📚 Pre-U OCR Economics: Core Knowledge Points Review | Pre-U OCR 经济：核心知识点梳理
This article provides a comprehensive review of the core knowledge points for the Pre-U OCR Economics syllabus. It covers microeconomic fundamentals, market mechanisms, market failures, macroeconomic objectives and policies, as well as international trade and development. Each section presents key concepts in both English and Chinese, ensuring deep understanding for bilingual learners.
本文为 Pre-U OCR 经济课程提供全面的核心知识点梳理。涵盖微观经济基础、市场机制、市场失灵、宏观经济目标与政策以及国际贸易与发展。每节以中英双语呈现关键概念，确保双语学习者深度理解。
1. The Basic Economic Problem | 基本经济问题
The fundamental economic problem arises from scarcity: limited resources and unlimited wants.
基本经济问题源于稀缺性：有限的资源与无限的欲望。
Scarcity forces individuals, firms, and governments to make choices, which involve opportunity cost.
稀缺性迫使个人、企业和政府做出选择，这涉及机会成本。
Opportunity cost is defined as the value of the next best alternative that is forgone when a decision is made.
机会成本定义为做出决策时放弃的次优选择的价值。
A Production Possibility Frontier (PPF) shows the maximum combinations of two goods an economy can produce with given resources and technology. Points on the curve are efficient, inside are inefficient, and outside are unattainable.
生产可能性边界（PPF）展示一个经济体在给定资源和技术下能生产的两种商品的最大组合。曲线上点有效，内部点低效，外部点不可及。
Economic growth can be shown by an outward shift of the PPF, caused by an increase in resources or technological progress.
经济增长可由 PPF 向外移动表示，由资源增加或技术进步引起。
2. Demand and Supply Analysis | 需求与供给分析
The law of demand states that, ceteris paribus, as price falls, quantity demanded rises, leading to a downward-sloping demand curve.
需求定律指出，其他条件不变，价格下降，需求量上升，导致需求曲线向下倾斜。
Factors shifting the demand curve include changes in income, tastes, prices of related goods (substitutes and complements), population, and expectations.
需求曲线移动的因素包括收入变化、品味、相关商品（替代品和互补品）价格、人口数量和预期。
The law of supply states that, ceteris paribus, as price rises, quantity supplied rises, giving an upward-sloping supply curve.
供给定律指出，其他条件不变，价格上升，供给量上升，供给曲线向上倾斜。
Supply curve shifts result from changes in costs of production, technology, taxes/subsidies, number of sellers, and expectations.
供给曲线移动源于生产成本、技术、税收/补贴、卖家数量和预期的变化。
Market equilibrium occurs where demand equals supply, determining equilibrium price and quantity. Excess supply leads to a price fall; excess demand leads to a price rise.
市场均衡在需求等于供给处达到，决定均衡价格和数量。超额供给导致价格下降；超额需求导致价格上升。
3. Elasticities | 弹性
Price elasticity of demand (PED) measures responsiveness of quantity demanded to a change in price: PED = %ΔQd / %ΔP. It is typically negative, but the absolute value is used.
需求价格弹性（PED）衡量需求量对价格变化的反应程度：PED = 需求量变动百分比 / 价格变动百分比。通常为负，但取绝对值。
If |PED| > 1, demand is elastic; if |PED| < 1, demand is inelastic; perfectly elastic (horizontal) and perfectly inelastic (vertical) are extremes.
若 |PED| > 1，需求富有弹性；若 |PED| < 1，需求缺乏弹性；完全弹性（水平）和完全无弹性（垂直）是极端情况。
Determinants of PED include availability of close substitutes, necessity vs luxury, proportion of income, and time period.
PED 的决定因素有：相近替代品的可得性、必需品与奢侈品、占收入的比例和时间长短。
Income elasticity of demand (YED): YED = %ΔQd / %ΔY. Normal goods have positive YED; luxury goods have YED > 1; inferior goods have negative YED.
需求收入弹性（YED）：YED = 需求量变动百分比 / 收入变动百分比。正常商品 YED 为正；奢侈品 YED > 1；低档品 YED 为负。
Cross-price elasticity of demand (XED): XED = %ΔQd of good A / %ΔP of good B. Positive for substitutes, negative for complements, zero for unrelated goods.
需求交叉价格弹性（XED）：XED = A 商品需求量变动百分比 / B 商品价格变动百分比。替代品为正，互补品为负，无关品为零。
Price elasticity of supply (PES): PES = %ΔQs / %ΔP. Factors include time period, spare capacity, and complexity of production.
供给价格弹性（PES）：PES = 供给量变动百分比 / 价格变动百分比。影响因素有时间长短、闲置产能和生产复杂程度。
4. Market Structure and Efficiency | 市场结构与效率
Perfect competition features many buyers and sellers, homogeneous products, free entry and exit, and perfect information. Firms are price takers. In the long run, normal profit is earned, and allocative and productive efficiency are achieved.
完全竞争特点：众多买家和卖家、同质产品、自由进出、完全信息。企业是价格接受者。长期中仅获正常利润，实现配置效率和生产效率。
Monopoly is a single seller with high barriers to entry. The firm faces a downward-sloping demand curve and can set prices. Monopolies may restrict output and charge higher prices, leading to allocative inefficiency (P > MC) and potentially productive inefficiency.
垄断是单一卖家，进入壁垒高。企业面临向下倾斜的需求曲线，可定价。垄断可能限制产量并提高价格，导致配置无效率（P > MC）和可能的生产无效率。
Oligopoly is a market dominated by a few firms, with interdependence and strategic behaviour. Models include kinked demand curve and game theory. Collusion may lead to cartels.
寡头垄断由少数企业主导，存在相互依赖和策略行为。模型包括弯折需求曲线和博弈论。共谋可能导致卡特尔。
Monopolistic competition involves many firms selling differentiated products, with low barriers. In the long run, firms earn normal profit but have excess capacity and do not achieve productive efficiency.
垄断竞争有许多企业销售差异化产品，壁垒低。长期中企业获正常利润，但存在过剩产能，未达到生产效率。
Allocative efficiency occurs where P = MC; productive efficiency at minimum average cost; dynamic efficiency refers to innovation and improvement over time.
配置效率在 P = MC 时实现；生产效率在最低平均成本处；动态效率指随时间推移的创新和改善。
5. Market Failure and Government Intervention | 市场失灵与政府干预
Market failure occurs when the free market fails to allocate resources efficiently. Key types: externalities, public goods, information asymmetry, and market power.
市场失灵指自由市场不能有效配置资源。主要类型：外部性、公共物品、信息不对称和市场势力。
Negative externalities (e.g. pollution) cause social cost > private cost, leading to overproduction. Positive externalities (e.g. vaccination) cause social benefit > private benefit, leading to underproduction.
负外部性（如污染）导致社会成本 > 私人成本，引起过度生产。正外部性（如疫苗）导致社会收益 > 私人收益，引起生产不足。
Public goods are non-excludable and non-rivalrous, leading to free-rider problem and under-provision by the private sector. Examples: national defence, street lighting.
公共物品具有非排他性和非竞争性，导致搭便车问题和私人部门供给不足。例如：国防、路灯。
Government interventions include indirect taxes (to internalise negative externalities), subsidies (for positive externalities), regulation, provision of public goods, and competition policy.
政府干预措施包括间接税（内化负外部性）、补贴（对正外部性）、监管、提供公共物品和竞争政策。
Government failure can occur when intervention leads to unintended negative consequences, such as information problems, bureaucracy, and political motivations.
当干预导致非预期的负面后果时，可能发生政府失灵，如信息问题、官僚主义和政治动机。
6. Macroeconomic Objectives and National Income | 宏观经济目标与国民收入
Main macroeconomic objectives: sustainable economic growth, low and stable inflation, low unemployment, and a satisfactory balance of payments.
主要宏观经济目标：可持续经济增长、低且稳定的通货膨胀、低失业率以及合意的国际收支平衡。
Gross Domestic Product (GDP) measures the total value of final goods and services produced within a country in a given period. Real GDP adjusts for inflation.
国内生产总值（GDP）衡量一国在一定时期内生产的最终商品和服务的总价值。实际 GDP 剔除通胀影响。
The circular flow of income shows flows between households and firms, with injections (investment, government spending, exports) and leakages (savings, taxes, imports).
收入循环流动展示了家庭和企业之间的流动，包含注入（投资、政府支出、出口）和漏出（储蓄、税收、进口）。
National income can be measured by the output, income, and expenditure approaches, which should be equal in theory.
国民收入可用产出法、收入法和支出法衡量，理论上三者应相等。
7. Aggregate Demand and Aggregate Supply | 总需求与总供给
Aggregate Demand (AD) = C + I + G + (X – M). AD curve slopes downward due to the wealth effect, interest rate effect, and net export effect.
总需求 AD = C + I + G + (X – M)。AD 曲线向下倾斜源于财富效应、利率效应和净出口效应。
Short-run Aggregate Supply (SRAS) is upward-sloping because of sticky wages or misperceptions. Factors shifting SRAS: changes in input prices, productivity, supply shocks.
短期总供给 (SRAS) 向上倾斜，因工资粘性或错觉。SRAS 移动因素：投入品价格变化、生产率、供给冲击。
Long-run Aggregate Supply (LRAS) is vertical at the full-employment level of output (potential GDP). LRAS can shift due to increases in the quantity/quality of factors of production or technology.
长期总供给 (LRAS) 在充分就业产出（潜在 GDP）处垂直。LRAS 移动来源于生产要素量/质的增加或技术进步。
Macroeconomic equilibrium occurs at the intersection of AD and AS. This can be used to analyse output gaps and the price level.
宏观经济均衡在 AD 与 AS 交点实现，可用于分析产出缺口和价格水平。
8. Fiscal and Monetary Policy | 财政与
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