📚 AS AQA Economics: Quick Reference Handbook of Formulas and Theorems | AS AQA 经济：公式定理速查手册
This handbook provides a concise summary of the essential formulas, theorems and key relationships required for the AS AQA Economics specification. It covers both microeconomic and macroeconomic principles, enabling students to revise and apply quantitative and theoretical concepts effectively. All definitions are aligned with the AQA AS curriculum, ensuring exam-relevant coverage of elasticity, costs, market structures, macroeconomic aggregates and more.
本手册简要汇总了AS AQA经济学课程中必备的公式、定理与核心关系，涵盖微观与宏观经济学原理，帮助学生高效复习并应用定量与理论概念。所有定义均符合AQA AS教学大纲，确保覆盖弹性、成本、市场结构、宏观经济总量等考试重点内容。
1. Price Elasticity of Demand (PED) | 需求价格弹性
PED measures the responsiveness of quantity demanded to a change in price. It is calculated as the percentage change in quantity demanded divided by the percentage change in price. The sign is normally negative, but the absolute value is used to classify elasticity.
需求价格弹性衡量需求量对价格变动的反应程度，计算公式为需求量变动的百分比除以价格变动的百分比。符号通常为负，但在分类时使用绝对值。
PED = %ΔQd ÷ %ΔP
需求价格弹性 = 需求量变动百分比 ÷ 价格变动百分比
Values indicate: |PED| > 1 → elastic; |PED| < 1 → inelastic; |PED| = 1 → unit elastic; |PED| = 0 → perfectly inelastic; |PED| → ∞ → perfectly elastic.
数值含义：|PED| > 1 → 富有弹性；|PED| < 1 → 缺乏弹性；|PED| = 1 → 单位弹性；|PED| = 0 → 完全无弹性；|PED| → ∞ → 完全弹性。
Key determinants: number and closeness of substitutes, necessity vs luxury, proportion of income, time period.
主要决定因素：替代品的数量与相似程度、必需品与奢侈品、支出占收入的比例、时间长短。
2. Income Elasticity of Demand (YED) | 需求收入弹性
YED measures the responsiveness of demand to a change in income. It is the percentage change in quantity demanded divided by the percentage change in real income.
需求收入弹性衡量需求对收入变动的反应程度，即需求量变动百分比除以实际收入变动百分比。
YED = %ΔQd ÷ %ΔY
需求收入弹性 = 需求量变动百分比 ÷ 收入变动百分比
Interpretation: YED > 0 → normal good; YED < 0 → inferior good; YED > 1 → luxury good (income-elastic); 0 < YED < 1 → necessity (income-inelastic).
解读：YED > 0 → 正常品；YED < 0 → 低档品；YED > 1 → 奢侈品（富有收入弹性）；0 < YED < 1 → 必需品（缺乏收入弹性）。
Firms use YED to forecast sales growth and shift production as incomes change.
企业利用YED预测销售量增长，并在收入变动时调整生产方向。
3. Cross Elasticity of Demand (XED) | 需求交叉弹性
XED measures the responsiveness of demand for one good to a change in the price of another good. It is the percentage change in quantity demanded of good A divided by the percentage change in price of good B.
需求交叉弹性衡量一种商品的需求对另一种商品价格变动的反应程度，即商品A需求量变动百分比除以商品B价格变动百分比。
XED = %ΔQd(A) ÷ %ΔP(B)
需求交叉弹性 = 商品A需求量变动百分比 ÷ 商品B价格变动百分比
Interpretation: XED > 0 → substitutes; XED < 0 → complements; XED = 0 → unrelated goods. The size reflects closeness of the relationship.
解读：XED > 0 → 替代品；XED < 0 → 互补品；XED = 0 → 无关商品。数值大小反映关系的紧密程度。
4. Price Elasticity of Supply (PES) | 供给价格弹性
PES measures the responsiveness of quantity supplied to a change in price. It is the percentage change in quantity supplied divided by the percentage change in price.
供给价格弹性衡量供给量对价格变动的反应程度，即供给量变动百分比除以价格变动百分比。
PES = %ΔQs ÷ %ΔP
供给价格弹性 = 供给量变动百分比 ÷ 价格变动百分比
PES > 1 → elastic supply; PES < 1 → inelastic supply; PES = 0 → perfectly inelastic; PES = 1 → unit elastic. Key determinants: production time, spare capacity, storage possibilities, complexity of production.
PES > 1 → 供给富有弹性；PES < 1 → 供给缺乏弹性；PES = 0 → 完全无弹性；PES = 1 → 单位弹性。主要决定因素：生产时间、闲置产能、储存可能性、生产复杂程度。
5. Consumer and Producer Surplus | 消费者剩余与生产者剩余
Consumer surplus is the difference between the maximum price consumers are willing to pay and the market price they actually pay. It is represented by the area below the demand curve and above the market price.
消费者剩余是消费者愿意支付的最高价格与实际支付的市场价格之间的差额，在图形上表现为需求曲线下方、市场价格上方的区域。
Producer surplus is the difference between the minimum price producers are willing to accept and the market price they actually receive. It is the area above the supply curve and below the market price.
生产者剩余是生产者愿意接受的最低价格与实际获得的市场价格之间的差额，在图形上为供给曲线上方、市场价格下方的区域。
Total welfare = consumer surplus + producer surplus. Changes in price or government intervention alter the distribution and size of these surpluses.
总福利 = 消费者剩余 + 生产者剩余。价格变动或政府干预会改变剩余的大小与分配。
6. Costs, Revenue and Profit | 成本、收益与利润
Total cost (TC) = Total fixed cost (TFC) + Total variable cost (TVC). Fixed costs do not vary with output; variable costs change as output changes.
总成本(TC) = 总固定成本(TFC) + 总可变成本(TVC)。固定成本不随产量变动，可变成本随产量变化。
AC = TC ÷ Q ; MC = ΔTC ÷ ΔQ
平均成本 = 总成本 ÷ 产量 ; 边际成本 = 总成本变动量 ÷ 产量变动量
Average cost (AC) is total cost per unit; marginal cost (MC) is the additional cost of producing one more unit. Revenue concepts: Total revenue (TR) = Price × Quantity.
平均成本是每单位产量的总成本；边际成本是多生产一单位产品所增加的成本。收益概念：总收益(TR) = 价格 × 数量。
AR = TR ÷ Q ; MR = ΔTR ÷ ΔQ
平均收益 = 总收益 ÷ 产量 ; 边际收益 = 总收益变动量 ÷ 产量变动量
Profit = TR – TC. Normal profit occurs when TR = TC (zero economic profit, covering opportunity cost). Supernormal profit when TR > TC.
利润 = 总收益 – 总成本。正常利润出现在总收益等于总成本时（经济利润为零，涵盖机会成本）。超常利润出现在总收益大于总成本时。
7. Market Structures: Key Conditions | 市场结构：关键条件
Perfect competition: many buyers and sellers, homogeneous products, perfect information, no barriers to entry/exit, firms are price takers. In the long run, only normal profit is earned.
完全竞争：众多买家和卖家、同质产品、完全信息、无进入或退出壁垒、企业是价格接受者。长期中仅能获得正常利润。
Monopoly: single seller, high barriers to entry, price maker. Monopolies can earn supernormal profit in the long run but may be regulated.
垄断：单一卖家、高进入壁垒、价格制定者。垄断企业可在长期获得超常利润，但可能受到监管。
Oligopoly: few dominant firms, interdependent decision-making, product differentiation, barriers to entry. Key models: kinked demand curve, collusion vs competition.
寡头垄断：少数主导企业、决策相互依赖、产品差异化、存在进入壁垒。关键模型：弯折需求曲线，合谋与竞争对比。
Monopolistic competition: many firms, differentiated products, low barriers, some price-setting power, normal profit in the long run.
垄断竞争：众多企业、差异化产品、低进入壁垒、一定的定价能力，长期中趋向正常利润。
Efficiency concepts: allocative efficiency (P = MC), productive efficiency (AC minimum), dynamic efficiency (innovation over time).
效率概念：分配效率（P = MC）、生产效率（最低AC）、动态效率（随时间推移的创新）。
8. Macroeconomic Objectives and Indicators | 宏观经济目标与指标
Main objectives: low and stable inflation, low unemployment, sustained economic growth, balance of payments equilibrium on current account, equitable income distribution.
主要目标：低且稳定的通胀、低失业率、持续经济增长、经常账户平衡、公平的收入分配。
Inflation rate: percentage change in the general price level, commonly measured by CPI (Consumer Price Index). Formula: (Price index current – Price index previous) ÷ Price index previous × 100.
通货膨胀率：一般物价水平的变动百分比，常用CPI（消费价格指数）衡量。公式：(当期价格指数 – 上期价格指数) ÷ 上期价格指数 × 100。
Unemployment rate: (Number of unemployed ÷ labour force) × 100. Claimant count and ILO/LFS measures used in the UK.
失业率：(失业人数 ÷ 劳动力总数) × 100。英国使用申领人数和ILO/LFS衡量标准。
Economic growth: percentage change in real GDP (Gross Domestic Product). Real GDP = Nominal GDP adjusted for inflation.
经济增长：实际GDP（国内生产总值）的变动百分比。实际GDP = 名义GDP扣除通货膨胀影响。
9. Multiplier Effect | 乘数效应
The multiplier shows how an initial injection into the circular flow of income leads to a larger final increase in national income. It arises because one person’s spending becomes another’s income, triggering further rounds of spending.
乘数效应表明，对收入循环流的初始注入会导致国民收入更大幅度的最终增长。其原因是某个人的支出成为另一个人的收入，从而引发新一轮支出。
Multiplier = 1 ÷ (1 – MPC) = 1 ÷ MPS
乘数 = 1 ÷ (1 – 边际消费倾向) = 1 ÷ 边际储蓄倾向
MPC = marginal propensity to consume, MPS = marginal propensity to save, and MPC + MPS = 1. The larger the MPC, the larger the multiplier.
MPC = 边际消费倾向，MPS = 边际储蓄倾向，且MPC + MPS = 1。MPC越大，乘数效应越大。
Other leakages: marginal propensity to tax (MPT) and marginal propensity to import (MPM). With these, multiplier = 1 ÷ (MPS + MPT + MPM).
其他漏出项：边际税收倾向(MPT)和边际进口倾向(MPM)。考虑这些因素后，乘数 = 1 ÷ (MPS + MPT + MPM)。
10. Comparative Advantage and Trade | 比较优势与贸易
A country has a comparative advantage when it can produce a good at a lower opportunity cost than another country. Specialisation and trade according to comparative advantage allow countries to consume beyond their own production possibility frontiers.
若一个国家生产某种商品的机会成本低于另一国，则该国就拥有比较优势。根据比较优势进行专业化生产与贸易，可使各国消费水平超出其生产可能性边界。
Opportunity cost = what is given up / what is gained. For example, if Country A gives up 2 units of cloth to produce 1 unit of wine, its opportunity cost of 1 wine = 2 cloth. Compare with Country B to determine who has the lower opportunity cost.
机会成本 = 放弃的产量 / 获得的产量。例如，若A国为生产1单位葡萄酒而放弃2单位布料，则1酒的机会成本 = 2布。与B国对比，以判断哪国机会成本更低。
The terms of trade must lie between the two countries’ opportunity cost ratios for trade to be mutually beneficial.
贸易条件必须位于两国机会成本比率之间，双方才能从贸易中获益。
11. Equilibrium and Market Mechanism | 均衡与市场机制
Market equilibrium occurs where quantity demanded equals quantity supplied (Qd = Qs). At this point, there is no tendency for price to change. The equilibrium price is also known as the market-clearing price.
市场均衡出现在需求量等于供给量之处（Qd = Qs）。此时价格没有变动趋势，均衡价格也被称为市场出清价格。
If price is above equilibrium, excess supply (surplus) pushes price down. If price is below equilibrium, excess demand (shortage) pushes price up. The price mechanism allocates scarce resources via the signals and incentives provided by prices.
若价格高于均衡水平，超额供给（过剩）将促使价格下跌。若价格低于均衡水平，超额需求（短缺）将推动价格上涨。价格机制通过价格传递的信号和激励来配置稀缺资源。
The functions of price: signalling, rationing, and incentives. Shifts in demand or supply shift the equilibrium point.
价格的功能：信号功能、配给功能和激励功能。需求或供给的移动会使均衡点移动。
12. Government Intervention: Taxes and Subsidies | 政府干预：税收与补贴
Indirect taxes (specific tax or ad valorem tax) increase production costs and shift the supply curve upward/left. The tax burden is shared between consumers and producers depending on PED and PES.
间接税（从量税或从价税）增加生产成本，使供给曲线向上/左移动。税负在消费者和生产者之间的分配取决于需求价格弹性和供给价格弹性。
Consumer burden = (Pc – Pe) × Q after tax; Producer burden = (Pe – Pp) × Q after tax. The more inelastic the demand or supply, the greater the burden on that side.
消费者负担 = （消费者支付价格 – 原均衡价格） × 税后数量；生产者负担 = （原均衡价格 – 生产者净得价格） × 税后数量。需求或供给越缺乏弹性，该方承担的税负越重。
Subsidies lower production costs and shift supply downward/right. They increase quantity consumed and reduce market price, but have an opportunity cost for the government.
补贴降低生产成本，使供给曲线向下/右移动。补贴增加消费量并降低市场价格，但对政府而言存在机会成本。
Welfare effects: taxes create deadweight loss; subsidies also may create deadweight loss if not targeted correctly.
福利影响：税收造成无谓损失；若补贴未精准投放，也可能导致无谓损失。
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