Elasticity Revision for GCSE CCEA Economics | 弹性 考点精讲

📚 Elasticity Revision for GCSE CCEA Economics | 弹性 考点精讲

Elasticity measures how responsive one economic variable is to a change in another. In GCSE CCEA Economics, you are required to understand price elasticity of demand and supply, income elasticity of demand, and cross elasticity of demand. These concepts help explain how markets react to changes in price, incomes, and the prices of related goods, and they are essential for analysing business decisions and government policy.

弹性衡量一个经济变量对另一个经济变量变化的反应程度。在 CCEA GCSE 经济学中，你需要理解需求价格弹性、供给价格弹性、需求收入弹性以及需求交叉弹性。这些概念有助于解释市场如何对价格、收入和相关商品价格的变化做出反应，对于分析企业决策和政府政策至关重要。

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1. What is Elasticity? | 什么是弹性？

Elasticity is a measure of sensitivity. If a small change in price, income, or another variable causes a large proportional change in quantity demanded or supplied, we say the relationship is elastic. If the quantity changes very little, it is inelastic.

弹性是一种敏感度的衡量指标。如果价格、收入或其他变量的微小变化导致需求量或供给量发生较大比例的变化，我们就说这种关系是有弹性的（富有弹性）。如果数量变化很小，则是缺乏弹性的（无弹性）。

Elasticity is always calculated as the percentage change in one variable divided by the percentage change in another. This makes it a unit‑free measure, allowing comparisons across different goods and markets.

弹性始终以某一变量的变动百分比除以另一变量的变动百分比来计算。这使得弹性成为一个无单位的衡量指标，便于在不同商品和市场之间进行比较。

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

Price elasticity of demand (PED) measures how much the quantity demanded of a good responds to a change in its own price. The formula is:

需求价格弹性 (PED) 衡量一种商品的需求量对其自身价格变化的反应程度。其计算公式为：

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

This is often written as:

通常也写作：

PED = (ΔQd / Qd) ÷ (ΔP / P)

where ΔQd is the change in quantity demanded, Qd is the original quantity, ΔP is the change in price, and P is the original price. A negative value is expected because of the law of demand, but in GCSE we often ignore the minus sign and focus on the absolute value.

其中 ΔQd 为需求量的变动，Qd 为最初的需求量，ΔP 为价格的变动，P 为最初的价格。由于需求定律，PED 通常为负值，但在 GCSE 中我们通常忽略负号，专注于绝对值。

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3. Interpreting PED Values | PED 数值的解读

The absolute value of PED tells us whether demand is elastic or inelastic. The key categories are:

PED 的绝对值告诉我们需求是富有弹性还是缺乏弹性。主要分类如下：

PED Value	Classification | 分类	Meaning | 含义
PED > 1	Elastic | 富有弹性	Quantity demanded changes by a larger percentage than price. | 需求量变动的百分比大于价格变动的百分比。
PED < 1	Inelastic | 缺乏弹性	Quantity demanded changes by a smaller percentage than price. | 需求量变动的百分比小于价格变动的百分比。
PED = 1	Unitary elastic | 单位弹性	Quantity demanded changes by exactly the same percentage as price. | 需求量变动的百分比与价格变动的百分比完全相等。
PED = ∞	Perfectly elastic | 完全弹性	Any price rise causes quantity demanded to fall to zero. | 任何价格上涨都会使需求量降为零。
PED = 0	Perfectly inelastic | 完全无弹性	Quantity demanded does not change at all when price changes. | 价格变化时需求量完全不变。

Remember that perfectly elastic demand is shown by a horizontal demand curve, while perfectly inelastic demand is shown by a vertical demand curve.

请记住，完全弹性的需求表现为一条水平的需求曲线，而完全无弹性的需求表现为一条垂直的需求曲线。

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4. PED and Total Revenue | PED 与总收入

Total revenue (TR) is the amount a firm receives from selling its product, calculated as price × quantity. The relationship between PED and total revenue is crucial for business pricing decisions.

总收入 (TR) 是企业销售产品所获得的金额，计算公式为 价格 × 数量。PED 与总收入之间的关系对于企业的定价决策至关重要。

If demand is elastic (PED > 1), a price increase will cause a proportionally larger fall in quantity demanded, so total revenue will decrease. A price cut, on the other hand, will increase total revenue.

如果需求富有弹性 (PED > 1)，价格上涨会导致需求量以更大的比例下降，因此总收入会减少。相反，降价会增加总收入。

If demand is inelastic (PED < 1), a price increase leads to a smaller percentage fall in quantity demanded, so total revenue will rise. A price cut will reduce total revenue.

如果需求缺乏弹性 (PED < 1)，价格上涨导致需求量下降的百分比较小，因此总收入会上升。降价则会减少总收入。

If demand is unitary elastic (PED = 1), any price change leaves total revenue unchanged, because the percentage change in price is exactly offset by the percentage change in quantity demanded.

如果需求是单位弹性 (PED = 1)，任何价格变动都不会改变总收入，因为价格变动的百分比恰好被需求量变动的百分比所抵消。

This relationship is often tested in multiple‑choice questions and data‑response tasks.

这种关系经常在选择题和数据分析题中考查。

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5. Determinants of PED | 影响 PED 的因素

Several factors determine whether demand for a good is elastic or inelastic. The main factors are:

决定一种商品需求是富有弹性还是缺乏弹性的因素有以下几个主要方面：

Number and closeness of substitutes: Goods with many close substitutes tend to have elastic demand because consumers can easily switch if the price rises. For example, different brands of soft drinks are highly substitutable.

替代品的数量和相似程度：拥有许多相近替代品的商品，其需求往往富有弹性，因为价格上涨时消费者很容易转向其他商品。例如，不同品牌的软饮料具有很高的替代性。

Necessity versus luxury: Necessities (such as basic food or life‑saving medicines) tend to have inelastic demand, while luxury goods (such as designer clothing or holidays) are more elastic.

必需品与奢侈品：必需品（如基本食品或救命药品）的需求通常缺乏弹性，而奢侈品（如名牌服装或假期）则更富有弹性。

Proportion of income spent on the good: Goods that take up a large share of a consumer’s income, such as cars or furniture, tend to have elastic demand. Inexpensive items like matches or salt tend to be inelastic.

占收入的比例：在消费者收入中占比较大的商品（如汽车或家具），其需求往往富有弹性。而像火柴或食盐这类廉价商品的弹性则很小。

Time period: Demand tends to be more elastic in the long run because consumers have more time to find alternatives or adjust their behaviour. In the short run, demand is often inelastic.

时间因素：长期内需求往往更富有弹性，因为消费者有更多时间寻找替代品或调整其行为。短期内，需求通常缺乏弹性。

Addiction and habit: Products like cigarettes or coffee often have inelastic demand because consumers find it hard to reduce consumption even when price rises.

成瘾和习惯：香烟或咖啡等产品通常需求缺乏弹性，因为即使价格上涨，消费者也很难减少消费。

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6. Price Elasticity of Supply (PES) Formula | 供给价格弹性公式

Price elasticity of supply (PES) measures the responsiveness of quantity supplied to a change in the good’s own price. The formula is:

供给价格弹性 (PES) 衡量供给量对商品自身价格变化的反应程度。计算公式为：

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

This is written as:

也可以写作：

PES = (ΔQs / Qs) ÷ (ΔP / P)

where ΔQs is the change in quantity supplied. Unlike PED, PES is usually positive because a higher price encourages firms to supply more.

其中 ΔQs 为供给量的变动。与 PED 不同，PES 通常为正值，因为更高的价格会激励企业增加供给。

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7. Interpreting PES Values and Determinants | PES 数值解读与决定因素

PES is interpreted in a similar way to PED, but the sign is positive. The key categories are:

PES 的解读方式与 PED 相似，但符号为正。主要分类如下：

PES Value	Classification | 分类	Meaning | 含义
PES > 1	Elastic | 富有弹性	Quantity supplied changes by a larger percentage than price. | 供给量变动的百分比大于价格变动的百分比。
PES < 1	Inelastic | 缺乏弹性	Quantity supplied changes by a smaller percentage than price. | 供给量变动的百分比小于价格变动的百分比。
PES = 1	Unitary elastic | 单位弹性	Quantity supplied changes by the same percentage as price. | 供给量变动的百分比与价格变动的百分比相同。
PES = 0	Perfectly inelastic | 完全无弹性	Quantity supplied does not respond to price changes (e.g., fixed supply of tickets for a stadium event).

The main determinants of PES are:

PES 的主要决定因素包括：

Time period: Supply is more elastic in the long run, as firms can expand capacity, hire more workers, and invest in new technology. In the short run, supply is often inelastic because at least one factor of production is fixed.

时间因素：长期内供给更加富有弹性，因为企业可以扩大产能、雇用更多工人并投资新技术。短期内，供给通常缺乏弹性，因为至少有一种生产要素是固定的。

Spare capacity: If a firm has idle machinery or unused factory space, it can increase output quickly when price rises – supply will be elastic. Firms running at full capacity face inelastic supply.

闲置产能：如果企业有闲置的机器或未使用的厂房空间，就能在价格上涨时迅速增加产量，此时供给富有弹性。满负荷运转的企业则面临缺乏弹性的供给。

Availability of stocks: Goods that can be stored easily (e.g., canned food, books) tend to have more elastic supply, as firms can release stocks when price rises.

库存的可得性：容易储存的商品（如罐头食品、书籍）供给往往更富有弹性，因为企业可以在价格上涨时释放库存。

Mobility of factors of production: If resources can be moved quickly from one use to another, supply is more elastic.

生产要素的流动性：如果资源能够迅速从一种用途转移到另一种用途，供给就更加富有弹性。

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

Income elasticity of demand (YED) measures how quantity demanded changes in response to a change in consumers’ income. The formula is:

需求收入弹性 (YED) 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 tells us whether a good is a normal good or an inferior good.

YED 告诉我们一种商品是正常品还是劣等品。

Normal goods have a positive YED. Demand rises when income rises. Within normal goods:

• If YED > 1, the good is a luxury (e.g., fine dining, sports cars). Demand increases by a larger percentage than income.
• If 0 < YED < 1, the good is a necessity (e.g., basic food, toothpaste). Demand increases by a smaller percentage than income.

正常品的 YED 为正。收入增加时需求上升。在正常品内部：

• 如果 YED > 1，该商品为奢侈品（如高级餐厅、跑车）。需求增加的百分比大于收入增加的百分比。
• 如果 0 < YED < 1，该商品为必需品（如基本食物、牙膏）。需求增加的百分比小于收入增加的百分比。

Inferior goods have a negative YED (YED < 0). As income rises, consumers buy less of these goods, switching to better alternatives (e.g., supermarket‑own‑brand bread, bus travel).

劣等品的 YED 为负 (YED < 0)。随着收入增加，消费者购买这类商品的数量减少，转而选择更好的替代品（如超市自有品牌面包、公共汽车出行）。

Businesses use YED to forecast how demand will change as the economy grows or during a recession. For example, producers of luxury goods benefit more in a boom, while producers of inferior goods may see higher demand in a downturn.

企业利用 YED 来预测需求在经济增长或衰退期间将如何变化。例如，奢侈品生产商在经济繁荣时获益更多，而劣等品生产商在经济低迷时可能看到需求上升。

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

Cross elasticity of demand (XED) measures the responsiveness of demand for one good (Good A) to a change in the price of another good (Good B). The formula is:

需求交叉弹性 (XED) 衡量一种商品（A 商品）的需求对另一种商品（B 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

The sign of XED tells us about the relationship between the two goods.

XED 的符号告诉我们两种商品之间的关系。

Substitutes have a positive XED. If the price of Coca‑Cola rises, the demand for Pepsi increases – consumers switch to the substitute. The larger the positive value, the closer the substitutes.

替代品的 XED 为正。如果可口可乐的价格上涨，百事可乐的需求就会增加——消费者转向替代品。正值越大，表示替代品越接近。

Complements have a negative XED. If the price of printers rises, the demand for ink cartridges falls, because the two goods are used together. The more negative the XED, the stronger the complementarity.

互补品的 XED 为负。如果打印机的价格上涨，墨盒的需求就会下降，因为这两种商品需要一起使用。XED 越负，互补关系越强。

Unrelated goods have an XED of or close to zero. A change in the price of shoes has no effect on the demand for oranges.

不相关商品的 XED 为零或接近于零。鞋子价格的变化对橙子的需求没有影响。

XED is particularly useful for firms when predicting the impact of competitors’ pricing strategies or when deciding on bundled offers for complementary products.

XED 对于企业预测竞争对手定价策略的影响或决定互补产品的捆绑销售时特别有用。

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10. Common Mistakes and Exam Tips | 常见错误与考试技巧

Mistake 1: Confusing the sign of PED with the sign of XED. Remember that PED is usually negative (but you use the absolute value), while XED can be positive or negative depending on the relationship.

错误 1：混淆 PED 的符号与 XED 的符号。请记住，PED 通常为负值（但考试中使用绝对值），而 XED 根据商品关系可正可负。

Mistake 2: Assuming that a steep demand curve always means inelastic demand. Elasticity varies along a straight-line demand curve – it is not the same as slope.

错误 2：认为陡峭的需求曲线总是意味着需求缺乏弹性。弹性沿一条直线需求曲线发生变化——弹性并不等同于斜率。

Mistake 3: Forgetting to use percentage changes when calculating elasticity. Always work with percentages, not absolute numbers.

错误 3：计算弹性时忘记使用百分比变化。务必使用百分比，而不是绝对数值。

Mistake 4: Mixing up YED and XED. YED relates to income changes, while XED relates to the price of another good. Be precise in your definitions.

错误 4：混淆 YED 和 XED。YED 与收入变化相关，而 XED 与另一商品的价格相关。定义要准确。

Exam tip: In data‑response questions, practise calculating elasticity from given figures and then applying the value to explain the effect on total revenue or market behaviour. Always state the formula, show your workings, and give a precise interpretation.

考试技巧：在数据分析题中，练习根据给定数据计算弹性，然后运用该数值解释对总收入或市场行为的影响。始终写明公式，展示计算过程，并给出准确的解释。

Published by TutorHao | Economics Revision Series | aleveler.com

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