📚 Year 12 OCR Economics: Core Knowledge Review | Year 12 OCR 经济：核心知识点梳理
Year 12 OCR Economics builds the essential foundation for understanding how markets and economies work. This review covers the core microeconomic and macroeconomic concepts you need to master, from scarcity and market equilibrium to aggregate demand and international trade. Each topic is presented with clear explanations and real-world applications to help you succeed in your exams.
Year 12 OCR 经济课程为你理解市场和经济运行打下坚实基础。本篇梳理涵盖了必须掌握的微观与宏观经济核心概念，从稀缺性、市场均衡到总需求与国际贸易。每个主题都配有清晰的解释和现实世界应用，帮助你更好地应对考试。
1. Scarcity, Choice and Opportunity Cost | 稀缺性、选择与机会成本
Scarcity is the fundamental economic problem: limited resources cannot satisfy all unlimited human wants. This compels individuals, firms, and governments to make choices.
稀缺性是基本的经济问题：有限的资源无法满足无限的人类欲望。这迫使个人、企业和政府做出选择。
Opportunity cost is the value of the next best alternative forgone when a decision is made. It is a crucial concept because every choice involves a trade-off.
机会成本是做出决定时所放弃的次优替代品的价值。这是一个关键概念，因为每个选择都涉及权衡取舍。
Economic agents must answer three basic questions: what to produce, how to produce, and for whom to produce. These questions arise directly from the problem of scarcity.
经济主体必须回答三个基本问题：生产什么、如何生产、为谁生产。这些问题直接源自稀缺性。
2. Production Possibility Frontiers (PPF) | 生产可能性边界
A Production Possibility Frontier shows the maximum possible output combinations of two goods or services an economy can produce with all resources fully and efficiently employed. Points on the curve are efficient, points inside are inefficient, and points outside are currently unattainable.
生产可能性边界显示了在资源被充分利用和有效配置时，一个经济体所能生产的两种商品或服务的最大组合。曲线上的点表示有效率，曲线内的点表示无效率，曲线外的点目前无法达到。
The shape of a PPF is typically concave to the origin, reflecting increasing opportunity cost as resources are not equally suited to producing both goods. A shift outward of the PPF represents economic growth, caused by an increase in the quantity or quality of resources.
PPF 通常凹向原点，这反映了机会成本递增，因为资源并非同样适用于生产两种产品。PPF 向外移动代表经济增长，它是由资源数量或质量的提升引起的。
Capital goods versus consumer goods: a choice to produce more capital goods today can shift the PPF outward further in the future, boosting long-run growth. This illustrates the trade-off between present consumption and future prosperity.
资本品与消费品：如今生产更多资本品的选择可能在未来使 PPF 进一步向外移动，从而促进长期增长。这说明了当前消费与未来繁荣之间的权衡。
3. Demand, Supply and Market Equilibrium | 需求、供给与市场均衡
The law of demand states that, ceteris paribus, as the price of a good rises, quantity demanded falls; as price falls, quantity demanded rises. This inverse relationship is represented by a downward-sloping demand curve.
需求定律指出，在其他条件不变的情况下，商品价格上升，需求量下降；价格下降，需求量上升。这种反向关系表现为一条向下倾斜的需求曲线。
The law of supply states that, ceteris paribus, as price rises, quantity supplied rises; as price falls, quantity supplied falls. The supply curve slopes upward because higher prices incentivise producers to offer more.
供给定律指出，在其他条件不变的情况下，价格上升，供给量增加；价格下降，供给量减少。供给曲线向上倾斜，因为更高的价格激励生产者提供更多商品。
Market equilibrium occurs where quantity demanded equals quantity supplied, determining the equilibrium price and quantity. Any price above equilibrium creates a surplus, putting downward pressure on price; any price below creates a shortage, pushing price upward.
市场均衡出现在需求量等于供给量时，决定了均衡价格和均衡数量。任何高于均衡的价格都会造成过剩，给价格带来下行压力；任何低于均衡的价格都会造成短缺，推动价格上升。
The price mechanism has three key functions: signalling (prices convey information about scarcity), incentive (prices motivate producers and consumers to change behaviour), and rationing (prices allocate scarce resources to those willing and able to pay).
价格机制具有三个关键功能：信号功能（价格传递稀缺信息）、激励功能（价格促使生产者和消费者改变行为）和配给功能（价格将稀缺资源配置给愿意且能够支付的人）。
4. Elasticity | 弹性
Price elasticity of demand (PED) measures the responsiveness of quantity demanded to a change in price. The formula is:
需求价格弹性（PED）衡量需求量对价格变化的反应程度。计算公式如下：
PED = % change in quantity demanded / % change in price (or %ΔQd / %ΔP)
1, demand is unit elastic. Determinants include the availability of substitutes, the proportion of income spent, and whether the good is a necessity or luxury.
若 PED > 1，需求富有弹性；若 PED < 1，需求缺乏弹性；若 PED = 1，需求为单位弹性。决定因素包括替代品的可获得性、支出占收入的比例，以及该商品是必需品还是奢侈品。
Income elasticity of demand (YED) measures how demand responds to changes in income. Normal goods have positive YED; luxury goods have YED > 1; inferior goods have negative YED. Cross elasticity of demand (XED) shows how demand for one good responds to price changes of another: positive for substitutes, negative for complements.
需求收入弹性（YED）衡量需求对收入变化的反应。正常品的 YED 为正；奢侈品 YED > 1；劣等品 YED 为负。需求交叉弹性（XED）显示一种商品的需求对另一种商品价格变化的反应：替代品为正，互补品为负。
Price elasticity of supply (PES) measures how quantity supplied responds to price changes. Its determinants include the time period, spare production capacity, and the ease of storing inventory. In the momentary period, supply is often perfectly inelastic; in the long run, supply becomes more elastic.
供给价格弹性（PES）衡量供给量对价格变化的反应。决定因素包括时间周期、闲置生产能力和库存的难易程度。在瞬时阶段，供给往往完全无弹性；从长期来看，供给会变得更具弹性。
5. Market Failure | 市场失灵
Market failure occurs when the free market, without government intervention, leads to an inefficient allocation of resources and a net welfare loss. Four main causes are externalities, public goods, information asymmetry, and monopoly power.
市场失灵是指在没有政府干预的情况下，自由市场导致资源配置无效率并出现净福利损失。四个主要原因包括外部性、公共物品、信息不对称和垄断势力。
Externalities are third-party spillover effects from production or consumption. A negative production externality means the social cost exceeds the private cost, leading to overproduction. A positive consumption externality means the social benefit exceeds the private benefit, leading to under-consumption.
外部性是生产或消费对第三方造成的溢出效应。负生产外部性意味着社会成本超过私人成本，导致过度生产。正消费外部性意味着社会收益超过私人收益，导致消费不足。
Public goods are non-rival (one person’s consumption does not reduce availability to others) and non-excludable (impossible to prevent non-payers from benefiting). These features lead to the free-rider problem, so markets will under-provide or not provide them at all.
公共物品具有非竞争性（一个人的消费不会减少他人可用的数量）和非排他性（无法阻止未付费者受益）。这些特征导致“搭便车”问题，因此市场会供给不足或根本不提供。
Information asymmetry means one party in a transaction has more or better information than the other, leading to problems like adverse selection and moral hazard. Monopoly power allows a dominant firm to restrict output and raise prices above marginal cost, creating a deadweight loss.
信息不对称指交易中的一方拥有比另一方更多或更好的信息，从而引发逆向选择和道德风险等问题。垄断势力使主导企业能够限制产出并将价格定在边际成本之上，从而造成无谓损失。
6. Government Intervention in Markets | 政府对市场的干预
Governments use indirect taxes to internalise negative externalities: an ad valorem tax is a percentage of the price, while a specific tax is a fixed amount per unit. The tax incidence depends on the relative PED and PES.
政府使用间接税将负外部性内部化：从价税按价格的一定百分比征收，而从量税按每单位固定金额征收。税收负担取决于相对的需求价格弹性和供给价格弹性。
Subsidies are payments to producers that lower production costs and increase supply. They can correct positive externalities, e.g. subsidies for education or renewable energy. However, they carry an opportunity cost and can lead to government failure if poorly targeted.
补贴是支付给生产者以降低其生产成本、增加供给的款项。它们可以纠正正外部性，例如对教育或可再生能源的补贴。然而，补贴有机会成本，并且如果目标不精准，可能导致政府失灵。
Maximum prices (ceilings) set below equilibrium create shortages and can lead to black markets. Minimum prices (floors) set above equilibrium create surpluses, and governments may have to purchase the excess supply. Governments also use regulation, such as bans or compulsory standards, and provision of information to correct market failures.
最高限价（价格上限）设定在均衡价格之下会造成短缺，并可能催生黑市。最低限价（价格下限）设定在均衡价格之上会造成过剩，政府可能不得不购买过剩的供给。政府还使用管制（如禁令或强制性标准）以及提供信息来纠正市场失灵。
Government failure may occur when intervention leads to unintended consequences that outweigh the benefits, such as regulatory capture, excessive administrative costs, or distorted incentives.
当干预带来的意外后果超过其益处时，就可能发生政府失灵，例如监管俘获、过高的行政成本或扭曲的激励。
7. Macroeconomic Objectives and Indicators | 宏观经济目标与指标
The main macroeconomic objectives are sustainable economic growth, low unemployment, price stability (low inflation), and a stable balance of payments on current account. Governments may also target equitable income distribution and environmental sustainability.
主要的宏观经济目标包括可持续的经济增长、低失业、物价稳定（低通胀）和经常账户的国际收支平衡。政府可能还会将公平的收入分配和环境可持续性作为目标。
Economic growth is measured by the percentage change in real GDP. Real GDP adjusts nominal GDP for inflation, so it reflects changes in the actual volume of output. A positive growth rate indicates an expanding economy.
经济增长通过实际 GDP 的百分比变化来衡量。实际 GDP 根据通胀对名义 GDP 进行调整，因此反映的是实际产出量的变化。正增长率表明经济在扩张。
Inflation is a sustained increase in the general price level. In the UK, it is measured by the Consumer Price Index (CPI) and CPIH. Demand-pull inflation is caused by excess AD, while cost-push inflation arises from rising production costs.
通货膨胀是总体物价水平的持续上升。在英国，通胀通过消费者物价指数（CPI）和包含住房成本的 CPIH 来衡量。需求拉上型通胀由过度总需求引起，而成本推动型通胀则源于生产成本的上升。
Unemployment is measured by the Claimant Count and the Labour Force Survey. Types of unemployment include cyclical (caused by a lack of AD), frictional (between jobs), structural (mismatch of skills), and seasonal. High unemployment represents a waste of resources and lost output.
失业通过申领人数统计和劳动力调查来衡量。失业类型包括周期性失业（总需求不足引起）、摩擦性失业（换工作期间）、结构性失业（技能不匹配）和季节性失业。高失业率意味着资源浪费和产出损失。
8. Aggregate Demand and Aggregate Supply | 总需求与总供给
Aggregate demand (AD) is the total spending on domestic goods and services. Its components are: C (consumption), I (investment), G (government spending), and (X–M) net exports. The AD curve slopes downward due to the wealth effect, interest rate effect, and international trade effect.
总需求（AD）是指对国内商品和服务的总支出。其组成包括：消费（C）、投资（I）、政府支出（G）和净出口（X–M）。由于财富效应、利率效应和国际贸易效应，AD 曲线向下倾斜。
Short-run aggregate supply (SRAS) shows the relationship between the price level and the quantity of real GDP supplied, assuming some input prices are sticky. Cost increases (e.g. higher energy prices) shift SRAS left; productivity improvements shift it right.
短期总供给（SRAS）显示了在部分生产要素价格具有粘性的情况下，价格水平与实际 GDP 供给量之间的关系。成本上升（例如能源价格上涨）使 SRAS 向左移动；生产率提高使其向右移动。
Long-run aggregate supply (LRAS) represents the economy's potential output at full employment. The classical/new classical LRAS is vertical because in the long run wages and prices are fully flexible. The Keynesian LRAS curve has three distinct segments: perfectly elastic during deep recession, upward-sloping as the economy approaches capacity, and vertical at full capacity.
长期总供给（LRAS）代表经济在充分就业时的潜在产出。古典/新古典学派的 LRAS 是垂直的，因为在长期内工资和价格完全弹性。凯恩斯主义的 LRAS 曲线有三个明显阶段：深度衰退时完全弹性，经济接近产能时向上倾斜，达到充分产能时垂直。
Macroeconomic equilibrium occurs where AD equals SRAS. A negative output gap exists when actual GDP is below potential; a positive output gap exists when actual GDP exceeds potential. Supply-side shocks can cause stagflation: a simultaneous rise in price level and fall in output.
宏观经济均衡出现在 AD 等于 SRAS 时。当实际 GDP 低于潜在产出时，存在负产出缺口；当实际 GDP 高于潜在产出时，存在正产出缺口。供给端冲击可能引起滞胀：价格水平上升而产出同时下降。
9. Macroeconomic Policy | 宏观经济政策
Fiscal policy involves changes in government spending and taxation to influence AD. Expansionary fiscal policy (e.g. tax cuts, increased G) boosts AD; contractionary policy reduces it. Automatic stabilisers, like progressive taxation and welfare benefits, work without active government decisions.
财政政策通过改变政府支出和税收来影响总需求。扩张性财政政策（如减税、增加政府支出）会刺激 AD；紧缩性政策则会抑制 AD。自动稳定器，如累进税和福利津贴，无需积极的政府决策便能发挥作用。
Monetary policy, conducted by the Bank of England in the UK, uses changes in the official interest rate (Bank Rate) and quantitative easing (QE) to influence AD and inflation. Lower interest rates reduce the cost of borrowing and encourage consumption and investment.
在英国，货币政策由英格兰银行执行，运用官方利率（基准利率）和量化宽松（QE）影响 AD 和通胀。降低利率可以减少借贷成本，鼓励消费和投资。
Supply-side policies aim to increase the productive capacity of the economy by shifting LRAS rightwards. Market-based policies include tax reforms, deregulation, and privatisation. Interventionist policies include investment in education, training, and infrastructure.
供给侧政策旨在通过将 LRAS 向右移动来提高经济的生产能力。市场化政策包括税制改革、放松管制和私有化。干预主义政策则包括对教育、培训和基础设施的投资。
Policy conflicts can arise: expansionary fiscal policy to reduce unemployment may cause higher inflation and worsen the trade balance. Supply-side policies take time to take effect and may require significant public spending.
政策目标之间可能发生冲突：旨在降低失业的扩张性财政政策可能会加剧通胀并使贸易平衡恶化。供给侧政策见效较慢，并可能需要大量公共支出。
10. International Trade | 国际贸易
International trade allows countries to specialise according to comparative advantage: a country should specialise in producing the good with the lowest opportunity cost, relative to other goods. This increases global output and allows gains from trade for all parties.
国际贸易使各国能够根据比较优势进行专业化生产：一国应当专业化生产其机会成本最低的商品（相对于其他商品而言）。这会增加全球产出，并使所有参与方都能从贸易中获益。
index of export prices / index of import prices) × 100. An improvement means a country can
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