📚 The Theory of Contestable Markets | 可竞争市场理论
In traditional microeconomics, the degree of competition in a market is usually judged by the number of firms and the concentration ratio. The theory of contestable markets, developed by William Baumol, John Panzar and Robert Willig in 1982, challenges this view. It argues that what matters for competitive outcomes is not the number of firms currently in the market, but the ease with which new firms can enter and leave the market. A market can behave competitively even with only one dominant firm, provided that the threat of entry is strong.
在传统微观经济学中，市场竞争程度通常以企业数量和集中度来衡量。由鲍莫尔、潘泽和威利格于1982年提出的可竞争市场理论挑战了这一观点。该理论认为，决定竞争性结果的关键不在于现有企业的数量，而在于新企业进入和退出市场的难易程度。只要进入威胁足够强烈，即使市场上只有一家主导企业，其行为结果也可能与竞争性市场无异。
1. Definition of a Contestable Market | 可竞争市场的定义
A contestable market is one in which there are no significant barriers to entry or exit, so that potential competitors can enter the market at virtually zero cost and leave without losing invested capital. The key feature is not the number of existing firms, but the vulnerability of incumbents to hit-and-run entry. If a market is perfectly contestable, even a monopoly must price in a way that prevents profitable entry from occurring.
可竞争市场是指进入或退出市场均不存在显著壁垒的市场，潜在竞争者可以在几乎零成本的情况下进入市场，并在不损失已投入资本的前提下退出。其关键特征不在于现有企业的数量，而在于在位者面对”打了就跑”式进入时的脆弱性。如果市场完全可竞争，即使是垄断企业也必须将价格定在足以阻止有利可图的进入发生的水平上。
2. Key Conditions for Contestability | 可竞争市场的关键条件
Three conditions are generally required for a market to be contestable. First, there are no sunk costs: any capital spent on entry can be fully recovered if the firm decides to exit. Second, there is free entry and exit: potential entrants have the same technology, information and cost functions as incumbents, and there are no legal or regulatory obstacles to entry. Third, consumers respond quickly to price differences, meaning that an entrant can attract customers away from an incumbent almost immediately.
市场若要具备可竞争性，通常需要满足三个条件。第一，不存在沉没成本：企业进入时所投入的资本如果决定退出，可以完全收回。第二，进入和退出自由：潜在进入者与在位者拥有相同的技术、信息和成本函数，并且不存在法律或制度上的进入障碍。第三，消费者能对价格差异迅速作出反应，这意味着进入者几乎能立即从在位者手中吸引走客户。
3. The Central Role of Sunk Costs | 沉没成本的核心地位
Sunk costs are costs that cannot be recovered once they have been incurred, such as advertising expenditure, market research fees, or installation of machinery that has no resale value. In contestable market theory, sunk costs are far more important than fixed costs. Even if a market requires a high level of fixed investment, it can still be contestable as long as that investment is recoverable. The presence of sunk costs creates a risk for potential entrants: if entry fails, part of the capital is permanently lost, which discourages entry and weakens market discipline.
沉没成本是指一旦发生便无法收回的成本，例如广告支出、市场调研费用或没有转售价值的专用设备安装成本。在可竞争市场理论中，沉没成本远比固定成本更为重要。即使一个市场需要高额固定投资，只要这些投资能够收回，该市场仍然是可竞争的。沉没成本的存在给潜在进入者带来了风险：如果进入失败，部分资本将永久损失，这会使进入意愿下降，从而削弱市场竞争纪律的约束力。
4. The Logic of Hit-and-Run Entry | “打了就跑”式进入的逻辑
If entry and exit are free and no sunk costs exist, a potential entrant can adopt a hit-and-run strategy. This means that the entrant can quickly move into the market when it sees the incumbent earning supernormal profit, undercut the incumbent’s price, capture market share and earn profit for a short period, and then leave without cost if the incumbent retaliates. The mere existence of this possibility disciplines incumbents: they know that any supernormal profit will be quickly eliminated by entry, so they behave as if they were in a highly competitive market.
如果进入和退出自由且不存在沉没成本，潜在进入者就可以采取”打了就跑”的策略。也就是说，当进入者发现在位者正在赚取超额利润时，它可以迅速进入市场，以更低的价格抢占市场份额，在短期内赚取利润，如果遭遇在位者报复，则可以无成本退出。这种可能性的存在本身就对在位者形成了约束：在位者知道任何超额利润都会因进入而迅速消失，因此它们的行为表现得仿佛处于高度竞争的市场之中。
5. Pricing Behaviour in a Contestable Market | 可竞争市场中的定价行为
In a perfectly contestable market, the incumbent cannot earn supernormal profit in the long run. If it tries to raise price above average cost, the resulting profit attracts hit-and-run entrants. The price is therefore pushed down towards average cost, and output is expanded towards the socially efficient level. However, unlike perfect competition, price may not exactly equal marginal cost: if economies of scale exist, a natural monopoly can survive in a contestable market by practicing average cost pricing, which is the maximum price sustainable against entry.
在完全可竞争市场中，在位者长期内无法赚取超额利润。如果在位者试图将价格提高到平均成本以上，由此产生的利润就会吸引”打了就跑”的进入者。因此价格会被压低至平均成本水平，产量也会扩大到接近社会有效率的水平。然而，与完全竞争不同的是，价格未必恰好等于边际成本：如果存在规模经济，自然垄断企业可以通过平均成本定价在可竞争市场中继续存活，这是面对进入压力时所能维持的最高价格。
6. Contestable Markets versus Perfect Competition | 可竞争市场与完全竞争的对比
Perfect competition requires many small firms, a homogeneous product, perfect information and no barriers to entry. A contestable market requires only freedom of entry and exit and zero sunk costs. The outcome in terms of profit and efficiency can be similar, but the structural assumptions are very different. In perfect competition, the large number of firms drives price down; in a contestable market, the threat of entry drives price down. A market with only two or three firms, or even one firm, can therefore produce competitive outcomes if it is contestable.
完全竞争要求市场上有大量小型企业、同质产品、完全信息和不存在进入壁垒。而可竞争市场只要求进入和退出自由以及零沉没成本。二者的利润水平和效率结果可能相似，但结构性假设差异显著。在完全竞争中，大量企业的存在压低了价格；在可竞争市场中，进入的威胁压低了价格。因此，只要市场可竞争，只有两三家甚至一家企业的市场也能产生竞争性的结果。
7. Contestable Markets versus Monopoly | 可竞争市场与垄断的对比
A pure monopoly is often assumed to produce less output and charge a higher price than a competitive market, generating a welfare loss. But in a contestable market, a monopolist is constrained by potential competition. If the monopolist charges a price above average cost, it invites entry; if the monopolist knows this, it will adopt a limit pricing strategy that just allows normal profit. The result is that the monopolist produces much closer to the efficient output level than the traditional textbook monopoly model would predict. Market power is therefore determined by barriers to entry, not by market share alone.
人们通常认为纯粹垄断者比竞争市场生产的产量更少、价格更高，并造成福利损失。但在可竞争市场中，垄断者受到潜在竞争的约束。如果垄断者定价高于平均成本，就会招致进入；如果垄断者意识到这一点，它就会采取限制性定价策略，将利润维持在正常利润水平。结果是垄断企业的产量比传统教科书垄断模型所预测的要更接近有效产量水平。因此，市场势力由进入壁垒决定，而非仅由市场份额决定。
8. Sustainable Prices and the Theory of Market Structure | 可持续价格与市场结构理论
The concept of a sustainable price is central to contestable market theory. A price is sustainable if, given the entrant’s cost structure, no potential entrant can profitably enter the market at that price. In a contestable natural monopoly, the only sustainable price is average cost pricing, because any higher price would generate supernormal profit and invite entry. This insight integrates the analysis of market structure with pricing strategy: the structure of the market, whether monopoly, oligopoly or competition, is endogenous and depends on cost conditions and entry conditions rather than being given exogenously.
可持续价格的概念是可竞争市场理论的核心。所谓可持续价格，是指在给定进入者成本结构的前提下，任何潜在进入者都无法在该价格水平下盈利进入市场。在可竞争的自然垄断行业中，唯一可持续的价格就是平均成本定价，因为任何更高的价格都会产生超额利润并吸引进入。这一洞见将市场结构分析与定价策略融为一体：市场结构，无论是垄断、寡头还是竞争，都是内生的，由成本条件和进入条件决定，而不是外生给定的。
9. Policy Implications for Regulation and Competition | 对监管与竞争政策的政策含义
Contestable market theory has significant implications for government policy. It suggests that policymakers should focus on reducing barriers to entry and exit, rather than breaking up dominant firms. For example, in industries traditionally treated as natural monopolies, such as railways or telecommunications, the government may not need to nationalise the industry or impose detailed price controls if it can ensure that entry is free and sunk costs are low. Deregulation and the removal of licencing requirements are often more effective pro-competition measures than structural intervention.
可竞争市场理论对政府政策具有重要启示。该理论表明，政策制定者应当着重于降低进入和退出壁垒，而非拆分占主导地位的大企业。例如，在传统上被视为自然垄断的行业，如铁路或电信行业，如果政府能够确保进入自由且沉没成本较低，就未必需要国有化整个行业或实施严格的价格管制。放松管制和取消许可要求往往比结构性干预更有效地促进竞争。
10. Real-World Applications and Case Studies | 现实应用与案例研究
Financial markets provide a close real-world approximation to contestability. The rise of digital banking and fintech firms has shown that low-cost entry into the retail banking sector is possible, and this potential entry has pushed traditional banks to lower fees and improve customer service. Similarly, the airline industry is often cited as contestable on long-haul routes: although airport slots may pose a barrier, the development of open-skies agreements and leasing markets enables carriers to enter and exit routes quickly. However, no real market is perfectly contestable; the theory serves as a benchmark against which the competitive pressures facing incumbents can be evaluated.
金融市场提供了接近现实世界可竞争市场的例证。数字银行和金融科技企业的兴起表明，零售银行业的低成本进入是可能的，而这种潜在进入已经促使传统银行降低收费并改善客户服务。同样，航空业在长途航线上经常被视为可竞争市场：尽管机场时刻可能构成壁垒，但开放天空协议和飞机租赁市场的发展使得航空公司能够迅速进入和退出航线。然而，现实中的市场并非完全可竞争；该理论只是提供了一个基准，用于评估在位者所面临的竞争压力。
11. Limitations and Criticisms of Contestable Market Theory | 可竞争市场理论的局限性与批评
Several criticisms of contestable market theory are important for A-Level candidates to understand. First, the assumption of zero sunk costs is extremely unrealistic: most forms of entry, particularly advertising and physical capital, involve some elements that cannot be recovered. Second, the theory assumes that entrants can undercut incumbents quickly, but in many markets consumers face switching costs, brand loyalty and informational asymmetries which slow down the movement of customers. Third, incumbents may engage in strategic entry deterrence, such as limit pricing, product proliferation or aggressive price wars, which the simple contestability model abstracts from. Fourth, contestability focuses heavily on short-run profit opportunities and may underestimate the importance of economies of scale and scope in determining long-run industry structure.
对于A-Level考生而言，理解可竞争市场理论的几个重要批评至关重要。第一，零沉没成本的假设极不现实：大多数进入方式，尤其是广告和实体资本投入，均包含某些无法收回的部分。第二，该理论假设进入者能够迅速压低价格，但在许多市场中，消费者面临转换成本、品牌忠诚和信息不对称，这使客户转移的速度趋缓。第三，在位者可能采取战略性进入阻挠措施，如限制性定价、产品多元化或激进的降价战，这些因素被简单的可竞争模型所忽略。第四，可竞争性理论高度关注短期利润机会，可能低估规模经济和范围经济在决定长期产业结构方面的重要性。
12. Examination Pointers and Common Misunderstandings | 考点提示与常见误区
In CIE A-Level examinations, students are often asked to explain why a profit-maximising monopolist in a perfectly contestable market cannot earn supernormal profit in the long run. A strong answer should explicitly link barriers to entry, particularly sunk costs, with the credibility of the entry threat. It is a common misunderstanding to claim that contestable markets must have many small firms or low fixed costs; these statements are incorrect. Fixed costs can be very high, but as long as they are recoverable, the market remains contestable. Another common error is to treat contestable markets and perfect competition as identical; candidates should emphasise that contestability produces competitive outcomes through the threat of entry, not through the number of firms.
在CIE A-Level考试中，学生经常被要求解释为什么在完全可竞争市场中，追求利润最大化的垄断者长期内无法赚取超额利润。一个有力的答案应当明确地将进入壁垒，尤其是沉没成本，与进入威胁的可信度联系起来。一个常见误区是认为可竞争市场中必须有大量小企业或低固定成本；这些说法都是不正确的。固定成本可以非常高，但只要这些成本能够收回，市场就仍然具备可竞争性。另一个常见错误是将可竞争市场与完全竞争混为一谈；考生应当强调，可竞争性是通过进入威胁而非企业数量来产生竞争性结果的。
Published by TutorHao | Economics Revision Series | aleveler.com
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