📚 IB & WJEC Economics Formula Handbook | IB与WJEC经济公式汇总手册
This handbook brings together every essential formula you need for IB and WJEC Economics – from microelasticities and cost structures to macroeconomic multipliers, inflation measures and trade indicators. Clear definitions, worked-style notation and bilingual explanations help you revise efficiently and apply the right formula under exam pressure.
本手册汇集了 IB 和 WJEC 经济学所需的所有核心公式——从微观弹性、成本结构到宏观经济乘数、通货膨胀指标和贸易指数。清晰的公式表达、中英双语的要点讲解，帮助你高效复习，在考试压力下准确调用公式。
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 as the percentage change in quantity demanded divided by the percentage change in price, and the result is usually expressed as an absolute value.
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。计算公式为需求量变动的百分比除以价格变动的百分比，结果通常取绝对值。
PED = %ΔQd ÷ %ΔP
If |PED| > 1, demand is price elastic — a price fall raises total revenue. If |PED| < 1, demand is price inelastic — a price rise raises total revenue. Unit elasticity occurs when |PED| = 1 and total revenue remains constant as price changes.
若 |PED| > 1，需求富有弹性——降价会增加总收益。若 |PED| < 1，需求缺乏弹性——提价会增加总收益。当 |PED| = 1 时为单位弹性，价格变动不会改变总收益。
A straight‑line demand curve has varying elasticity: elastic above the midpoint, unit elastic at the midpoint and inelastic below it. The slope of the demand curve alone does not determine elasticity; percentage changes matter.
直线型需求曲线上各点的弹性是变化的：中点以上富有弹性，中点处为单位弹性，中点以下缺乏弹性。仅凭需求曲线的斜率不能确定弹性，关键在于百分比的变动。
2. Income Elasticity of Demand (YED) & Cross Elasticity of Demand (XED) | 收入弹性与交叉弹性
Income elasticity of demand (YED) shows how quantity demanded changes in response to a change in consumer income. It helps classify goods as normal (YED > 0) or inferior (YED < 0). Luxury goods have YED > 1, while necessities have 0 < YED < 1.
收入弹性（YED）反映需求量对消费者收入变化的反应程度。它有助于将商品分为正常品（YED > 0）或低档品（YED < 0）。奢侈品 YED > 1，必需品 0 < YED < 1。
YED = %ΔQd ÷ %ΔIncome
Cross elasticity of demand (XED) measures how the quantity demanded of one good reacts to a price change of another good. Positive XED indicates substitutes, negative XED indicates complements, and near‑zero XED suggests unrelated goods.
交叉弹性（XED）衡量一种商品的需求量对另一种商品价格变动的反应程度。XED 为正，表明二者互为替代品；为负则是互补品；接近于零则表示不相关商品。
XED = %ΔQd of Good X ÷ %ΔP of Good Y
3. Price Elasticity of Supply (PES) | 供给价格弹性
Price elasticity of supply captures the responsiveness of quantity supplied to a change in the good’s price. It is always positive in standard supply curves because of the law of supply.
供给价格弹性反映供给量对商品自身价格变动的反应程度。由于供给定律，标准供给曲线上的 PES 恒为正值。
PES = %ΔQs ÷ %ΔP
Supply is elastic when PES > 1, inelastic when PES < 1, and unit elastic when PES = 1. The time period is a key determinant: supply is usually more elastic in the long run as firms can adjust all inputs.
当 PES > 1 时，供给富有弹性；PES < 1 为缺乏弹性；PES = 1 为单位弹性。时间长短是关键决定因素——长期中企业可调整全部要素投入，供给通常更具弹性。
Perfectly inelastic supply (PES = 0) is vertical, while perfectly elastic supply (PES = ∞) is horizontal. These extremes often appear in fixed‑quantity goods or in perfectly competitive markets.
完全无弹性供给（PES = 0）是一条垂直线，完全有弹性供给（PES = ∞）是一条水平线。这两种极端情况常见于数量固定的商品或完全竞争市场。
4. Consumer Surplus & Producer Surplus | 消费者剩余与生产者剩余
Consumer surplus is the difference between what consumers are willing to pay and what they actually pay. On a diagram it is 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价格之间的差额。在图形中，它表现为需求曲线以下、市场价格以上的区域。
Consumer Surplus = ½ × (Maximum willingness to pay − Market price) × Quantity
Producer surplus is the difference between the market price received and the minimum price at which producers are willing to supply. It is the area above the supply curve and below the market price.
生产者剩余是生产者实际收到的市场价格与其愿意接受的最低价格之间的差额。它是供给曲线以上、市场价格以下的区域。
Producer Surplus = ½ × (Market price − Minimum supply price) × Quantity
Total welfare in a market is the sum of consumer and producer surplus. Government interventions such as taxes or price controls can shrink these surpluses and create deadweight loss.
市场总福利是消费者剩余与生产者剩余之和。征税或价格管制等政府干预会减少这些剩余并产生无谓损失。
5. Costs of Production: TC, AC, MC | 生产成本：总成本、平均成本与边际成本
Total cost (TC) comprises total fixed cost (TFC) and total variable cost (TVC). Fixed costs do not change with output, while variable costs vary directly with output in the short run.
总成本（TC）由总固定成本（TFC）和总可变成本（TVC）组成。固定成本不随产量变化，而可变成本在短期中随产量直接变动。
TC = TFC + TVC
Average total cost (ATC or AC) is total cost divided by the quantity of output. It can also be expressed as the sum of average fixed cost (AFC) and average variable cost (AVC).
平均总成本（ATC 或 AC）等于总成本除以产出数量，也可以表示为平均固定成本（AFC）与平均可变成本（AVC）之和。
ATC = TC ÷ Q | AFC = TFC ÷ Q | AVC = TVC ÷ Q
Marginal cost (MC) is the addition to total cost from producing one more unit of output. MC typically falls briefly then rises due to the law of diminishing marginal returns.
边际成本（MC）是多生产一单位产品所带来的总成本增加量。由于边际报酬递减规律，MC 通常短暂下降后转为上升。
MC = ΔTC ÷ ΔQ
6. Revenue and Profit: TR, AR, MR | 收益与利润：总收益、平均收益与边际收益
Total revenue (TR) is the income a firm receives from selling its output. It equals price multiplied by quantity sold. Average revenue (AR) equals total revenue divided by quantity, which is identical to the price when all units are sold at the same price.
总收益（TR）是企业销售产品所得的收入，等于价格乘以销售量。平均收益（AR）等于总收益除以数量，在统一定价下与价格相等。
TR = P × Q | AR = TR ÷ Q = P
Marginal revenue (MR) is the change in total revenue from selling one additional unit. Under perfect competition MR = AR = P. In imperfect competition, MR lies below AR and the firm must lower price to sell more.
边际收益（MR）是多销售一单位产品所带来的总收益增量。在完全竞争下 MR = AR = P。在不完全竞争下，MR 低于 AR，因为企业必须降价才能增加销量。
MR = ΔTR ÷ ΔQ
Profit (π) equals total revenue minus total cost. A normal profit is earned when TR = TC (zero economic profit). Abnormal (supernormal) profit occurs when TR > TC.
利润（π）等于总收益减去总成本。当 TR = TC 时获得正常利润（经济利润为零）；当 TR > TC 时获得超额（超常）利润。
Profit = TR − TC
7. Profit Maximisation and Shut‑down Point | 利润最大化与停止营业点
A firm maximises profit where marginal cost equals marginal revenue, provided MC cuts MR from below. This is the profit‑maximising rule for all market structures.
当边际成本等于边际收益，且 MC 从下方穿过 MR 时，企业实现利润最大化。这是所有市场结构通用的利润最大化法则。
Profit‑maximising output: MC = MR
If a firm is making a loss in the short run, it should continue operating if price covers average variable cost (P ≥ AVC). If price falls below AVC, the firm minimises loss by shutting down.
若企业在短期中面临亏损，只要价格能弥补平均可变成本（P ≥ AVC），就应继续经营。一旦价格低于 AVC，企业应停止生产以最小化亏损。
Shut‑down condition: P < AVC
The break‑even point occurs where price equals average total cost (P = ATC), yielding normal profit. This marks the entry and exit threshold in the long run.
盈亏平衡点出现在价格等于平均总成本（P = ATC）时，此时企业获利正常利润。这也是长期中厂商进入或退出市场的门槛。
8. Aggregate Demand and the Multiplier | 总需求与乘数
The marginal propensity to consume (MPC) is the fraction of additional income that households spend on consumption. The marginal propensity to save (MPS) is the fraction saved. Together they sum to one.
边际消费倾向（MPC）是家庭将新增收入用于消费的比例。边际储蓄倾向（MPS）是用于储蓄的比例。两者之和为 1。
MPC + MPS = 1 | MPC = ΔC ÷ ΔY | MPS = ΔS ÷ ΔY
The simple spending multiplier (k) shows how much real GDP changes in response to an initial change in autonomous spending. A larger MPC means a larger multiplier.
简单支出乘数（k）反映了实际 GDP 对自主支出初始变动的放大倍数。MPC 越大，乘数效应越强。
Multiplier k = 1 ÷ (1 − MPC) = 1 ÷ MPS
The change in national income is the product of the multiplier and the initial injection: ΔY = k × ΔJ. In an open economy, the multiplier is smaller because of leakages such as imports and taxes.
国民收入的变动量等于乘数乘以初始注入：ΔY = k × ΔJ。在开放经济中，由于进口和税收等漏出项，乘数会变小。
9. Inflation and Price Indices | 通货膨胀与价格指数
A consumer price index (CPI) measures the average change in prices of a fixed basket of goods and services. It is the most common gauge of the cost of living.
消费者价格指数（CPI）衡量一篮子固定商品和服务的平均价格变动，是最常用的生活成本度量指标。
CPI = (Cost of basket in current year ÷ Cost of basket in base year) × 100
The inflation rate is the year‑on‑year percentage change in the price index. It shows how quickly the general price level is rising.
通货膨胀率是价格指数的同比百分比变动，反映一般物价水平的上涨速度。
Inflation Rate = [(CPI₂ − CPI₁) ÷ CPI₁] × 100
The GDP deflator captures price changes for all domestically produced goods and services, not just consumer items. It equals nominal GDP divided by real GDP times 100.
GDP 平减指数涵盖国内生产的所有商品和服务的价格变化，而不仅是消费品。它等于名义 GDP 除以实际 GDP 再乘以 100。
GDP Deflator = (Nominal GDP ÷ Real GDP) × 100
10. Unemployment and Labour Market Indicators | 失业与劳动力市场指标
The unemployment rate expresses the number of people actively seeking work but unable to find it as a percentage of the labour force. The labour force includes both employed and unemployed individuals.
失业率反映积极寻找工作但未能找到的人数占劳动力人口的百分比。劳动力人口包括就业者和失业者。
Unemployment Rate = (Number of Unemployed ÷ Labour Force) × 100
The labour force participation rate shows what share of the working‑age population is either employed or actively looking for work. It indicates how engaged an economy’s potential workers are in the labour market.
劳动参与率表示适龄劳动人口中就业或正在积极求职的比例，揭示一个经济体的潜在劳动力参与市场的程度。
Participation Rate = (Labour Force ÷ Working‑age Population) × 100
Employment rate, by contrast, measures the percentage of the working‑age population that is in employment. It complements the unemployment figure when assessing labour market health.
相比之下，就业率衡量的是适龄劳动人口中已就业的比例，与失业率一同使用时可以更全面地评估劳动力市场状况。
11. International Trade: Comparative Advantage and Terms of Trade | 国际贸易：比较优势与贸易条件
Comparative advantage exists when a country can produce a good at a lower opportunity cost than another country. Opportunity cost is the quantity of one good given up to produce one additional unit of the other.
当一国能以低于另一国的机会成本生产某种商品时，该国就具有比较优势。机会成本是为了多生产一单位某商品而放弃的另一种商品的数量。
Opportunity Cost of Good X = ΔGood Y ÷ ΔGood X
Terms of trade measures the ratio of export prices to import prices. An improvement means a country can buy more imports with a given quantity of exports.
贸易条件衡量出口价格与进口价格之比。贸易条件改善意味着同样数量的出口可以换回更多的进口商品。
Terms of Trade = (Index of Export Prices ÷ Index of Import Prices) × 100
Countries specialise based on comparative advantage and trade for mutual gain, provided the terms of trade lie between the two nations’ domestic opportunity cost ratios.
各国基于比较优势进行专业化并开展贸易，双方均可获益，前提是贸易条件落在两国国内机会成本比率之间。
12. Exchange Rates and Balance of Payments | 汇率与国际收支
An exchange rate expresses the price of one currency in terms of another. In a floating system the rate is determined by supply and demand for currencies; in a fixed system it is pegged by the central bank.
汇率以一种货币表示另一种货币的价格。在浮动汇率制下，汇率由外汇供求决定；在固定汇率制下，汇率由中央银行钉住。
The current account balance summarises trade in goods, services, primary income and secondary income. A deficit occurs when debits exceed credits; a surplus is the opposite.
经常账户余额概括了货物、服务、初次收入和二次收入的交易。支出大于收入时出现赤字，反之则为盈余。
Current Account Balance = (X − M) + Net Income + Net Transfers
When a country runs a current account deficit, it must be financed by a surplus on the financial and capital accounts, or by running down official reserves. Over time, persistent deficits may put downward pressure on a floating currency.
当一国出现经常账户赤字时，必须通过金融和资本账户的顺差或动用官方储备来融资。长期持续的赤字可能会对浮动货币产生贬值压力。
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