA A-level Economics hub, the printable checklist and the free diagnostics. Related AS-level notes: markets and monopoly power.

3.3.3.8 Dynamics of competition

• Firms compete on price, product quality, cost reduction and service, not on price alone.
• Short-run benefits: lower prices, choice and better service.
• Long-run benefits: lower unit costs and new products as firms invest and new firms enter.
• Creative destruction: large profit from monopoly power attracts entrants who innovate past barriers to entry. The new product or process destroys the old firm’s position. The specification calls it a fundamental feature of competition in a market economy.

Reasoning chain

1. A firm has monopoly power and earns large profit.
2. Profit signals a reward for entering and innovating.
3. A new firm finds a cheaper process or a better product.
4. Price falls or quality rises, so consumers gain.
5. The incumbent’s profit falls, so it must innovate or lose out.

Evaluation: high barriers slow the process; duplicated research is wasteful; takeovers can remove the challenger; the destruction costs jobs and sunk capital.

Worked reminder (invented). An incumbent sells 20,000 units at 25 with unit cost 15. A new entrant with unit cost 12 enters. The price falls to 20, the incumbent sells 12,000 and the entrant 14,000. Incumbent profit falls from 10 x 20,000 = 200,000 to 5 x 12,000 = 60,000, a fall of 70%. The entrant makes 8 x 14,000 = 112,000. Price falls 20% and market output rises 30%.

3.3.3.9 Efficiency

Concept	Definition	Test
Static efficiency	Efficiency at a point in time	Productive and allocative
Productive efficiency	Lowest cost per unit	Output at minimum ATC, where MC = ATC
Allocative efficiency	Output matches what consumers value	P = MC
X-inefficiency	Actual cost above the lowest possible cost	Actual ATC greater than minimum ATC
Dynamic efficiency	Efficiency over time	R&D, skills and capital spending, technological change

Method: find productive efficiency

1. Write ATC = TC/Q (or use a table).
2. Find the output with the lowest ATC.
3. Check that MC equals ATC there.

Example: TC = 200 + 4Q + 0.02Q². ATC = 200/Q + 4 + 0.02Q, MC = 4 + 0.04Q. Setting MC = ATC: 200/Q = 0.02Q, so Q² = 10,000 and Q = 100. ATC = 2 + 4 + 2 = 8 and MC = 8.

X-inefficiency reminder

If actual ATC is 10 against a minimum of 8, the excess is 2, which is 25% above the minimum. At 100 units the waste is 200.

Dynamic efficiency reminder

A firm spends 90,000 on R&D that cuts unit cost by 1.50 on 40,000 units a year. Annual saving = 60,000. Payback = 90,000/60,000 = 1.5 years.

Conduct and performance indicators

Conduct	Performance
Pricing behaviour, advertising, R&D spending, entry strategies	Profit, price, unit cost, productivity, quality, innovation

Use them to compare market structures. High concentration alongside a wide price-cost gap and low R&D suggests weaker static and dynamic performance, but one indicator can mislead (economies of scale can justify a large firm).

Key distinctions

• Productive efficiency is about cost (minimum ATC). Allocative efficiency is about price against marginal cost.
• Static efficiency can conflict with dynamic efficiency: a monopoly may have a deadweight loss now but fund innovation that lowers costs later.
• X-inefficiency is a cost curve that sits too high. Productive inefficiency is being at the wrong point on the curve.

3.3.3.10 Consumer and producer surplus

Term	Meaning	Area
Consumer surplus (CS)	Willingness to pay minus price paid	Between demand and the price line
Producer surplus (PS)	Price received minus minimum supply price	Between the price line and supply (MC)
Deadweight loss (DWL)	Surplus lost to everyone	Triangle between demand and MC over the output not produced

Diagrammatic analysis is expected, so practise drawing the diagrams.

Method: surplus from linear curves

1. Find equilibrium by setting demand price equal to supply price.
2. CS = half x Q x (demand intercept - P).
3. PS = half x Q x (P - supply intercept).
4. For monopoly, set MR = MC (MR has the same intercept as demand and twice the slope), then read price from demand.

Monopoly check (invented). Demand P = 40 - Q, constant MC = 10. Competition: Q = 30, P = 10, CS = 450. Monopoly: MR = 40 - 2Q = 10 gives Q = 15 and P = 25. CS = half x 15 x 15 = 112.5, PS = 15 x 15 = 225 and DWL = half x 15 x 15 = 112.5. Check: 112.5 + 225 + 112.5 = 450.

Applications

• Monopoly: CS falls, PS rises, DWL appears.
• Perfect price discrimination: output rises to the competitive level, CS is zero, PS takes everything, DWL is zero.
• Third-degree discrimination: profit rises, CS usually falls and total welfare can rise or fall. It depends on whether output rises and on how it is shared between groups.
• Tariff: CS falls, domestic PS rises, government revenue appears and DWL arises on both the extra home output and the lost consumption.

Tariff identity: loss of CS = gain in PS + tariff revenue + DWL.

Tariff reminder (invented). A small importer has domestic demand P = 80 - 4Q and domestic supply P = 8 + 4Q. The world price is 24 and a tariff of 8 lifts the domestic price to 32.

	P = 24	P = 32
Demand	14	12
Supply	4	6
Imports	10	6

• Loss of CS = half x (14 + 12) x 8 = 104.
• Gain in PS = half x (4 + 6) x 8 = 40.
• Tariff revenue = 8 x 6 = 48.
• DWL = half x 2 x 8 + half x 2 x 8 = 16.
• Check: 40 + 48 + 16 = 104.

Third-degree reminder. With constant MC = 10 and demands P = 50 - 2Q and P = 30 - 2Q, charging each group its own price gives profit 250, against 225 for a single price. CS falls from 162.5 to 125 and total surplus falls from 387.5 to 375. Output is 15 in both cases, so the loss comes from an unequal split of the output between groups.

Evaluation prompts

• Who gains and who loses? Name consumers, producers and the government.
• Is the loss static only, or does innovation offset it over time?
• Does the threat of entry (contestability) discipline the firm even without actual rivals?
• Does MC include external costs? If not, surplus overstates welfare.
• Is the surplus measurable? Willingness to pay depends on income.

Quick self-test

1. What must be true of output for a firm to be productively efficient?
2. A firm has TC = 200 + 4Q + 0.02Q². At what output is ATC at its minimum, and what is ATC there?
3. The firm in question 2 has an actual ATC of 10 at 100 units. How much extra cost is there in total, and what percentage above the minimum is it?
4. Demand is P = 50 - Q and supply is P = 8 + 2Q. Find equilibrium and total surplus.
5. Demand is P = 40 - Q and constant MC = 10. Find the monopoly output and price, and the deadweight loss.
6. Using question 5, what happens to CS, PS and DWL under perfect price discrimination?
7. A firm spends 90,000 on R&D that cuts unit cost by 1.50 on 40,000 units a year. Find the payback period.
8. A firm sells at 25 where MC = 10. Is it allocatively efficient? Explain.
9. Name two parts of the tariff diagram that are transfers rather than losses.
10. Suggest one barrier that could slow creative destruction.

Answers

1. Output at the minimum of average total cost, where MC = ATC.
2. Q = 100, ATC = 8 (MC is also 8).
3. Excess per unit = 2, so 200 in total; 2/8 = 25% above the minimum.
4. 50 - Q = 8 + 2Q gives Q = 14 and P = 36. CS = half x 14 x 14 = 98, PS = half x 14 x 28 = 196, total 294.
5. Q = 15, P = 25. DWL = half x 15 x 15 = 112.5.
6. Output is 30, CS = 0, PS = half x 30 x 30 = 450 and DWL = 0.
7. 1.5 years (90,000/60,000).
8. No. P exceeds MC by 15, so consumers value extra units above their cost and too little is produced.
9. The consumer surplus transferred to producers and the tariff revenue transferred to the government.
10. Patents, large sunk costs or control of supply raise barriers to entry.

Where marks are usually lost

• Using MR = price for allocative efficiency.
• Locating productive efficiency at the lowest MC instead of the lowest ATC.
• Drawing the DWL triangle without a corner at the monopoly point.
• Forgetting the half in surplus triangles, or using the wrong intercept.
• Calling surplus transferred to producers a loss to society.
• Judging monopoly on static efficiency only, with no mention of dynamic efficiency or contestability.
• Naming creative destruction without a chain showing profit, entry and innovation.
• Stating a conclusion about welfare without saying who gains, who loses and what it depends on.

Official syllabus

OxfordAQA International AS and A-level Economics (9640), specification version 1.2, sections 3.3.3.8 to 3.3.3.10. First teaching September 2020, first AS exams May/June 2021, first A-level exams May/June 2022. Published by OxfordAQA.