Behaviour of Oligopolistic Firms | 寡头垄断企业的行为

📚 Behaviour of Oligopolistic Firms | 寡头垄断企业的行为

In imperfectly competitive markets, few structures generate as much debate as oligopoly. A small number of large firms dominate the market, and each firm’s actions directly affect rivals’ profits. This article explains the main behavioural models examined in Cambridge A-Level Economics.

在不完全竞争市场中，寡头垄断引发的讨论最为广泛。少数大企业主导市场，每个企业的行动都会直接影响竞争对手的利润。本文解释剑桥 A-Level 经济学考查的主要行为模型。

1. Defining Oligopoly and Key Characteristics | 寡头垄断的定义与关键特征

An oligopoly is a market structure in which a few large firms account for a high proportion of industry output. Concentration is often measured by a concentration ratio, such as the five-firm concentration ratio CR₅ = (sales of top five firms ÷ total market sales) × 100.

寡头垄断是指少数大企业占据行业产出很高比例的市场结构。集中度通常用集中率衡量，例如五企业集中率 CR₅ =（前五名企业销售额 ÷ 市场总销售额）× 100。

Key features include high barriers to entry, product differentiation, interdependence among firms, and the presence of non-price competition. Firms may produce branded consumer goods, vehicles, banking services, or mobile networks.

关键特征包括进入壁垒高、产品差异化、企业之间相互依赖以及存在非价格竞争。企业可能生产品牌消费品、汽车、银行服务或移动网络。

The main characteristics are summarised below.

主要特征总结如下。

Few large firms and high concentration ratio | 少数大企业与高集中率
High barriers to entry and exit | 高进入和退出壁垒
Product differentiation | 产品差异化
Interdependence of firms | 企业相互依赖
Non-price competition | 非价格竞争

2. Interdependence and Strategic Behaviour | 相互依赖与策略行为

Unlike perfect competition or monopoly, an oligopolist cannot set price or output without considering rivals’ likely responses. A price cut by one firm may trigger a price war, while a price rise may cause loss of market share if rivals do not follow.

与完全竞争或垄断不同，寡头企业在制定价格或产量时必须考虑对手的可能反应。一家企业降价可能引发价格战，而提价如果对手不跟进则可能丧失市场份额。

This interdependence makes oligopoly behaviour strategic. Firms choose actions as moves in a game, where payoffs depend on the choices of all players.

这种相互依赖使寡头行为具有策略性。企业把行动视为博弈中的着法，收益取决于所有参与者的选择。

3. The Kinked Demand Curve and Price Rigidity | 弯折需求曲线与价格刚性

The kinked demand curve model assumes that rivals match a price cut but ignore a price rise. Therefore the demand curve is relatively elastic above the current price and relatively inelastic below it.

弯折需求曲线模型假设对手会跟随降价，但不跟随提价。因此在当前价格以上需求曲线相对富有弹性，在当前价格以下相对缺乏弹性。

The kink creates a discontinuous marginal revenue curve. Even if marginal cost changes within the vertical gap of MR, the profit-maximising price stays unchanged. This helps explain price rigidity in oligopoly.

弯折使得边际收益曲线出现垂直间断。即使边际成本在 MR 的垂直缺口内变化，利润最大化价格仍保持不变。这有助于解释寡头市场的价格刚性。

However, the model does not explain how the initial price was determined; it is a starting point for analysing sticky prices rather than a complete theory.

但该模型没有解释初始价格是如何决定的；它只是分析价格粘性的起点，而不是完整理论。

4. Non-price Competition | 非价格竞争

Because price wars can destroy profits, oligopolists often compete through advertising, branding, loyalty schemes, product quality, after-sales service and innovation. These methods aim to increase demand and reduce price elasticity of demand.

由于价格战会摧毁利润，寡头企业常通过广告、品牌、忠诚计划、产品质量、售后服务和创新来竞争。这些方法旨在增加需求并降低需求的价格弹性。

Non-price competition can benefit consumers through better quality and variety, but it can also waste resources on persuasive advertising and create artificial brand loyalty.

非价格竞争可以通过更高的质量和更多品种使消费者受益，但也可能在说服性广告上浪费资源，并制造人为品牌忠诚。

5. Collusion and Cartels | 合谋与卡特尔

Collusion occurs when firms cooperate to reduce uncertainty and increase joint profits. A cartel is a formal agreement to fix prices, restrict output, share markets or coordinate investment.

合谋是指企业合作以减少不确定性并增加联合利润。卡特尔是固定价格、限制产量、瓜分市场或协调投资的正式协议。

A successful cartel acts like a multi-plant monopoly: it restricts industry output to raise price. However, each member has an incentive to cheat by secretly cutting price or exceeding quota.

成功的卡特尔就像多工厂垄断：它限制行业产量以提高价格。然而，每个成员都有作弊动机，比如秘密降价或超配额生产。

Cartels are usually illegal in many countries because they harm consumer welfare, but some international cartels still operate where enforcement is weak.

在许多国家卡特尔通常是非法的，因为它们损害消费者福利，但在执法较弱的地方，一些国际卡特尔仍然存在。

6. Overt and Tacit Collusion | 公开合谋与默契合谋

Overt collusion involves an explicit agreement, often written or verbal, between firms. Tacit collusion arises without direct communication, for example when firms follow an established price leader or avoid aggressive price cuts.

公开合谋涉及企业之间明确的协议，通常是书面或口头协议。默契合谋则无需直接沟通即可产生，例如企业跟随既定的价格领导者，或避免激进降价。

Tacit collusion is harder to detect and prosecute. Firms may signal intentions through public statements about future pricing or capacity, allowing rival firms to coordinate without a formal deal.

默契合谋更难发现和起诉。企业可以通过关于未来定价或产能的公开声明释放信号，使竞争对手无需正式协议就能协调行动。

In many exam questions, students must distinguish between these two forms and explain why tacit collusion is more common in concentrated markets.

在许多考试题目中，学生必须区分这两种形式，并解释为何默契合谋在集中度高的市场中更常见。

7. Price Leadership | 价格领导

Price leadership is a form of tacit collusion. A dominant firm, often the largest or lowest-cost producer, changes its price and other firms follow. Price changes may be announced through trade journals, press releases or earnings calls.

价格领导是默契合谋的一种形式。占主导地位的企业，通常是规模最大或成本最低的生产者，改变价格，其他企业跟随。价格变动可能通过行业刊物、新闻稿或财报电话会议公布。

Barometric price leadership occurs when a firm is not dominant but is trusted as a reliable indicator of market conditions. In contrast, dominant-firm price leadership reflects market power.

晴雨表式价格领导是指一家企业并不占主导地位，但被信赖为市场状况的可靠指标。相比之下，主导企业价格领导反映的是市场势力。

8. Game Theory and the Prisoner’s Dilemma | 博弈论与囚徒困境

Game theory models strategic interdependence. The prisoner’s dilemma is a classic game in which two suspects would be better off cooperating by staying silent, but each has a dominant strategy to confess, leading to a worse joint outcome.

博弈论为策略性相互依赖建模。囚徒困境是一个经典博弈：两名嫌疑人若都保持沉默会更好，但每人都有招供的占优策略，导致更差的共同结果。

In an oligopoly, two firms may each choose between a high price and a low price. If both choose high price, they earn healthy profits. If both choose low price, they compete aggressively and earn lower profits. But each firm has an incentive to undercut.

在寡头市场中，两家企业可能各自在高价和低价之间选择。若都选高价，它们获得可观利润。若都选低价，它们激烈竞争，利润更低。但每家企业都有降价的动机。

This tension explains why collusion is unstable, even when firms know cooperation maximises joint profit.

这种紧张关系解释了为何合谋不稳定，即使企业知道合作会使联合利润最大化。

9. Nash Equilibrium and Dominant Strategies | 纳什均衡与占优策略

A dominant strategy is one that gives a player the best payoff regardless of the rival’s choice. A Nash equilibrium occurs when each player chooses the best strategy given the strategies chosen by others, and no one has an incentive to change unilaterally.

占优策略是指无论对手如何选择，都能给参与者带来最佳收益的策略。纳什均衡是指每个参与者都根据其他参与者的策略选择了最佳策略，且没有人有单方面改变的动机。

In a one-shot prisoner’s dilemma, the dominant strategy equilibrium is low price, low price. This Nash equilibrium is not Pareto efficient because both firms could be better off with high price, high price.

在一次性囚徒困境中，占优策略均衡是低价、低价。这一纳什均衡不是帕累托有效的，因为两家企业都选择高价、高价时会更好。

In repeated games, cooperation may be sustained by strategies such as tit-for-tat, where a firm starts by cooperating and then copies the rival’s previous move. This can support tacit collusion over time.

在重复博弈中，合作可以通过以牙还牙等策略维持：企业先合作，然后复制对手上一轮的行动。这可以长期支持默契合谋。

A simple pay-off matrix can illustrate these concepts. The numbers show profit in £ million for Firm A and Firm B.

一个简单的收益矩阵可以说明这些概念。数字表示 A 企业和 B 企业的利润，单位百万英镑。

Firm A \ Firm B	B sets high price	B sets low price
A sets high price	A 10, B 10	A 4, B 12
A sets low price	A 12, B 4	A 6, B 6

In this matrix, low price is a dominant strategy for both firms because 12 > 10 and 6 > 4

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Behaviour of Oligopolistic Firms | 寡头垄断企业的行为