📚 IB and OCR Economics: Last-Minute Revision Notes | IB 与 OCR 经济考前冲刺笔记
Welcome to your last‑minute revision notes for IB and OCR Economics. This guide covers the essential concepts, definitions, formulas, and diagrams you need, distilled into bite‑sized paired English–Chinese explanations. Use it to quickly refresh your memory before the exam.
欢迎使用 IB 与 OCR 经济考前冲刺笔记。本文涵盖你所需的核心概念、定义、公式与图表，以精简的英中对照解释呈现。考前用它快速巩固记忆，直击考点。
1. Scarcity, Choice, and Opportunity Cost | 稀缺性、选择与机会成本
The fundamental economic problem is scarcity: finite resources but unlimited human wants. Society must decide what to produce, how to produce, and for whom to produce.
基本经济问题是稀缺性：资源有限而欲望无限。社会必须决定生产什么、如何生产和为谁生产。
Opportunity cost is the value of the next best alternative forgone when a choice is made. Every decision by consumers, firms, or governments involves an opportunity cost.
机会成本是做出选择时所放弃的次优替代品的价值。消费者、企业和政府的每一个决定都包含机会成本。
The Production Possibility Frontier (PPF) shows the maximum output combinations of two goods an economy can produce with full employment of given resources. Points inside the curve indicate inefficiency; points outside are unattainable. An outward shift signals economic growth, while an inward shift suggests decline. A bowed‑out shape reflects increasing opportunity cost.
生产可能性边界 (PPF) 显示一个经济体在充分使用既定资源时所能生产的两种商品的最大组合。曲线内的点表示无效率，曲线外的点无法企及。外移代表经济增长，内移代表经济衰退。向外弯曲的形状反映了递增的机会成本。
2. Demand and Supply Fundamentals | 需求与供给基础
The law of demand states that, ceteris paribus, as the price of a good rises, the quantity demanded falls. This inverse relationship gives the demand curve a negative slope. A change in price causes a movement along the curve, while shifts result from changes in non‑price determinants such as income, tastes, prices of related goods, and expectations.
需求定律指出，在其他条件不变时，商品价格上升，需求量下降。这种负相关关系使需求曲线向下倾斜。价格变化导致沿曲线的移动，而收入、偏好、相关产品价格和预期等非价格因素的变化则导致曲线平移。
The law of supply indicates a positive relationship between price and quantity supplied. Higher prices incentivise firms to produce more. As with demand, a price change moves along the supply curve; shifts are caused by changes in production costs, technology, taxes, subsidies, and the number of sellers.
供给定律表明价格与供给量呈正相关。价格升高激励企业增加产量。与需求类似，价格变动导致沿曲线移动；生产成本、技术、税收、补贴和卖者数量等因素的变化会造成供给曲线平移。
Market equilibrium occurs where quantity demanded equals quantity supplied. At prices above equilibrium, a surplus puts downward pressure on price; below equilibrium, a shortage pushes price upward. The ability of markets to clear depends on the flexibility of prices.
市场均衡出现在需求量等于供给量之处。价格高于均衡时，过剩导致价格下降压力；低于均衡时，短缺推动价格上升。市场出清的能力取决于价格的灵活性。
3. Elasticities: PED, YED, XED, and PES | 弹性：价格弹性、收入弹性、交叉弹性与供给弹性
Price elasticity of demand (PED) measures the responsiveness of quantity demanded to a change in the good’s own price.
PED = %ΔQd / %ΔP
When |PED| > 1, demand is elastic; when |PED| < 1, it is inelastic. Key determinants include availability of substitutes, degree of necessity, time period, and proportion of income spent. Elasticity affects a firm's total revenue and the burden of indirect taxes.
需求价格弹性 (PED) 衡量需求量对该商品自身价格变化的反应程度。|PED| > 1 为富有弹性，|PED| < 1 为缺乏弹性。主要决定因素包括替代品的可获得性、必需程度、时间长短和支出占收入的比例。弹性影响企业的总收益以及间接税的负担。
Income elasticity of demand (YED) = %ΔQd / %ΔY. Normal goods have YED > 0; necessities have 0 < YED < 1, luxuries YED > 1. Inferior goods have YED < 0. YED helps firms forecast sales during the business cycle.
需求收入弹性 (YED) = %ΔQd / %ΔY。正常品的 YED > 0；必需品 0 < YED < 1，奢侈品 YED > 1。低档品的 YED < 0。YED 帮助企业预测商业周期内的销售情况。
Cross elasticity of demand (XED) = %ΔQd of good A / %ΔP of good B. Positive XED indicates substitutes; negative XED indicates complements. The magnitude reveals how closely two goods are related.
需求交叉弹性 (XED) = A 商品需求量变化百分比 / B 商品价格变化百分比。XED 为正表示替代品，为负表示互补品。绝对值大小反映两种商品的紧密程度。
Price elasticity of supply (PES) = %ΔQs / %ΔP. Supply tends to be more elastic in the long run and when producers have spare capacity, when goods can be stored easily, and when production can be switched quickly.
供给价格弹性 (PES) = %ΔQs / %ΔP。长期、存在闲置产能、商品易于储存、生产可快速转换时，供给弹性往往更大。
4. Government Intervention: Taxes, Subsidies, and Price Controls | 政府干预：税收、补贴与价格控制
Indirect taxes (specific or ad valorem) raise production costs, shifting supply left. The tax incidence falls more on consumers when demand is inelastic, and more on producers when demand is elastic. A tax creates a deadweight welfare loss (DWL) because the reduction in quantity traded eliminates some mutually beneficial exchanges.
间接税（从量税或从价税）提高生产成本，使供给曲线左移。当需求缺乏弹性时，消费者承担更多税负；需求富有弹性时，生产者承担更多。税收造成无谓福利损失 (DWL)，因为交易量减少使部分互利交换消失。
Subsidies lower costs of production, shifting supply right. They increase quantity, lower price to consumers, and raise revenue to producers. However, subsidies impose a cost on the government and may encourage inefficiency.
补贴降低生产成本，使供给曲线右移。补贴增加产量、降低消费者价格并提高生产者收入，但同时给政府带来财政负担，并可能鼓励低效率。
Price ceilings (maximum prices) set below equilibrium create persistent shortages and may lead to black markets and non‑price rationing. Price floors (minimum prices) above equilibrium create surpluses; governments may then buy up excess supply, as in agricultural support schemes.
价格上限（最高价格）低于均衡时造成持续短缺，可能引发黑市和非价格配给。价格下限（最低价格）高于均衡时产生过剩；政府可能收购过剩供给，例如农业支持计划。
5. Market Failure and Externalities | 市场失灵与外部性
Market failure occurs when the free market fails to allocate resources efficiently. The main types include externalities, public goods, information asymmetries, and market power.
市场失灵指自由市场无法有效配置资源。主要类型包括外部性、公共品、信息不对称和市场势力。
Negative externalities in production (e.g., pollution) mean marginal social cost (MSC) > marginal private cost (MPC). The free market overproduces. Corrective measures include Pigouvian taxes, tradable permits (cap and trade), and regulation.
生产的负外部性（如污染）意味着边际社会成本 (MSC) 大于边际私人成本 (MPC)，自由市场产量过高。纠正措施包括庇古税、可交易许可证（限量与交易）和直接管制。
Positive externalities in consumption (e.g., education, healthcare) lead to marginal social benefit (MSB) > marginal private benefit (MPB), so the good is under‑consumed. Governments can use subsidies, direct provision, or information campaigns to increase consumption to the socially optimal level.
消费的正外部性（如教育、医疗）使边际社会收益 (MSB) 大于边际私人收益 (MPB)，商品消费不足。政府可通过补贴、直接提供或信息宣传将消费提高到社会最优水平。
Public goods are non‑rivalrous and non‑excludable, leading to the free‑rider problem, so private markets will not supply them in sufficient quantities. Governments typically provide or fund goods like national defence and street lighting.
公共品具有非竞争性和非排他性，导致“搭便车”问题，私人市场供给不足。国防、路灯等通常由政府提供或资助。
6. Macroeconomic Objectives and Key Indicators | 宏观经济目标与关键指标
Governments typically aim for economic growth, low and stable inflation, low unemployment, and a sustainable balance of payments. These objectives may conflict in the short run, creating policy trade‑offs.
政府通常追求经济增长、低且稳定的通胀、低失业以及可持续的国际收支平衡。这些目标在短期内可能互相冲突，形成政策取舍。
Gross Domestic Product (GDP) measures the total value of final goods and services produced within an economy in a given period. It can be calculated via expenditure: GDP = C + I + G + (X − M). Real GDP adjusts for inflation and is the standard measure of growth.
国内生产总值 (GDP) 衡量一个经济体在一定时期内生产的最终商品和服务的总价值。可用支出法计算：GDP = C + I + G + (X − M)。实际 GDP 剔除了通胀因素，是衡量经济增长的标准指标。
Inflation is a sustained increase in the general price level, commonly measured by the Consumer Price Index (CPI). It erodes purchasing power and can create menu costs, shoe‑leather costs, and uncertainty. Unemployment is measured by the labour force survey; types include cyclical, structural, frictional, and seasonal.
通货膨胀是总体价格水平持续上升，常用消费者价格指数 (CPI) 测量。通胀侵蚀购买力，带来菜单成本、鞋底成本和不确定性。失业由劳动力调查衡量；类型包括周期性、结构性、摩擦性和季节性失业。
7. Aggregate Demand and Aggregate Supply | 总需求与总供给
Aggregate demand (AD) is the total spending on domestic goods and services at a given price level. Its components are consumption (C), investment (I), government spending (G), and net exports (X − M). The AD curve slopes downward due to the wealth effect, interest‑rate effect, and international trade effect.
总需求 (AD) 是在给定价格水平下对国内商品和服务的总支出。其构成为消费 (C)、投资 (I)、政府支出 (G) 和净出口 (X − M)。受财富效应、利率效应和国际贸易效应影响，AD 曲线向下倾斜。
Short‑run aggregate supply (SRAS) is upward‑sloping: as the price level rises, firms are willing to supply more because input prices (especially wages) are sticky in the short run. Long‑run aggregate supply (LRAS) is vertical at the full‑employment output, determined by the quantity and quality of factors of production. In the long run, only supply‑side policies can increase potential output.
短期总供给 (SRAS) 向右上方倾斜：价格水平上升时，由于要素价格（特别是工资）在短期具有粘性，企业愿提供更多产出。长期总供给 (LRAS) 在充分就业产出水平处垂直，由生产要素的数量和质量决定。长期中，只有供给侧政策才能增加潜在产出。
Shifts in AD can be caused by changes in confidence, fiscal/monetary policy, or external conditions. Shifts in SRAS can result from changes in input costs, taxes, or supply shocks. The interplay determines the price level and real GDP.
AD 曲线平移源于信心、财政/货币政策或外部环境变化；SRAS 平移源于投入成本、税收变化或供给冲击。两者互动决定了价格水平和实际 GDP。
8. Fiscal and Monetary Policy | 财政与货币政策
Fiscal policy involves government spending and taxation. Expansionary fiscal policy (increased G or lower taxes) boosts AD and is used to close a deflationary gap. Contractionary policy cools an overheating economy. Automatic stabilisers—such as progressive taxes and unemployment benefits—work without active intervention to smooth the business cycle.
财政政策包括政府支出和税收。扩张性财政政策（增加 G 或减税）提高 AD，用于消除通缩缺口；紧缩性政策抑制过热经济。自动稳定器（如累进税和失业救济金）无需主动干预即可平滑经济波动。
Monetary policy is typically controlled by a central bank and focuses on changing the policy interest rate, conducting open‑market operations, or using quantitative easing. Lower interest rates reduce the cost of borrowing and the reward for saving, stimulating C and I. Higher rates dampen spending and control inflation. In a liquidity trap, conventional monetary policy may become ineffective, making QE a preferred tool.
货币政策通常由中央银行操控，重点在于调整政策利率、进行公开市场操作或采用量化宽松 (QE)。降低利率可减少借贷成本与储蓄回报，刺激 C 与 I。提高利率抑制支出、控制通胀。在流动性陷阱中，常规货币政策可能失效，QE 成为重要工具。
Both policies face limitations: time lags, political constraints, crowding out (for fiscal policy), and the need for accurate economic forecasts. Supply‑side policies are often needed to raise long‑term growth without inflation.
两类政策都存在局限性：时滞、政治约束、挤出效应（财政政策），以及对精准经济预测的需求。往往需要供给侧政策才能在无通胀压力下提升长期增长。
9. International Trade and Comparative Advantage | 国际贸易与比较优势
Comparative advantage explains why countries gain from trade even when one nation is absolutely more efficient in producing all goods. A country should specialise in the good for which it has the lowest opportunity cost. The theory assumes no transport costs, constant returns to scale, and perfect factor mobility between domestic industries.
比较优势解释了即使一国在所有商品的生产上都具有绝对优势，贸易仍可让双方获益。一国应专业化生产机会成本最低的商品。该理论假设无运输成本、规模报酬不变、要素在国内行业间完全流动。
Protectionist measures include tariffs, quotas, subsidies to domestic producers, and non‑tariff barriers (e.g., regulations). They typically raise domestic producer surplus but harm consumers and often lead to a net welfare loss. However, they can temporarily protect infant industries, safeguard strategic sectors
Published by TutorHao | IB Economics Revision Series | aleveler.com
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