GCSE OCR Economics: Elasticity | GCSE OCR 经济：弹性 考点精讲

📚 GCSE OCR Economics: Elasticity | GCSE OCR 经济：弹性 考点精讲

Elasticity measures how much one variable changes in response to a change in another variable. In GCSE Economics, understanding elasticity helps explain how markets react to shifts in price, income, or the prices of other goods. It is a fundamental concept for analysing consumer and producer behaviour, and for evaluating the impact of government policies such as taxes and subsidies.

弹性衡量一个变量对另一个变量变化的反应程度。在 GCSE 经济学中，理解弹性有助于解释市场如何对价格、收入或其他商品价格的变化做出反应。这是分析消费者和生产者行为以及评估税收和补贴等政府政策影响的基本概念。

1. What is Elasticity? | 什么是弹性？

Elasticity is a numerical measure of responsiveness. When we talk about elasticity in economics, we usually compare the percentage change in one variable (e.g. quantity demanded) with the percentage change in another variable (e.g. price). The result is the elasticity coefficient, which tells us whether the relationship is elastic, inelastic, or unit elastic.

弹性是一个衡量反应程度的数值。我们在经济学中讨论弹性时，通常比较一个变量（例如需求量）的百分比变化与另一个变量（例如价格）的百分比变化。得出的结果是弹性系数，它告诉我们这种关系是富有弹性、缺乏弹性还是单位弹性。

If the magnitude of the elasticity coefficient is greater than 1, the relationship is elastic: a given percentage change in one variable causes a larger percentage change in the other. If the coefficient is less than 1, it is inelastic: the percentage change in one variable leads to a smaller percentage change in the other. A coefficient of exactly 1 indicates unit elasticity, meaning the percentage changes are equal.

如果弹性系数的绝对值大于 1，关系就是富有弹性的：一个变量的特定百分比变化会引起另一个变量更大百分比的变动。如果系数小于 1，就是缺乏弹性：一个变量的百分比变化导致另一个变量较小百分比的变动。系数恰好为 1 则表示单位弹性，即两个百分比变化相等。

2. Price Elasticity of Demand (PED) | 需求价格弹性 (PED)

Price elasticity of demand measures how much the quantity demanded of a good changes when its price changes. The formula for PED is:

需求价格弹性衡量一种商品的需求量对其价格变化的反应程度。PED 的公式为：

PED = (% change in quantity demanded) ÷ (% change in price)

For example, if a 10% rise in the price of a product leads to a 20% fall in quantity demanded, PED = -20% / 10% = -2.0. The negative sign is often ignored when discussing elasticity values, so we refer to its absolute value. Here, PED = 2, which is elastic.

例如，如果某产品价格上升 10%，导致需求量下降 20%，则 PED = -20% / 10% = -2.0。在讨论弹性数值时通常忽略负号，所以我们指的是其绝对值。此处 PED = 2，为富有弹性。

If PED > 1, demand is price elastic. A price cut will increase total revenue because the percentage increase in quantity sold outweighs the percentage fall in price. If PED < 1, demand is price inelastic. A price rise will increase total revenue, as the drop in quantity demanded is proportionally smaller than the price increase. If PED = 1, total revenue stays the same when price changes.

如果 PED > 1，需求富有价格弹性。降价会增加总收入，因为销售量上升的百分比大于价格下降的百分比。如果 PED < 1，需求缺乏价格弹性。提价会增加总收入，因为需求量的降幅在比例上小于价格的涨幅。如果 PED = 1，价格变动时总收入保持不变。

3. Determinants of PED | 需求价格弹性的决定因素

Several factors influence whether demand for a product is elastic or inelastic. Understanding these helps businesses set pricing strategies and predict the effect of taxes.

有几个因素影响一种产品的需求是富有弹性还是缺乏弹性。理解这些因素有助于企业制定定价策略并预测税收的影响。

• Availability of substitutes: Goods with many close substitutes tend to have elastic demand, as consumers can easily switch if the price rises. Goods with few substitutes are more inelastic.

  替代品的可得性：拥有许多近似替代品的商品需求往往富有弹性，因为价格上涨时消费者很容易转向其他商品。替代品少的商品更缺乏弹性。

• Luxury vs necessity: Necessities (e.g. basic food, water) usually have inelastic demand because people need them regardless of price. Luxuries (e.g. designer handbags) have elastic demand.

  奢侈品 vs 必需品：必需品（如基本食物、水）通常需求缺乏弹性，因为无论价格高低人们都需要它们。奢侈品（如名牌手袋）需求富有弹性。

• Proportion of income spent: If a good takes up a large share of a consumer’s budget, demand tends to be elastic (e.g. a car). If it is a small share, demand tends to be inelastic (e.g. a box of matches).

  支出占收入的比例：如果一种商品在消费者预算中占比较大，需求往往富有弹性（例如汽车）。占比较小则需求往往缺乏弹性（例如一盒火柴）。

• Time period: In the short run, demand is often more inelastic because consumers may find it difficult to change habits immediately. Over time, demand becomes more elastic as they can adjust behaviour.

  时间周期：在短期内，需求往往更缺乏弹性，因为消费者可能难以立即改变习惯。随着时间的推移，他们可以调整行为，需求变得更有弹性。

• Addictiveness or habit: Products like tobacco or certain brands of coffee can have inelastic demand because consumers are less sensitive to price changes.

  成瘾性或习惯：像烟草或某些咖啡品牌这样的产品可能缺乏需求弹性，因为消费者对价格变化不那么敏感。

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

Price elasticity of supply measures how much the quantity supplied of a good changes when its market price changes. The formula for PES is:

供给价格弹性衡量一种商品的市场价格变化时，其供给量的反应程度。PES 的公式为：

PES = (% change in quantity supplied) ÷ (% change in price)

PES is almost always positive because a price increase normally makes it more profitable to produce and supply more. If PES > 1, supply is elastic: producers can increase output significantly when price rises. If PES < 1, supply is inelastic: quantity supplied changes by a smaller percentage than the price change. Unit elastic supply (PES = 1) means price and quantity supplied change by the same proportion.

PES 几乎总是正值，因为价格上涨通常使生产和供应更多产品更有利可图。如果 PES > 1，供给富有弹性：价格上涨时生产者可以大幅增加产量。如果 PES < 1，供给缺乏弹性：供给量的变化百分比小于价格的变动百分比。单位弹性供给 (PES = 1) 意味着价格和供给量以相同比例变化。

5. Determinants of PES | 供给价格弹性的决定因素

The ability of firms to increase output in response to a price rise depends on several key factors.

企业对价格上涨做出反应并增加产量的能力取决于几个关键因素。

• Availability of stocks: If firms hold large inventories of finished goods, they can quickly supply more to the market when price rises, making supply more elastic. If stocks are low, supply is less elastic.

  库存可得性：如果企业持有大量成品库存，它们可以在价格上涨时迅速向市场供应更多产品，从而使供给更富弹性。如果库存低，供给弹性就较小。

• Spare production capacity: Firms operating below full capacity can expand output easily, leading to elastic supply. When capacity is fully used, supply is inelastic in the short run.

  闲置产能：在未满负荷运营的企业可以轻松扩大产出，导致供给富有弹性。当产能被完全利用时，短期内供给缺乏弹性。

• Time period: In the short run, at least one factor of production is fixed, so supply is often inelastic. In the long run, all factors are variable, enabling more elastic supply.

  时间周期：在短期内，至少有一种生产要素是固定的，因此供给往往缺乏弹性。长期中，所有要素都可变，使供给更富弹性。

• Ease of entry into the market: If new firms can enter the industry quickly when prices rise, supply will be more elastic. High barriers to entry make supply inelastic.

  进入市场的难易度：如果新企业在价格上涨时可以迅速进入该行业，供给将更富弹性。高进入壁垒使供给缺乏弹性。

• Complexity of production: Goods that require specialised skills or long production times (e.g. handcrafted furniture) tend to have relatively inelastic supply compared to goods produced quickly (e.g. bottled water).

  生产复杂性：需要专业技能或长生产周期的商品（如手工家具）与生产迅速的商品（如瓶装水）相比，供给通常相对缺乏弹性。

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

Income elasticity of demand measures how quantity demanded responds to a change in consumers’ income. The formula is:

需求收入弹性衡量需求量对消费者收入变化的反应程度。公式为：

YED = (% change in quantity demanded) ÷ (% change in income)

YED can be positive or negative. For most goods, as income rises, demand rises, so YED is positive. If YED > 1, the good is a luxury: demand grows faster than income. If 0 < YED < 1, the good is a necessity: demand rises but at a slower rate than income. If YED is negative, the good is an inferior good: demand falls as income rises (e.g. cheaper own-brand products).

YED 可以是正也可以是负。对大多数商品而言，收入增加需求增加，因此 YED 为正。如果 YED > 1，该商品是奢侈品：需求增长快于收入。如果 0 < YED < 1，该商品是必需品：需求增长但慢于收入。如果 YED 为负，该商品是劣质品：收入上升时需求下降（例如廉价自有品牌产品）。

Firms use YED to forecast how demand for their products will change during economic growth or recession. For example, sellers of luxury cars will expect strong sales growth when the economy is booming (high positive YED), while producers of basic food items will see little change.

企业利用 YED 预测在经济繁荣或衰退时产品需求将如何变化。例如，豪车经销商在经济繁荣时预期销售强劲增长（高正数 YED），而基本食品生产商几乎不会看到什么变化。

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

Cross elasticity of demand measures how the quantity demanded of one good changes when the price of another good changes. The formula is:

需求交叉弹性衡量一种商品的需求量对另一种商品价格变化的反应程度。公式为：

XED = (% change in quantity demanded of good A) ÷ (% change in price of good B)

If XED is positive, the two goods are substitutes. A rise in the price of good B will increase demand for good A (e.g. if the price of coffee rises, demand for tea may increase). If XED is negative, the goods are complements. A rise in the price of good B reduces demand for good A (e.g. if the price of printers goes up, demand for printer ink may fall). If XED is close to zero, the two goods are unrelated.

如果 XED 为正，这两种商品是替代品。商品 B 的价格上涨会增加对商品 A 的需求（例如，咖啡涨价，对茶的需求可能增加）。如果 XED 为负，这两种商品是互补品。商品 B 的价格上涨会减少对商品 A 的需求（例如，打印机涨价，对墨盒的需求可能下降）。如果 XED 接近零，这两种商品不相关。

Knowledge of XED helps firms anticipate the impact of competitors’ pricing strategies and make decisions about product ranges. It also helps governments assess the consequences of taxing certain goods—for instance, taxing sugary drinks may boost demand for diet drinks (a substitute).

了解 XED 有助于企业预判竞争对手定价策略的影响并做出产品线决策。它还有助于政府评估对某些商品征税的后果——例如，对含糖饮料征税可能会增加对无糖饮料（替代品）的需求。

8. Elasticity and Total Revenue | 弹性与总收入

The relationship between PED and total revenue is crucial for business pricing decisions. Total revenue (TR) is price multiplied by quantity sold: TR = P × Q.

PED 与总收入之间的关系对于企业的定价决策至关重要。总收入 (TR) 等于价格乘以销售量：TR = P × Q。

When demand is elastic (PED > 1), a price cut increases total revenue, because the proportional rise in quantity demanded outweighs the fall in price. A price rise will lower total revenue. When demand is inelastic (PED < 1), a price rise increases total revenue, as the fall in quantity is proportionally smaller than the price increase. A price cut would reduce total revenue. When demand is unit elastic (PED = 1), total revenue remains constant regardless of price changes.

当需求富有弹性 (PED > 1)，降价会增加总收入，因为需求量增加的幅度超过了价格下降的幅度。提价则会降低总收入。当需求缺乏弹性 (PED < 1)，提价会增加总收入，因为需求量减少的幅度在比例上小于价格上涨的幅度。降价则会减少总收入。当需求为单位弹性 (PED = 1)，无论价格如何变化，总收入保持不变。

This helps explain why governments often place high taxes on inelastic goods (e.g. tobacco, alcohol, fuel). The tax raises the price, but quantity demanded falls relatively little, generating significant tax revenue.

这有助于解释为什么政府经常对缺乏弹性的商品（如烟草、酒精、燃料）征收高额税。税收抬高价格，但需求量下降相对较少，从而产生了可观的税收收入。

9. Elasticity and Government Intervention | 弹性与政府干预

Governments use elasticity concepts when designing taxes and subsidies. Indirect taxes (e.g. excise duties) are more effective in raising revenue when demand is inelastic. For example, a tax on petrol will not greatly reduce consumption—it will simply generate a lot of tax revenue. Conversely, if demand is elastic, a tax might drastically reduce quantity consumed, leading to less revenue and potentially higher unemployment in that industry.

政府在制定税收和补贴政策时会运用弹性概念。当需求缺乏弹性时，间接税（如消费税）在增加收入方面更有效。例如，对汽油征税不会大幅减少消费——它只会产生大量税收。相反，如果需求富有弹性，税收可能大幅减少消费量，导致税收减少，并可能引发该行业更高的失业率。

Subsidies work in the opposite direction. A subsidy lowers the price paid by consumers and increases the quantity consumed. When demand is elastic, a small subsidy can lead to a large increase in quantity demanded, making subsidies more effective at encouraging output and consumption in such markets.

补贴的作用方向相反。补贴降低了消费者支付的价格并增加了消费量。当需求富有弹性时，一小笔补贴就能使需求量大幅增加，从而使补贴在此类市场中更有效地刺激产出和消费。

Additionally, price elasticity of supply affects the incidence of a tax. When supply is relatively inelastic, a greater share of a tax falls on producers. When supply is elastic, consumers bear more of the tax burden through higher prices.

此外，供给价格弹性影响税收负担的分配。当供给相对缺乏弹性时，更大比例的税收负担落在生产者身上。当供给富有弹性时，消费者通过更高的价格承担更多的税负。

10. Common Exam Tips | 常见考试技巧

For GCSE OCR Economics, you must be able to calculate elasticities using percent changes and interpret the coefficient. You should also be ready to apply elasticity to real-world contexts: why the demand for strawberries may be elastic, why housing supply tends to be inelastic in the short run, or how a smartphone company’s revenue changes when it reduces prices.

在 GCSE OCR 经济学中，你必须能够利用百分比变化计算各种弹性并解释系数。你还应准备将弹性应用于现实情境：为什么草莓的需求可能富有弹性，为什么住房供应在短期内通常缺乏弹性，或者智能手机公司降价时其收入如何变化。

Remember to explain the significance of numerical values. For example, a PED of -0.4 means demand is inelastic, so the firm can raise price to increase total revenue. When analysing data in the exam, link your answer to the determinants (substitutes, luxury/necessity, time) for a higher-level response.

记得解释数值的意义。例如，PED 为 -0.4 意味着需求缺乏弹性，因此企业可以提价以增加总收入。在考试中分析数据时，将你的答案与决定因素（替代品、奢侈品/必需品、时间）联系起来，以获得更高层级的回答。

Also, be prepared for multiple-choice questions that test the relationship between elasticity and total revenue, or that require identifying whether goods are substitutes or complements based on a given XED value. Diagrams, though not always compulsory, can help illustrate the steeper (inelastic) or flatter (elastic) demand curves.

另外，准备好应对测试弹性与总收入关系的选择题，或根据给定的 XED 值判断商品是替代品还是互补品的题目。图表虽然不是必须的，但可以帮助说明较陡（缺乏弹性）或较平缓（富有弹性）的需求曲线。

Finally, pay close attention to the sign of the coefficient. PED is typically negative (but often given in absolute terms), PES is positive, YED can be positive or negative, and XED can be positive or negative—each revealing different economic relationships.

最后，要特别注意系数的符号。PED 通常为负（但常以绝对值给出），PES 为正，YED 可正可负，XED 可正可负——各自揭示了不同的经济关系。

Published by TutorHao | GCSE Economics Revision Series | aleveler.com

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