📚 Year 13 Edexcel Economics: Formula & Theorem Quick Reference Handbook | A-Level Edexcel 经济：公式定理速查手册
This quick reference handbook compiles every essential formula, equation and key economic relationship that appears in the Year 13 Edexcel Economics A specification. From microeconomic elasticities and cost structures to macroeconomic multipliers and international trade measures, the content is presented with clear explanations and, where helpful, worked examples. Use it to sharpen your final revision and build confidence for the exams.
本速查手册汇集了 Year 13 Edexcel Economics A 课程中涉及的所有关键公式、方程和重要经济关系。从微观弹性与成本结构到宏观乘数与国际贸易指标，每一项都配有清晰的解释并在适当处附上示例。用它来强化冲刺复习，为考试增强信心。
1. Price, Income and Cross Elasticities | 价格弹性、收入弹性与交叉弹性
Elasticities measure the responsiveness of one variable to a change in another. They are among the most frequently tested quantitative skills in Edexcel Economics.
弹性衡量一个变量对另一变量变动的反应程度，是 Edexcel 经济学中最常考查的定量技能之一。
Price elasticity of demand (PED) quantifies how quantity demanded reacts to a price change.
需求价格弹性（PED）量化需求量对价格变化的反应。
PED = %ΔQd / %ΔP
其中 %ΔQd 表示需求量的百分比变化，%ΔP 表示价格的百分比变化。计算时始终取绝对值；若 |PED| > 1 则需求富有弹性，若 |PED| < 1 则缺乏弹性，单位弹性时等于 1。
Income elasticity of demand (YED) captures the change in demand as consumer income changes.
需求收入弹性（YED）反映消费者收入变化时需求的变化。
YED = %ΔQd / %ΔY
Y 代表收入。正常商品的 YED 为正（奢侈品 YED > 1，必需品 0 < YED < 1），低档商品的 YED 为负。
Cross elasticity of demand (XED) measures how the demand for one good responds to a price change of another good.
需求交叉弹性（XED）衡量一种商品的需求对另一种商品价格变化的反应。
XED = %ΔQd of good A / %ΔP of good B
若 XED 为正，则两种商品互为替代品；若为负，则为互补品；接近零则表示二者为独立品。
Price elasticity of supply (PES) shows the responsiveness of quantity supplied to a price change.
供给价格弹性（PES）表示供给量对价格变化的反应程度。
PES = %ΔQs / %ΔP
PES 恒为正值。值大于 1 表示供给富有弹性，小于 1 表示缺乏弹性，等于 1 为单位弹性。
2. Costs, Revenues and Profit | 成本、收益与利润
Understanding cost and revenue structures is fundamental for analysing firm behaviour. The relationships below underpin profit calculations in every market structure.
理解成本与收益结构是分析企业行为的基础。以下关系是各种市场结构中利润计算的基石。
Total cost (TC) is the sum of all fixed and variable costs.
总成本（TC）是所有固定成本与可变成本之和。
TC = Total Fixed Cost (TFC) + Total Variable Cost (TVC)
平均成本（AC = TC / 产量 Q）和边际成本（MC = ΔTC / ΔQ）决定了企业的供给决策。当 MC < AC 时，AC 下降；MC > AC 时，AC 上升；MC 与 AC 的交点就是 AC 的最低点。
Total revenue (TR) is the income from selling output, while average revenue (AR) is the price.
总收益（TR）是销售产出获得的收入，平均收益（AR）等于价格。
TR = Price (P) × Quantity (Q) | AR = TR / Q = P
Marginal revenue (MR) is the addition to total revenue from selling one more unit.
边际收益（MR）是增加销售一单位产品所带来的总收益增量。
MR = ΔTR / ΔQ
在完全竞争市场中，MR 恒等于价格；在不完全竞争市场中，MR 曲线低于需求（AR）曲线。
Profit is the difference between total revenue and total cost.
利润是总收益与总成本之差。
Profit = TR – TC
正常利润隐含在 TC 中（即零经济利润），超常利润指 TR > TC（包括隐性成本部分）。
3. Profit Maximisation and Efficiency Conditions | 利润最大化与效率条件
Firms are assumed to aim for profit maximisation, and policymakers care about efficiency. These conditions are repeated throughout the Theme 3 and Theme 4 content.
企业根本目标是利润最大化，而政策制定者关注效率。这些条件在 Theme 3 和 Theme 4 中反复出现。
The profit-maximising rule is marginal revenue equals marginal cost.
利润最大化规则是边际收益等于边际成本。
MR = MC
只要 MR > MC，增产就可增加利润；当 MR < MC 时，企业应减产。利润最大化产量出现在 MR 与 MC 的交点。
Allocative efficiency occurs where price equals marginal cost.
分配效率出现在价格等于边际成本时。
P = MC
该条件意味着资源被配置于消费者最看重的用途，社会总剩余最大化。
Productive efficiency requires output at the minimum average total cost.
生产效率要求在平均总成本最低点生产。
ATC is at its minimum
此时企业以最小的单位成本生产，避免了浪费。
Dynamic efficiency focuses on innovation and cost reduction over time, often associated with supernormal profits reinvested in R&D.
动态效率关注长期中的创新与成本下降，常与再投入研发带来的超常利润相关。
4. Market Concentration Measures | 市场集中度衡量
Competition authorities use concentration ratios and the Herfindahl-Hirschman Index (HHI) to assess market power. Both appear in Edexcel exam questions.
竞争监管机构用集中度比率和赫芬达尔-赫希曼指数（HHI）评估市场势力，两者均常见于 Edexcel 考题。
An n-firm concentration ratio sums the market shares of the largest n firms.
n 企业集中度比率是前 n 大企业市场份额之和。
CRn = (Sum of market shares of top n firms) × 100
例如 CR5 = 80% 表示前五大企业占据 80% 的市场，通常高度集中。
The Herfindahl-Hirschman Index squares each firm’s market share and sums them.
赫芬达尔-赫希曼指数将每家企业的市场份额平方后求和。
HHI = Σ (market share of each firm)²
HHI 的值介于 0（完全竞争）和 10000（纯垄断）之间。Edexcel 通常采用小数或百分比平方，总分 0 到 1 或 0 到 10000；计算时务必遵循题目要求。
5. Labour Market and Marginal Revenue Product | 劳动市场与边际收益产品
The demand for labour is derived from the demand for goods and services. The key concept is marginal revenue product (MRP).
劳动需求源于对商品和服务的需求，核心概念是边际收益产品（MRP）。
MRP measures the additional revenue gained from employing one more unit of labour.
MRP 衡量多雇佣一单位劳动所增加的收入。
MRP = Marginal Physical Product (MPP) × Marginal Revenue (MR)
如果在完全竞争的产品市场，MR = P，因此 MRP = MPP × P，此时常被称为边际产值（VMP）。但若产品市场不完全，MR 随产量下降，MRP 也下降得更快。
A profit-maximising firm hires labour up to the point where MRP equals the marginal cost of labour.
追求利润最大化的企业会一直雇佣劳动，直到 MRP 等于劳动的边际成本。
MRP = Marginal Cost of Labour (wage rate in perfect markets)
在完全竞争的劳动力市场，边际劳动成本等于工资率；在买方垄断的市场，MCL 高于工资率，导致雇佣量减少。
6. National Income Multiplier | 国民收入乘数
The multiplier explains how an initial injection of spending leads to a larger final increase in national income. It is central to fiscal policy analysis.
乘数解释一次初始支出注入如何最终带来国民收入的更大增长，是财政政策分析的核心。
The simple multiplier depends on the marginal propensity to consume (MPC).
简单乘数取决于边际消费倾向（MPC）。
k = 1 / (1 – MPC) = 1 / MPS
其中 MPS 为边际储蓄倾向，MPS = 1 – MPC。
With government and foreign trade, the multiplier becomes smaller due to leakages.
考虑政府与对外贸易后，漏出使乘数变小。
k = 1 / (MPS + MPT + MPM)
MPT 为边际税率倾向（即收入增量中用于缴税的比例），MPM 为边际进口倾向。该乘数
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