📚 A-Level Economics: Formula Handbook | A-Level 经济：公式汇总手册
Mastering the essential formulas is a crucial step towards achieving top grades in A-Level Economics. Whether you are tackling microeconomic calculations or macroeconomic indicators, a firm grasp of these equations will help you analyse real-world data, evaluate policies and write precise examination answers. This handbook brings together the most important formulas grouped by topic, with clear explanations in both English and Chinese, so you can revise efficiently and confidently.
掌握核心公式是迈向 A-Level 经济高分的关键一步。不论你面对的是微观经济计算还是宏观经济指标，牢固掌握这些等式将帮助你分析现实数据、评估政策并写出精准的考试答案。本手册按主题汇总了最重要的公式，并配有清晰的中英文解释，让你可以高效而自信地复习。
1. Price Elasticity of Demand (PED) | 需求价格弹性
Price elasticity of demand measures the responsiveness of quantity demanded to a change in the good’s own price. It is calculated by dividing the percentage change in quantity demanded by the percentage change in price.
需求价格弹性衡量需求量对商品自身价格变化的反应程度。它的计算方法是用需求量的百分比变化除以价格的百分比变化。
PED = %Δ Quantity Demanded / %Δ Price
If PED > 1, demand is price elastic; if PED < 1, demand is price inelastic; and if PED = 1, demand is unit elastic. The sign is typically negative due to the law of demand, but economists often ignore the minus sign and work with absolute values.
如果 PED > 1，需求是富有价格弹性的；如果 PED < 1，需求是缺乏价格弹性的；如果 PED = 1，需求是单位弹性。由于需求定律，该值通常为负，但经济学家通常忽略负号，使用绝对值。
Point elasticity uses the derivative approach: PED = (dQ/dP) × (P/Q). The midpoint (arc) formula is often preferred when dealing with discrete data to avoid inconsistency: PED = [(Q₂ – Q₁)/((Q₁+Q₂)/2)] ÷ [(P₂ – P₁)/((P₁+P₂)/2)].
点弹性使用导数方法：PED = (dQ/dP) × (P/Q)。在处理离散数据时，通常更倾向于使用中点（弧）公式，以避免不一致：PED = [(Q₂ – Q₁)/((Q₁+Q₂)/2)] ÷ [(P₂ – P₁)/((P₁+P₂)/2)]。
2. Price Elasticity of Supply (PES) | 供给价格弹性
Price elasticity of supply captures the degree to which quantity supplied responds to changes in price. The formula mirrors that of PED but uses quantity supplied instead of quantity demanded.
供给价格弹性衡量供给量对价格变化的反应程度。公式与 PED 类似，只是用供给量替代了需求量。
PES = %Δ Quantity Supplied / %Δ Price
A value greater than 1 indicates elastic supply (producers can easily adjust output), while a value less than 1 indicates inelastic supply (output is difficult to change in the short run). The PES is always positive because the supply curve slopes upward.
数值大于 1 表示富有供给弹性（生产者可以轻松调整产量），小于 1 表示缺乏供给弹性（短期内产量难以改变）。由于供给曲线向上倾斜，PES 始终为正。
The determining factors include time period, availability of spare capacity, and the ease of shifting resources. In the long run, supply tends to be more elastic.
决定因素包括时间周期、闲置产能的可得性以及资源转移的难易程度。长期中，供给通常更富有弹性。
3. Income Elasticity of Demand (YED) | 需求收入弹性
Income elasticity of demand measures how sensitive the demand for a good is to changes in consumers’ income. It is vital for classifying goods and forecasting shifts in demand as economies grow.
需求收入弹性衡量一种商品的需求对消费者收入变化的敏感程度。它对商品分类以及预测经济增长时需求的变化至关重要。
YED = %Δ Quantity Demanded / %Δ Income
For normal goods, YED is positive: necessities have a YED between 0 and 1, while luxury goods have a YED greater than 1. For inferior goods, YED is negative, meaning demand falls as income rises.
正常品的 YED 为正：必需品的 YED 在 0 到 1 之间，奢侈品的 YED 大于 1。低档品的 YED 为负，意味着收入增加时需求下降。
Firms use YED estimates to plan production and investment decisions. During a recession, producers of inferior goods may see sales increase, while luxury car manufacturers face a sharp contraction.
企业运用 YED 估算来规划生产和投资决策。经济衰退时，低档品生产商的销量可能上升，而豪华汽车制造商则面临急剧萎缩。
4. Cross Elasticity of Demand (XED) | 需求交叉弹性
Cross elasticity of demand reveals the relationship between two different goods. It is the percentage change in the quantity demanded of good A divided by the percentage change in the price of good B.
需求交叉弹性揭示两种不同商品之间的关系。它是商品 A 需求量的百分比变化除以商品 B 价格的百分比变化。
XED = %Δ Quantity Demanded of Good A / %Δ Price of Good B
A positive XED indicates that the two goods are substitutes (e.g., tea and coffee). A negative XED indicates that they are complements (e.g., smartphones and apps). A value close to zero suggests that the goods are unrelated.
XED 为正表示两种商品是替代品（如茶与咖啡）。XED 为负表示它们是互补品（如智能手机与应用程序）。数值接近于零则表示两者不相关。
Businesses use XED to anticipate the impact of competitors’ pricing strategies and to design effective marketing campaigns. This measure also helps government assess mergers and market definitions.
企业利用 XED 来预测竞争对手定价策略的影响，并设计有效的营销活动。这一指标也有助于政府评估并购和界定市场。
5. Total Revenue, Average Revenue and Marginal Revenue | 总收益、平均收益与边际收益
Revenue concepts lie at the heart of firms’ pricing and output decisions. Total revenue (TR) is the income a firm receives from selling its output; average revenue (AR) is revenue per unit sold, which equals price; marginal revenue (MR) is the addition to total revenue from selling one more unit.
收益概念是企业定价和产量决策的核心。总收益（TR）是企业销售产品所获得的收入；平均收益（AR）是每单位销售的收入，通常等于价格；边际收益（MR）是每多销售一单位产品所带来的总收益增加量。
TR = Price × Quantity
AR = TR / Q = Price
MR = ΔTR / ΔQ
In perfectly competitive markets, MR equals AR and both are constant. In imperfect competition, a firm must lower price to sell more, so MR lies below AR and can become negative if output expands too far.
在完全竞争市场中，MR 等于 AR 且两者均为常数。在不完全竞争市场中，企业必须降价才能卖出更多，因此 MR 低于 AR，并且如果产量扩大过多，MR 可能变为负。
Profit maximisation occurs where marginal cost equals marginal revenue (MC = MR). This rule applies regardless of market structure.
利润最大化发生在边际成本等于边际收益（MC = MR）之处。这一规则适用于任何市场结构。
6. Costs, Profit and Efficiency | 成本、利润与效率
Understanding cost structures is essential for analysing firm behaviour. Key concepts include total cost (TC), fixed cost (FC), variable cost (VC), average total cost (ATC), and marginal cost (MC).
理解成本结构对分析企业行为至关重要。关键概念包括总成本（TC）、固定成本（FC）、可变成本（VC）、平均总成本（ATC）和边际成本（MC）。
TC = FC + VC
ATC = TC / Q
AVC = VC / Q
AFC = FC / Q
MC = ΔTC / ΔQ
Profit is the difference between total revenue and total cost. Accounting profit considers only explicit costs, while economic profit subtracts both explicit and implicit (opportunity) costs. Normal profit occurs when total revenue equals total cost, meaning the firm is covering all its opportunity costs.
利润是总收益与总成本之间的差额。会计利润只考虑显性成本，而经济利润既扣除显性成本也扣除隐性（机会）成本。正常利润发生在总收益等于总成本时，意味着企业刚好弥补了所有机会成本。
Profit = TR – TC
Normal Profit: TR = TC (so Economic Profit = 0)
Productive efficiency is achieved when output is produced at the lowest possible average cost (the minimum point of the ATC curve). Allocative efficiency occurs where price equals marginal cost (P = MC), meaning resources reflect consumer preferences.
当以最低的可能平均成本（ATC 曲线的最低点）生产时，实现了生产效率。配置效率发生在价格等于边际成本（P = MC）时，意味着资源配置反映了消费者偏好。
7. National Income Multiplier | 国民收入乘数
The multiplier effect explains how an initial injection into the circular flow of income can lead to a larger final increase in national income. It depends on the marginal propensity to consume (MPC), the marginal propensity to save (MPS), the marginal propensity to tax (MPT), and the marginal propensity to import (MPM).
乘数效应解释了初始注入经济循环流会如何导致国民收入产生更大的最终增加。它取决于边际消费倾向（MPC）、边际储蓄倾向（MPS）、边际税收倾向（MPT）和边际进口倾向（MPM）。
Multiplier (k) = 1 / (1 – MPC)
or k = 1 / (MPS + MPT + MPM)
The simple closed-economy multiplier with no government or foreign trade is 1/MPS. In an open economy with government, the denominator expands to include withdrawals: 1 / (MPS + MPT + MPM). The larger the withdrawals, the smaller the multiplier.
没有政府与对外贸易的简单封闭经济乘数是 1/MPS。在有政府的开放经济中，分母会扩展以涵盖所有漏出：1 / (MPS + MPT + MPM)。漏出越大，乘数越小。
Changes in aggregate demand can be calculated using: Δ National Income = k × Δ Injection. This tool helps assess the effectiveness of fiscal policy.
总需求的变化可以通过下式计算：国民收入变化量 = k × 注入变化量。此工具有助于评估财政政策的有效性。
8. Aggregate Demand and GDP Calculations | 总需求与 GDP 计算
Gross domestic product (GDP) can be calculated through three equivalent approaches: expenditure, income, and output. The expenditure method is common in A-Level analysis and forms the basis of the aggregate demand formula.
国内生产总值（GDP）可以通过三种等效方法计算：支出法、收入法和产出法。支出法在 A-Level 分析中常见，并构成总需求公式的基础。
Aggregate Demand (AD) = Consumption (C) + Investment (I) + Government Spending (G) + (Exports (X) – Imports (M))
GDP at market prices includes indirect taxes and subtracts subsidies. GDP at factor cost, used in the income method, adds back subsidies and removes indirect taxes. GDP per capita is obtained by dividing GDP by the population.
按市场价格计算的 GDP 包含间接税并减去补贴。用于收入法的要素成本 GDP 则加回补贴并扣除间接税。人均 GDP 由 GDP 除以人口得出。
GDP at Market Prices = C + I + G + (X – M)
GDP at Factor Cost = GDP at Market Prices – Indirect Taxes + Subsidies
GDP per Capita = GDP / Population
Real GDP is nominal GDP adjusted for inflation, using a price deflator. This gives a more accurate picture of economic growth.
实际 GDP 是名义 GDP 根据通货膨胀调整后的结果，使用价格平减指数。这可以更准确地反映经济增长。
9. Inflation and Index Numbers | 通货膨胀与指数
Inflation measures the sustained increase in the general price level. The most common calculations involve the Consumer Price Index (CPI) and the Retail Price Index (RPI), as well as the GDP deflator.
通货膨胀衡量一般价格水平的持续上升。最常见的计算涉及消费者价格指数（CPI）、零售价格指数（RPI）以及 GDP 平减指数。
Inflation Rate (%) = [(Index in Current Year – Index in Previous Year) / Index in Previous Year] × 100
Constructing a price index involves selecting a base year, assigning weights to a basket of goods, and tracking price changes. The index in the base year is usually set to 100.
构建价格指数涉及选择基年、为一篮子商品分配权重并追踪价格变化。基年的指数通常设为 100。
Index = (Total Cost of Basket in Current Year / Total Cost of Basket in Base Year) × 100
Real values are derived by dividing nominal values by the price index (multiplied by 100). This allows economists to distinguish between nominal changes and genuine increases in purchasing power.
实际值通过名义值除以价格指数（再乘以 100）得出。这使经济学家能够区分名义变化与购买力的真正增长。
10. Unemployment Rate | 失业率
The unemployment rate is a key macroeconomic performance indicator. It is defined as the percentage of the labour force that is actively seeking work but unable to find employment.
失业率是一个关键的宏观经济表现指标。它被定义为劳动力中积极寻找工作但无法就业的人数所占的百分比。
Unemployment Rate (%) = (Number of Unemployed Workers / Labour Force) × 100
The labour force includes both the employed and the unemployed, excluding those who are economically inactive (students, retirees, discouraged workers). Therefore, the participation rate also matters: Participation Rate = (Labour Force / Working-Age Population) × 100.
劳动力包括就业者和失业者，不包括非经济活动人口（学生、退休人员、失去信心的劳动者）。因此，参与率也很重要：参与率 = （劳动力 / 劳动年龄人口）× 100。
Policies to reduce unemployment depend on the type: cyclical (demand-deficient), structural, frictional, or seasonal. Understanding the formula helps evaluate whether a falling unemployment rate truly indicates a healthier labour market.
降低失业的政策取决于失业类型：周期性（需求不足）、结构性、摩擦性或季节性。理解该公式有助于判断下降的失业率是否真意味着劳动力市场更加健康。
11. Balance of Payments and Exchange Rates | 国际收支与汇率
The current account of the balance of payments records trade in goods, trade in services, primary income (investment income and wages) and secondary income (transfers). A country’s trade balance is simply the difference between exports and imports of goods and services.
国际收支中的经常账户记录货物贸易、服务贸易、初次收入（投资收入和工资）和二次收入（转移）。一国的贸易平衡就是商品和服务出口与进口的差额。
Current Account Balance = (Exports of Goods + Services) – (Imports of Goods + Services) + Net Primary Income + Net Secondary Income
Exchange rates can be expressed as the price of one currency in terms of another. When using weighted indices, the exchange rate index shows the value of a currency against a basket of other currencies.
汇率可以表示为一单位货币以另一种货币计价的价格。使用加权指数时，汇率指数显示一种货币相对于一篮子其他货币的价值。
Exchange Rate Index = Σ (Weight × (Exchange Rate in Current Period / Exchange Rate in Base Period) × 100)
Depreciation of the domestic currency makes exports cheaper and imports dearer, potentially improving the trade balance, provided the Marshall-Lerner condition holds: the sum of price elasticities of demand for exports and imports must be greater than 1 in absolute terms.
本币贬值会使出口更便宜、进口更昂贵，从而可能改善贸易平衡，前提是马歇尔-勒纳条件成立：出口和进口的需求价格弹性绝对值之和必须大于 1。
12. Money Multiplier and Credit Creation | 货币乘数与信用创造
In the money creation process, commercial banks can lend out a multiple of the reserves they hold. The simple money multiplier links the monetary base to the broader money supply, assuming banks do not hold excess reserves and the public does not hold additional cash.
在货币创造过程中，商业银行可以贷出其持有准备金的多倍。简单的货币乘数将基础货币与更广义的货币供给联系起来，假设银行不持有超额准备金且公众不额外持有现金。
Money Multiplier = 1 / Reserve Requirement Ratio
For example, if the reserve ratio is 0.1 (10%), the multiplier is 10, meaning an initial deposit of £1,000 can potentially generate up to £10,000 in new money. In practice, leakages (extra cash holdings, cautious lending) reduce the actual multiplier.
例如，如果准备金率是 0.1（10%），乘数为 10，意味着 1,000 英镑的初始存款最终可以创造多达 10,000 英镑的新货币。在现实中，漏出（额外持有现金、谨慎放贷）会降低实际乘数。
Central banks use the reserve requirement as a tool of monetary policy, though it is less commonly adjusted than interest rates in advanced economies in recent years.
央行将准备金率作为货币政策工具之一，尽管近年来在发达经济体中其使用频率低于利率调整。
Published by TutorHao | Economics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导