📚 Oligopoly: Strategic Interdependence and Market Power | 寡头垄断：战略相互依赖与市场势力
Oligopoly is a market structure in which a small number of large firms dominate the industry. Unlike perfect competition or monopoly, the key feature is strategic interdependence: each firm must consider the likely reactions of rivals before changing price, output, advertising, or product design. For Cambridge A-Level Economics, this topic emphasises the kinked demand curve, game theory, collusion, and evaluation of market outcomes.
寡头垄断是一种少数大企业主导行业的市场结构。与完全竞争或垄断不同，其核心特征是战略相互依赖：每家厂商在改变价格、产量、广告或产品设计之前，都必须考虑竞争对手的可能反应。剑桥 A-Level 经济学对该主题的考查重点包括拗折需求曲线、博弈论、合谋以及对市场结果的评价。
1. Defining Oligopoly | 寡头垄断的定义
An oligopoly exists when a few firms account for a large share of total market output. The market may be dominated by as few as two firms (duopoly) or by several large firms. High barriers to entry, such as economies of scale, brand loyalty, and legal restrictions, protect incumbent firms.
当少数几家企业占据市场总产出的很大份额时，就形成了寡头垄断。市场可能由两家企业（双头垄断）或几家大企业主导。规模经济、品牌忠诚度和法律限制等高进入壁垒保护了现有企业。
Products can be homogeneous, such as steel or cement, or differentiated, such as cars, banking, and mobile phones. The defining analytical feature is mutual interdependence: a price cut by one firm can trigger a price war, while a price rise may be ignored.
产品可以是同质的，如钢铁或水泥；也可以是差异化的，如汽车、银行和移动电话。分析上的决定性特征是相互依赖：一家厂商降价会引发价格战，而涨价则可能被对手忽视。
2. Concentration Ratios | 集中度比率
The concentration ratio measures the combined market share of the largest n firms, usually the 3-firm or 5-firm ratio. A high concentration ratio, for example CR5 above 60%, indicates an oligopolistic market.
集中度比率衡量最大的 n 家企业的合计市场份额，通常使用 3 厂商或 5 厂商集中度。较高的集中度比率，例如 CR5 超过 60%，表明市场属于寡头垄断。
However, concentration ratios have limitations. They do not show whether the market is contestable, whether products are differentiated, or how market power is distributed among the top firms.
但集中度比率也有局限。它无法说明市场是否具有可竞争性、产品是否差异化，也无法反映头部企业之间市场势力的分布情况。
3. Mutual Interdependence and Strategic Behaviour | 相互依赖与战略行为
Mutual interdependence means that the profits of one firm depend not only on its own decisions but also on the reactions of rivals. This creates strategic behaviour: firms may signal intentions, build reputations, or use trigger strategies.
相互依赖意味着一家厂商的利润不仅取决于自身决策，还取决于竞争对手的反应。这产生了战略行为：厂商可能会传递意图、建立声誉或使用触发策略。
Because direct price competition can reduce industry profit, oligopolists often prefer stable prices and non-price rivalry. This explains why prices in many oligopolistic markets, such as petrol retailing or banking, change infrequently.
由于直接的价格竞争会降低行业利润，寡头企业往往更倾向于稳定的价格和非价格竞争。这解释了为什么许多寡头市场（如汽油零售或银行业）的价格变化并不频繁。
4. The Kinked Demand Curve and Price Rigidity | 拗折需求曲线与价格刚性
The kinked demand curve model assumes that rivals will match a price cut but will not match a price rise. Therefore the demand curve facing the firm is relatively elastic above the existing price and relatively inelastic below it.
拗折需求曲线模型假设竞争对手会跟随降价，但不会跟随涨价。因此，厂商面临的需求曲线在现行价格之上相对富有弹性，在现行价格之下相对缺乏弹性。
The kink creates a vertical discontinuity in the marginal revenue curve. As a result, moderate shifts in marginal cost may leave the profit-maximising price unchanged, producing price rigidity.
拗折使边际收益曲线出现垂直断开。因此，边际成本的适度变动可能不会改变利润最大化价格，从而产生价格刚性。
Critics argue that the model explains price stability but does not explain how the initial price is determined. It also assumes that rivals always match price cuts, which is not universally true.
批评者认为该模型解释了价格稳定，但没有解释初始价格是如何形成的。它还假设竞争对手总是跟随降价，这一假设并不普遍成立。
5. Non-Price Competition | 非价格竞争
Since price wars can be mutually destructive, oligopolists often compete through advertising, branding, product quality, loyalty schemes, and after-sales service. These methods can increase demand and build barriers to entry without directly cutting price.
由于价格战可能两败俱伤，寡头企业往往通过广告、品牌、产品质量、忠诚度计划和售后服务进行竞争。这些方式可以在不直接降价的情况下增加需求并建立进入壁垒。
Non-price competition can benefit consumers through innovation and variety, but excessive advertising may be wasteful and can raise costs. Firms may also use persuasive advertising to reduce price elasticity of demand.
非价格竞争可以通过创新和产品多样性使消费者受益，但过度的广告可能是浪费性的并推高成本。厂商还可能利用劝说性广告来降低需求的价格弹性。
6. Game Theory and the Prisoner’s Dilemma | 博弈论与囚徒困境
Game theory analyses strategic interactions where each firm’s best choice depends on what the other does. The prisoner’s dilemma shows why rational firms may not cooperate even when cooperation would raise joint profits.
博弈论分析战略互动，即每家企业的最优选择取决于对手的行动。囚徒困境表明，即使合作能提高联合利润，理性的企业也可能不合作。
Consider a simplified pricing game between Firm A and Firm B. The table shows profits in £ millions for combinations of high and low prices.
考虑企业 A 和企业 B 之间的一个简化定价博弈。下表显示了高价和低价组合下的利润，单位为百万英镑。
| Firm B: High price | Firm B: Low price | |
| Firm A: High price | (10, 10) | (2, 14) |
| Firm A: Low price | (14, 2) | (5, 5) |
In the payoff matrix above, if both firms charge a high price they earn £10m each. If one firm undercuts by charging a low price while the other remains high, the undercutter earns £14m and the rival earns £2m. The dominant strategy for each firm is to charge a low price, giving the Nash equilibrium of (£5m, £5m), which is worse for both than mutual high pricing.
在上面的支付矩阵中，如果两家厂商都制定高价，各赚 1000 万英镑。如果一家降价而另一家维持高价，降价者赚 1400 万英镑，对手赚 200 万英镑。每家厂商的占优策略都是降价，形成纳什均衡（500 万英镑，500 万英镑），这对双方而言都比共同维持高价更差。
The prisoner’s dilemma helps explain price wars, advertising wars, and the incentive to cheat on collusive agreements. However, in repeated games, cooperation may be sustained by tit-for-tat strategies and the threat of punishment.
囚徒困境有助于解释价格战、广告战以及背叛合谋协议的激励。但在重复博弈中，以牙还牙策略和惩罚威胁可能维持合作。
7. Collusion and Cartels | 合谋与卡特尔
Collusion occurs when firms coordinate prices, output, or market sharing to increase joint profits. Formal collusion creates a cartel, such as OPEC, while tacit collusion involves unspoken coordination, such as following a price leader.
合谋是指厂商协调价格、产量或市场份额以增加联合利润。正式合谋形成卡特尔，如 OPEC；默契合谋则是一种心照不宣的协调，例如跟随价格领导者。
Cartels aim to restrict output and raise price above the competitive level. They are unstable because each member has an incentive to cheat by secretly lowering price or producing extra output. Cheating can trigger price wars and collapse the cartel.
卡特尔旨在限制产量并将价格提高到竞争水平之上。卡特尔并不稳定，因为每个成员都有作弊激励，暗中降价或超额生产。作弊会引发价格战并导致卡特尔瓦解。
Collusion is usually illegal in many countries, but tacit collusion is harder to detect and prosecute because there is no explicit agreement.
在许多国家，合谋通常是非法的，但默契合谋更难被察觉和起诉，因为没有明确的协议。
8. Price Leadership | 价格领导
Price leadership is a form of tacit collusion in which a dominant firm sets the price and smaller rivals follow. It allows firms to achieve coordinated price increases without explicit communication.
价格领导是默契合谋的一种形式，由主导企业设定价格，较小的竞争对手跟随。它使企业无需明确沟通就能实现协调涨价。
There are two main types: dominant-firm price leadership, where one large low-cost firm leads, and barometric price leadership, where a respected firm acts as a barometer of market conditions. Price leadership reduces the risk of price wars but may still be investigated by competition authorities.
主要有两类：主导厂商价格领导，由一家大型低成本企业引领；以及气压计式价格领导，由一家受尊重的企业充当市场状况的晴雨表。价格领导降低了价格战风险，但仍可能受到竞争主管机构的调查。
9. Evaluation of Oligopoly | 寡头垄断的评价
Oligopoly can lead to allocative inefficiency because price is often above marginal cost, resulting in a deadweight loss. Productive inefficiency may also exist if firms lack competitive pressure to minimise costs, though economies of scale can reduce average costs.
寡头垄断可能导致配置无效率，因为价格通常高于边际成本，造成无谓损失。如果厂商缺乏最小化成本的竞争压力，也可能存在生产无效率，尽管规模经济可以降低平均成本。
However, oligopolists may use supernormal profits to fund research and development, yielding dynamic efficiency, product innovation, and better quality. This is an important trade-off: some market power may be necessary to reward innovation.
但寡头企业可能利用超额利润资助研发，从而带来动态效率、产品创新和更高质量。这是一个重要的权衡：一定的市场势力可能是奖励创新所必需的。
Consumers may benefit from stability, variety, and innovation, but may suffer from higher prices, restricted choice, and possible collusion. The overall welfare effect depends on contestability, regulation, and the strength of non-price competition.
消费者可能受益于价格稳定、产品多样性和创新，但也可能因高价、选择受限和潜在合谋而受损。总体福利效果取决于市场的可竞争性、监管力度以及非价格竞争的强度。
10. Competition Policy and Regulation | 竞争政策与监管
Competition authorities, such as the UK Competition and Markets Authority (CMA) and the European Commission, aim to prevent anti-competitive behaviour. They can impose fines on cartels, block mergers that substantially lessen competition, and investigate abuse of a dominant position.
竞争主管机构，如英国竞争与市场管理局（CMA）和欧盟委员会，旨在防止反竞争行为。它们可以对卡特尔处以罚款，阻止实质性削弱竞争的合并，并调查滥用市场支配地位的行为。
Policy tools include price caps, windfall taxes, and measures to increase market contestability, such as reducing entry barriers and improving information. However, regulation can be costly, and authorities may struggle to prove tacit collusion.
政策工具包括价格上限、暴利税以及提高市场可竞争性的措施，如降低进入壁垒和改善信息。但监管可能成本高昂，监管机构也可能难以证明默契合谋。
Published by TutorHao | Economics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导