IGCSE OCR Economics: Formula Summary Handbook | IGCSE OCR 经济：公式汇总手册

📚 IGCSE OCR Economics: Formula Summary Handbook | IGCSE OCR 经济：公式汇总手册

Mastering the key formulas is essential for success in IGCSE OCR Economics. This handbook compiles all the quantitative relationships and calculation methods you are expected to know, from elasticity measures to macroeconomic indicators. Use it as a quick-reference guide while practising past paper questions.

掌握关键公式是 IGCSE OCR 经济学取得成功的基础。本手册汇编了你需要了解的所有定量关系和计算方法，从弹性度量到宏观经济指标。在练习历年真题时，可将它用作快速参考指南。

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 price of the good itself. It helps firms predict the effect of a price change on total revenue.

需求价格弹性衡量需求量对商品本身价格变动的反应程度。它帮助企业预测价格变动对总收益的影响。

The basic formula for PED uses percentage changes. Always express PED as a positive number (ignore the negative sign), because demand curves are downward sloping.

PED 的基本公式使用百分比变化。因为需求曲线向下倾斜，计算出的弹性值通常是负数，但通常将其表示为正数（忽略负号）。

PED = % Change in Quantity Demanded ÷ % Change in Price

需求价格弹性 = 需求量变动百分比 ÷ 价格变动百分比

To calculate a percentage change, use the original value as the denominator. For quantity demanded: %ΔQd = (Q₂ − Q₁) ÷ Q₁ × 100. For price: %ΔP = (P₂ − P₁) ÷ P₁ × 100.

计算百分比变化时，以原始数值作为分母。对于需求量：%ΔQd = (Q₂ − Q₁) ÷ Q₁ × 100。对于价格：%ΔP = (P₂ − P₁) ÷ P₁ × 100。

Interpreting the PED value determines whether demand is elastic, inelastic or unit elastic.

解读 PED 数值可以判断需求是富有弹性、缺乏弹性还是单位弹性。

PED Value	Demand is …	需求是…	Effect on Total Revenue (Price Rise)	对总收益的影响（价格上升）
> 1	Elastic	富有弹性	Revenue falls	总收益下降
< 1	Inelastic	缺乏弹性	Revenue rises	总收益上升
= 1	Unit elastic	单位弹性	Revenue unchanged	总收益不变
= 0	Perfectly inelastic	完全无弹性	Revenue rises by max	总收益最大幅度上升
∞	Perfectly elastic	完全有弹性	Revenue falls to zero (if price rises above market price)	总收益降至零（若价格高于市价）

Example: When a cinema increased ticket price from £8 to £10, tickets sold fell from 500 to 400. PED = [(400−500)/500 × 100] ÷ [(10−8)/8 × 100] = (−20%) ÷ 25% = 0.8. Demand is inelastic; the price rise will increase total revenue.

例题：某影院将票价从 8 英镑提高至 10 英镑，售票量从 500 张降至 400 张。PED = [(400−500)/500 × 100] ÷ [(10−8)/8 × 100] = (−20%) ÷ 25% = 0.8。需求缺乏弹性；提价会使总收益增加。

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2. Income Elasticity of Demand (YED) | 需求收入弹性

Income elasticity of demand measures how quantity demanded responds to a change in consumers’ income. It indicates whether a good is a normal good or an inferior good.

需求收入弹性衡量需求量对消费者收入变动的反应程度。它表明一种商品是正常品还是低档品。

YED = % Change in Quantity Demanded ÷ % Change in Income

需求收入弹性 = 需求量变动百分比 ÷ 收入变动百分比

The sign of YED is important. For normal goods, YED is positive; for inferior goods, YED is negative. Normal goods with YED > 1 are luxury goods, while those with 0 < YED < 1 are necessities.

YED 的正负号很重要。正常品的 YED 为正数；低档品的 YED 为负数。YED 大于 1 的正常品是奢侈品，而 YED 在 0 到 1 之间的正常品是必需品。

Example: If income rises by 10% and demand for organic vegetables rises by 15%, YED = 15% ÷ 10% = 1.5, indicating a luxury good. If demand for budget bread falls by 5%, YED = −5% ÷ 10% = −0.5, indicating an inferior good.

例题：如果收入增长 10%，有机蔬菜的需求增长 15%，则 YED = 15% ÷ 10% = 1.5，属于奢侈品。如果平价面包的需求下降 5%，则 YED = −5% ÷ 10% = −0.5，属于低档品。

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3. Cross Elasticity of Demand (XED) | 需求交叉弹性

Cross elasticity of demand measures the responsiveness of demand for one good (X) to a change in the price of another good (Y). It reveals whether goods are substitutes or complements.

需求交叉弹性衡量一种商品（X）的需求对另一种商品（Y）价格变动的反应程度。它揭示商品之间是替代品还是互补品。

XED = % Change in Quantity Demanded of Good X ÷ % Change in Price of Good Y

需求交叉弹性 = 商品 X 的需求量变动百分比 ÷ 商品 Y 的价格变动百分比

When XED is positive, the two goods are substitutes (e.g., tea and coffee). When XED is negative, they are complements (e.g., printers and ink cartridges). When XED is zero, the goods are unrelated.

当 XED 为正数时，两种商品互为替代品（例如茶和咖啡）。当 XED 为负数时，二者为互补品（例如打印机和墨盒）。当 XED 为零时，商品不相关。

The magnitude of XED indicates the strength of the relationship. A high positive XED suggests close substitutes; a highly negative XED suggests strong complements.

XED 的绝对值大小表明关系的强弱。高正数 XED 表明很接近的替代品；绝对值很大的负数 XED 表明很强的互补品。

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4. Price Elasticity of Supply (PES) | 供给价格弹性

Price elasticity of supply measures the responsiveness of quantity supplied to a change in price. It indicates how easily producers can change output when market price changes.

供给价格弹性衡量供给量对价格变动的反应程度。它表明当市场价格变动时，生产者调整产出的难易程度。

PES = % Change in Quantity Supplied ÷ % Change in Price

供给价格弹性 = 供给量变动百分比 ÷ 价格变动百分比

PES is always positive because of the law of supply. If PES > 1, supply is elastic; if PES < 1, supply is inelastic; if PES = 1, supply is unit elastic.

由于供给定律，PES 总是正数。如果 PES > 1，供给富有弹性；如果 PES < 1，供给缺乏弹性；如果 PES = 1，供给为单位弹性。

Key determinants of PES include the length of the production period, availability of spare capacity, and the level of stocks. Over longer time periods, supply is usually more elastic.

PES 的主要决定因素包括生产周期长度、闲置产能的可得性以及库存水平。在较长的时间段内，供给通常更具弹性。

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5. Costs, Revenue and Profit | 成本、收入与利润

A firm’s profit is the difference between total revenue and total costs. You must be able to calculate total revenue, total costs and profit using simple formulas.

企业的利润是总收益与总成本之间的差额。你必须能够使用简单公式计算总收益、总成本和利润。

Total Revenue (TR) = Price (P) × Quantity Sold (Q)

总收益 = 价格 × 销售量

Total Cost (TC) = Total Fixed Cost (TFC) + Total Variable Cost (TVC)

总成本 = 总固定成本 + 总可变成本

Profit = Total Revenue − Total Cost

利润 = 总收益 − 总成本

Average cost (unit cost) is calculated by dividing total cost by output. Average revenue equals price.

平均成本（单位成本）通过总成本除以产量计算得出。平均收益等于价格。

Average Cost (AC) = Total Cost ÷ Quantity

平均成本 = 总成本 ÷ 数量

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6. Productivity and Unit Cost | 生产率与单位成本

Productivity measures output per unit of input. Labour productivity is commonly tested. Improvements in productivity lower unit costs and can increase competitiveness.

生产率衡量每单位投入所能生产的产出。劳动生产率经常被考到。生产率的提高会降低单位成本，并可能增强竞争力。

Labour Productivity = Total Output ÷ Number of Workers (or Hours Worked)

劳动生产率 = 总产出 ÷ 劳动者人数（或工作小时数）

Unit cost refers to the cost of producing one unit of output. When productivity rises, unit cost tends to fall, assuming input costs remain constant.

单位成本指生产一单位产出所需的成本。当生产率提高时，在投入成本保持不变的条件下，单位成本往往会下降。

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7. Market Concentration Ratio | 市场集中度比率

A concentration ratio measures the combined market share of the largest firms in an industry. The N-firm concentration ratio is the sum of the market shares of the top N firms.

集中度比率衡量一个行业中最大几家企业的合计市场份额。N 企业集中度比率为最大 N 家企业的市场份额之和。

Concentration Ratio (CRn) = Sum of market shares of the n largest firms

集中度比率 (CRn) = 最大 n 家企业的市场份额之和

For example, CR5 = 70% means the five largest firms together control 70% of the market. Higher ratios suggest more concentrated markets and potentially less competition.

例如，CR5 = 70% 意味着最大的五家企业合计控制了 70% 的市场。比率越高，表明市场越集中，竞争可能越少。

You may be asked to calculate a concentration ratio from a table of market shares. Simply add the relevant percentages.

考试可能要求你根据市场份额表格计算集中度比率。只需将相关百分比相加即可。

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8. Unemployment Rate | 失业率

The unemployment rate is the proportion of the labour force that is willing and able to work but cannot find employment. It is a key macroeconomic performance indicator.

失业率是劳动力中愿意并能够工作但无法找到就业机会的人口所占的比例。它是一个关键的宏观经济绩效指标。

Unemployment Rate = (Number of Unemployed ÷ Labour Force) × 100

失业率 = （失业人数 ÷ 劳动力总数） × 100

The labour force includes all employed and unemployed people who are actively seeking work. It does not include students, retirees, or those who have stopped looking for a job.

劳动力包括所有就业人口以及正在积极寻找工作的失业人口。它不包括学生、退休人员或已停止寻找工作的人。

Example: If an economy has 30 million employed, 2 million unemployed, and 8 million economically inactive, the labour force is 32 million. Unemployment rate = (2m ÷ 32m) × 100 = 6.25%.

例题：如果一个经济体有 3000 万就业人口，200 万失业人口，以及 800 万非经济活动人口，则劳动力为 3200 万。失业率 = (200万 ÷ 3200万) × 100 = 6.25%。

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9. Inflation Rate (CPI) | 通货膨胀率（消费价格指数）

Inflation is the sustained increase in the general price level. The rate of inflation is most often measured using the Consumer Price Index (CPI).

通货膨胀是指一般物价水平的持续上升。通货膨胀率通常用消费价格指数（CPI）来衡量。

Inflation Rate = (CPI in Current Year − CPI in Previous Year) ÷ CPI in Previous Year × 100

通货膨胀率 = （当年 CPI − 上年 CPI） ÷ 上年 CPI × 100

The CPI tracks the price of a typical basket of goods and services consumed by households. A base year is chosen and set to an index of 100. Changes in the index reflect inflation.

CPI 追踪家庭消费的一篮子代表性商品和服务的价格。选择一个基年并将其指数定为 100。指数的变动反映了通货膨胀。

Example: If the CPI was 115 last year and is 120 this year, the inflation rate = (120 − 115) ÷ 115 × 100 = 4.35%.

例题：如果去年 CPI 为 115，今年为 120，则通货膨胀率 = (120 − 115) ÷ 115 × 100 = 4.35%。

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10. Gross Domestic Product (GDP) | 国内生产总值

GDP is the total value of all final goods and services produced within a country’s borders in a given period. You should understand how GDP per capita and economic growth are calculated.

GDP 是指在一国境内一段时期内生产的所有最终商品和服务的总价值。你应该了解如何计算人均 GDP 和经济增长率。

GDP per capita = Total GDP ÷ Population

人均 GDP = 国内生产总值 ÷ 人口数

Economic Growth Rate = (Real GDP in Current Year − Real GDP in Previous Year) ÷ Real GDP in Previous Year × 100

经济增长率 = （当年实际 GDP − 上年实际 GDP） ÷ 上年实际 GDP × 100

Real GDP is adjusted for inflation, while nominal GDP is not. Always use real GDP when measuring economic growth.

实际 GDP 已根据通货膨胀进行了调整，而名义 GDP 则没有。衡量经济增长时须始终使用实际 GDP。

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11. Exchange Rate Conversion | 汇率换算

Exchange rates express the value of one currency in terms of another. You must be able to convert amounts of money between currencies for examination questions.

汇率以一种货币表示另一种货币的价值。你必须能够在考题中完成不同货币之间的金额换算。

If 1 GBP = 1.25 USD, to convert from pounds to dollars you multiply the pound amount by 1.25. To convert from dollars to pounds, you divide the dollar amount by 1.25.

如果 1 英镑 = 1.25 美元，要将英镑兑换成美元，用英镑金额乘以 1.25。要将美元兑换成英镑，用美元金额除以 1.25。

Amount in foreign currency = Amount in domestic currency × Exchange Rate

外币金额 = 本币金额 × 汇率

An appreciation of the domestic currency means it buys more foreign currency; a depreciation means it buys less. These changes affect the relative prices of exports and imports.

本币升值意味着它能兑换更多的外币；本币贬值则意味着兑换更少。这些变化会影响出口和进口的相对价格。

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12. Real Income and Real Interest Rate | 实际收入与实际利率

Real values remove the effect of inflation and give a more accurate picture of purchasing power. Two common adjustments are real income and the real interest rate.

实际值剔除了通货膨胀的影响，能更准确地反映购买力。两种常见的调整是实际收入和实际利率。

Real Income = (Nominal Income ÷ CPI) × 100

实际收入 = （名义收入 ÷ CPI） × 100

If nominal income stays the same but CPI rises, real income falls. This occurs because each unit of currency now buys fewer goods and services.

如果名义收入保持不变而 CPI 上升，实际收入就会下降。这是因为每一单位货币现在能购买的商品和服务变少了。

The real interest rate accounts for the impact of inflation on the return from saving or the cost of borrowing. It is approximately the difference between the nominal interest rate and the inflation rate.

实际利率考虑了通货膨胀对储蓄回报或借款成本的影响。它大致等于名义利率与通货膨胀率之间的差额。

Real Interest Rate ≈ Nominal Interest Rate − Inflation Rate

实际利率 ≈ 名义利率 − 通货膨胀率

For precise calculations, a more accurate formula is sometimes used, but the simple subtraction is sufficient for IGCSE OCR. A positive real interest rate means the purchasing power of savings is growing.

有时会使用更精确的计算公式，但对于 IGCSE OCR 来说，简单相减就足够了。正的实际利率意味着储蓄的购买力在增长。

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