📚 IB AQA Economics: Last-Minute Revision Notes | IB AQA 经济：考前冲刺笔记
Welcome to your ultimate last-minute revision guide for IB and AQA Economics. Whether you are sitting Paper 1, 2, or 3, these concise notes cover the most essential micro and macro concepts, key diagrams, and evaluation points to help you secure top marks. Use this resource to refresh your memory on definitions, formulas, and policies before the exam.
欢迎使用 IB 与 AQA 经济学的终极考前冲刺指南。无论你面对的是试卷一、二还是三，这份精炼笔记涵盖了微观与宏观经济最核心的概念、关键图表和评估要点，助你拿下高分。在考前用它快速回顾定义、公式与政策。
1. Scarcity and Choice | 稀缺性与选择
Scarcity is the fundamental economic problem: finite resources cannot satisfy infinite human wants. This forces individuals, firms, and governments to make choices. The opportunity cost of a decision is the next best alternative forgone.
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。某一决策的机会成本是被放弃的次优替代选择。
The production possibility frontier (PPF) illustrates trade-offs and opportunity cost. Points on the curve represent efficient output combinations; points inside show underutilisation of resources. Economic growth shifts the PPF outward, increasing a nation's capacity to produce both goods.
生产可能性边界（PPF）说明了权衡与机会成本。曲线上的点表示有效率的产出组合；曲线内的点表示资源未充分利用。经济增长使 PPF 向外移动，提升一国生产两种商品的能力。
Free goods such as air are abundant with zero opportunity cost, whereas economic goods are scarce and command a price. Rational decision-making involves comparing marginal benefits and marginal costs.
自由物品如空气数量充裕且机会成本为零，而经济物品则是稀缺的并具有价格。理性决策涉及比较边际收益与边际成本。
2. Demand and Supply | 需求与供给
The law of demand states that, ceteris paribus, as price rises, quantity demanded falls, leading to a downward-sloping demand curve. Factors shifting demand include income, tastes, prices of substitutes/complements, and population.
需求定律指出，在其他条件不变的情况下，价格上升，需求量下降，形成向下倾斜的需求曲线。使需求移动的因素包括收入、偏好、替代品/互补品价格和人口。
The law of supply states that as price rises, quantity supplied increases, resulting in an upward-sloping supply curve. Supply shifters include production costs, technology, taxes, subsidies, and the number of sellers.
供给定律指出，价格上升，供给量增加，形成向上倾斜的供给曲线。供给移动因素包括生产成本、技术、税收、补贴和卖方数量。
Market equilibrium occurs where demand equals supply. Disequilibrium leads to excess demand (shortage) or excess supply (surplus) and price adjustments. The price mechanism performs signalling, incentive, and rationing functions in a free market.
市场均衡出现在需求等于供给之处。非均衡导致超额需求（短缺）或超额供给（过剩）并引发价格调整。价格机制在自由市场中发挥着信号、激励和配给的功能。
3. Elasticity | 弹性
Price elasticity of demand (PED) measures responsiveness of quantity demanded to a change in price. Formula:
需求价格弹性（PED）衡量需求量对价格变化的反应程度。公式：
PED = %ΔQd ÷ %ΔP
需求价格弹性 = 需求量变化% ÷ 价格变化%
If |PED| > 1, demand is elastic; if |PED| < 1, inelastic; if |PED| nclude availability of substitutes, necessity vs luxury, proportion of income, and time period.
若 |PED| > 1，需求富有弹性；若 |PED| < 1，缺乏弹性；若 |PED| = 1，为单位弹性。决定因素包括替代品的可得性、必需品与奢侈品、收入占比和时间范围。
| Elasticity Value | Effect on Total Revenue (when price rises) | 弹性值 | 价格上升对总收入的影响 |
|---|---|---|---|
| |PED| > 1 (Elastic) | TR falls | 富有弹性 | 总收入下降 |
| |PED| < 1 (Inelastic) | TR rises | 缺乏弹性 | 总收入上升 |
| |PED| = 1 (Unitary) | TR unchanged | 单位弹性 | 总收入不变 |
Price elasticity of supply (PES) follows similar logic. Key factors: availability of spare capacity, time period, level of stocks, and barriers to entry. Income elasticity of demand (YED) indicates normal goods (YED > 0) vs inferior goods (YED < 0). Cross elasticity of demand (XED) identifies substitutes (XED > 0) and complements (XED < 0).
供给价格弹性（PES）类似。关键因素：闲置产能的可得性、时间范围、库存水平及进入壁垒。收入需求弹性（YED）显示正常商品（YED > 0）与劣等品（YED < 0）。交叉需求弹性（XED）识别替代品（XED > 0）和互补品（XED < 0）。
4. Market Failure | 市场失灵
Market failure occurs when the free market fails to allocate resources efficiently, leading to overproduction or underproduction. Main types: externalities, public goods, information asymmetry, and market power.
当自由市场无法有效配置资源，导致生产过剩或不足时，便出现市场失灵。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 costs to exceed private costs, resulting in overproduction. Diagram: MSC > MPC, welfare loss triangle. Positive externalities (e.g. education) lead to underproduction because MSB > MPB. Public goods are non-rival and non-excludable, leading to the free-rider problem; governments often provide them directly.
负外部性（如污染）使社会成本超过私人成本，导致生产过剩。图示：MSC > MPC，存在福利损失三角。正外部性（如教育）因 MSB > MPB 导致生产不足。公共物品具有非竞争性和非排他性，引发搭便车问题；政府通常直接提供。
Information asymmetry, such as in the market for used cars or healthcare, leads to adverse selection and moral hazard. Monopoly power allows firms to restrict output and raise prices, creating deadweight loss.
信息不对称，如二手车市场或医疗保健，导致逆向选择和道德风险。垄断势力使企业能够限制产量并抬高价格，造成无谓损失。
5. Government Intervention | 政府干预
Governments use indirect taxes (e.g. carbon tax) to internalise negative externalities. A tax shifts the supply curve left, raising price and reducing quantity. Subsidies shift supply right, encouraging consumption of merit goods. Minimum and maximum prices directly control market outcomes.
政府运用间接税（如碳税）将负外部性内部化。税收使供给曲线左移，提高价格并减少数量。补贴使供给曲线右移，鼓励优效品消费。最低和最高限价直接控制市场结果。
Command-and-control regulations (e.g. emissions standards) and tradable pollution permits cap total pollution while allowing firms flexibility. Governments also provide public goods directly or fund merit goods through state provision.
命令与控制型法规（如排放标准）和可交易污染许可证在控制总污染的同时给予企业灵活性。政府还直接提供公共物品或通过国家供给资助优效品。
Evaluation: government failure may arise from inaccurate information, excessive bureaucracy, unintended consequences, and political self-interest. The effectiveness of intervention depends on the elasticities of demand and supply.
评价：信息不准确、过度官僚、意外后果和政治自利可能导致政府失灵。干预的有效性取决于供求弹性。
6. Macroeconomic Objectives | 宏观经济目标
Governments pursue four main objectives: sustainable economic growth, low and stable inflation, low unemployment, and a satisfactory balance of payments. Additional goals include equitable income distribution and environmental sustainability.
政府追求四大目标：可持续经济增长、低而稳定的通胀、低失业率和满意的国际收支。其他目标包括公平收入分配和环境可持续性。
rate = (unemployed ÷ labour force) × 100. Types of unemployment: cyclical, structural, frictional, and seasonal.
经济增长以实际 GDP 的百分比变化衡量。通胀通常以消费者物价指数（CPI）衡量。失业率 = （失业人数 ÷ 劳动力） × 100。失业类型：周期性、结构性、摩擦性和季节性失业。
Trade-offs exist: reducing inflation may raise unemployment (short-run Phillips curve); growth may worsen the current account deficit and deplete natural resources. Policymakers must prioritise according to the economic context.
存在取舍：降低通胀可能推高失业（短期菲利普斯曲线）；经济增长可能恶化经常账户赤字并消耗自然资源。政策制定者需根据经济形势权衡优先目标。
7. Aggregate Demand and Aggregate Supply | 总需求与总供给
: consumption, investment, government spending, net exports. Downward sloping due to: wealth effect, interest rate effect, and exchange rate effect.
AD = C + I + G + (X − M)。构成：消费、投资、政府支出和净出口。向下倾斜原因：财富效应、利率效应和汇率效应。
Short-run aggregate supply (SRAS) is upward sloping because of sticky wages and menu costs. Long-run aggregate supply (LRAS) is vertical at the full-employment level of output, showing an economy's potential output (Yf).
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