📚 CIE A-Level Economics: Analysing Oligopoly Firm Behaviour | CIE A-Level 经济：寡头厂商行为分析
An oligopoly is a market structure in which a small number of large firms compete with one another. Because each firm's pricing, output and advertising decisions directly affect its rivals, no single firm can act in isolation. This interdependence shapes every aspect of oligopoly behaviour and lies at the heart of the CIE A-Level Economics syllabus.
寡头是指少数几家大型企业相互竞争的市场结构。由于每家厂商的定价、产量和广告决策都会直接影响其竞争对手，没有任何一家厂商能够孤立行动。这种相互依存关系塑造了寡头行为的各个方面，也是 CIE A-Level 经济课程大纲的核心内容。
1. Key Characteristics of Oligopoly | 寡头的关键特征
Few dominant sellers: the top firms account for a large percentage of market output, often measured by the concentration ratio (e.g. CR5).
少数卖者主导：少数巨头占据市场产出的大部分，常用集中率（如 CR5）衡量。
High barriers to entry: legal, technical or financial obstacles prevent new firms from easily entering the market.
高进入壁垒：法律、技术或财务障碍阻止新厂商轻松进入市场。
Product can be homogeneous (identical) or differentiated, e.g. steel versus branded smartphones.
产品可以是同质的（完全相同），也可以是差异化的，例如钢材与品牌智能手机。
Interdependence: one firm's profit depends not only on its own actions but also on the reactions of rivals.
相互依存：一家厂商的利润不仅取决于自身行为，还取决于对手的反应。
Non-price competition: firms often compete through advertising, branding, research and after-sales service.
非价格竞争：厂商常通过广告、品牌、研发和售后服务进行竞争。
2. Interdependence and Strategic Behaviour | 相互依存与策略行为
In oligopoly every firm must consider the likely responses of its rivals before making a decision. A price cut, for example, may trigger a retaliatory price cut by competitors, leaving all firms worse off. Firms therefore use strategies to maximise their own position while anticipating the actions of others.
在寡头市场中，每家厂商在做决策前都必须考虑对手可能的反应。例如，降价可能引发竞争对手的报复性降价，使所有厂商都受损。因此，厂商会运用策略，在预判他人行动的同时最大化自身地位。
Strategic behaviour includes capacity decisions, price setting, product choice, advertising budgets and even entry deterrence. The outcome depends on the 'game' being played, which is formally analysed using game theory.
策略行为包括产能决策、定价、产品选择、广告预算，甚至进入威慑。结果取决于所“博弈”的规则，这种规则通常用博弈论来正式分析。
3. Introduction to Game Theory | 博弈论入门
Game theory models the strategic interaction between rational decision-makers. In oligopoly, each firm is a 'player' with a set of possible strategies, such as 'cooperate' (hold price) or 'betray' (cut price). Each combination of strategies yields a payoff, usually measured in profits.
博弈论模拟理性决策者之间的策略互动。在寡头中，每家厂商都是“参与者”，拥有一组可选策略，如“合作”（维持价格）或“背叛”（降价）。每种策略组合都会产生一个收益，通常用利润衡量。
A pay-off matrix summarises the outcomes for both players in a two-firm game. It shows how the profit of each firm depends jointly on the choices made by itself and its rival.
收益矩阵总结了双寡头博弈中双方的结局。它展示每家厂商的利润如何共同取决于自己和对手的选择。
4. The Prisoner's Dilemma and Nash Equilibrium | 囚徒困境与纳什均衡
Consider two firms, A and B, each deciding whether to cooperate (hold high price) or betray (offer a discount). Profits in millions are shown below.
考虑厂商 A 和 B，各自决定“合作”（维持高价）还是“背叛”（提供折扣）。利润单位：百万元。
| Firm A \ Firm B | B cooperates 合作 | B betrays 背叛 |
| A cooperates 合作 | A = 8, B = 8Published by TutorHao | A-Level Economics Revision Series | aleveler.com
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