How does a monopoly set price and output, and is monopoly good or bad for welfare?
The monopoly model, barriers to entry, the determination of price and output, the costs and benefits of monopoly, natural monopoly, and sources of monopoly power.
An answer to AQA A-Level Economics 4.1.5, covering the monopoly model, barriers to entry, how price and output are determined, the costs and benefits of monopoly including natural monopoly, and the sources of monopoly power.
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What this dot point is asking
AQA wants you to model a monopoly, explain barriers to entry, show how it sets price and output, weigh the costs and benefits of monopoly (including natural monopoly), and identify the sources of monopoly power. Monopoly is most often examined as a comparison against perfect competition.
The monopoly model
Protected by barriers to entry, the monopolist is a price maker: it faces the downward-sloping market demand curve, so its MR curve lies below AR and falls twice as steeply. To sell an extra unit it must lower the price on all units, which is why MR is below price.
Barriers to entry
Price and output
The monopolist maximises profit where , then charges the price consumers will pay for that output, read up to the AR (demand) curve. Compared with perfect competition (where ), this gives a higher price and lower output. Because barriers to entry block new firms, supernormal profit (AR above ATC) can persist in the long run rather than being competed away.
Costs and benefits
- Costs. Allocative inefficiency (, so consumers value the next unit more than it costs to make), productive inefficiency (output is not at minimum ATC), restricted output and higher prices, possible X-inefficiency (rising costs from a lack of competitive pressure), and a redistribution of welfare from consumers to producers (a deadweight welfare loss).
- Benefits. Economies of scale can lower long-run average cost and even prices below the competitive level; large supernormal profits can fund research and development (dynamic efficiency, as argued by Schumpeter); price discrimination can fund cross-subsidy; and a natural monopoly (one firm supplying the whole market at lowest cost, such as a water network) avoids wasteful duplication of infrastructure.
Sources of monopoly power
Monopoly power comes from a high market share, strong barriers to entry, few close substitutes, and price-inelastic demand that lets the firm raise price with little loss of sales. The greater these are, the more the firm can act as a price maker.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20209 marksUsing a diagram, analyse why a monopoly produces a lower output at a higher price than a perfectly competitive industry with the same costs.Show worked answer →
A 9 mark analysis question rewards a comparative chain plus an accurate diagram.
- Monopoly
- Draw market demand (AR) with MR below it. The monopolist maximises profit at , giving output Qm, then reads price Pm up to AR. Because MR is below AR, occurs at a lower output than .
- Comparison
- A competitive industry produces where price equals MC (supply equals demand), at output Qc above Qm and price Pc below Pm.
- Conclusion
- The monopolist restricts output and raises price to maximise profit, so and . Markers reward locating both equilibria and the explicit MR below AR reasoning.
AQA 20229 marksAssess whether the existence of a natural monopoly justifies it being left in private hands.Show worked answer →
A 9 mark assessment question needs evaluation and a judgement.
- Knowledge
- A natural monopoly exists where economies of scale are so large relative to demand that one firm supplies at lower average cost than several; duplicating networks (water pipes, rail track) would waste resources.
- For private hands
- Profit incentive drives efficiency and investment; cost is lower with a single network.
- Against
- A profit-maximising natural monopoly restricts output and charges above marginal cost, harming consumers, so it usually needs regulation (price caps such as RPI minus X) or public ownership.
- Judgement
- Single ownership is justified to capture economies of scale, but regulation is needed to prevent exploitation. Markers reward a clear, supported stance.
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Sources & how we know this
- AQA A-level Economics (7136) specification — AQA (2015)