A-Level Economics: Elasticity Key Concepts | A-Level 经济：弹性 考点精讲

📚 A-Level Economics: Elasticity Key Concepts | A-Level 经济：弹性 考点精讲

Welcome to this comprehensive revision guide on elasticity for A-Level Economics. Elasticity is a fundamental concept that explains how economic agents respond to changes in market conditions. It measures the sensitivity of one variable, such as quantity demanded or supplied, to changes in another, such as price or income. Mastering elasticity is essential for understanding consumer behaviour, business pricing strategies, government taxation, and the effectiveness of economic policies.

欢迎阅读这篇针对 A-Level 经济学的弹性考点精讲。弹性是一个基本概念，解释经济主体如何对市场条件的变化作出反应。它衡量一个变量（如需求量或供给量）对另一个变量（如价格或收入）变化的敏感程度。掌握弹性对于理解消费者行为、企业定价策略、政府税收以及经济政策的有效性至关重要。

1. What Is Elasticity? | 什么是弹性？

Elasticity is defined as the ratio of the percentage change in one variable to the percentage change in another variable. In economics we use it to quantify how much quantity demanded or supplied stretches or shrinks when a determinant changes.

弹性定义为一个变量的百分比变化与另一个变量的百分比变化的比率。在经济学中我们用它来量化当某个决定因素变化时，需求量或供给量会“拉伸”或“收缩”多少。

The general formula is: Elasticity = %Δ in dependent variable ÷ %Δ in independent variable. For demand, the dependent variable is quantity demanded (Qd), and the independent variable can be own price, income, or another good’s price.

一般公式为：弹性 = 因变量的百分比变化 ÷ 自变量的百分比变化。对于需求，因变量是需求量 (Qd)，自变量可以是商品自身价格、收入或其他商品价格。

Elasticity is always a unit-free number because we divide two percentage changes. This allows economists to compare responsiveness across different goods and markets.

弹性总是一个无单位的数值，因为我们将两个百分比变化相除。这使得经济学家能够比较不同商品和市场的反应程度。

2. 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 tells us how much more or less consumers will buy when the price rises or falls.

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。它告诉我们当价格上升或下降时消费者会多买还是少买。

PED = %ΔQ_d ÷ %ΔP

PED = 需求量变动百分比 ÷ 价格变动百分比

Because the law of demand states that price and quantity demanded move in opposite directions, PED is always negative. However, by convention we often drop the minus sign and refer to the absolute value |PED| in our analysis. A PED of −1.5, for example, is treated as an elastic demand with an absolute value of 1.5.

因为需求定律指出价格与需求量反向变动，PED 总是负值。然而，按惯例我们通常省略负号而在分析中使用绝对值 |PED|。例如，PED 为 −1.5 视为弹性需求，绝对值为 1.5。

3. Calculating PED & Interpreting Values | 计算 PED 与解读数值

To calculate PED, first work out the two percentage changes. Percentage change = (New − Old) / Old × 100%.

要计算 PED，先求出两个百分比变化。百分比变化 = (新值 − 旧值) / 旧值 × 100%。

Example: A cinema raises the ticket price from £8 to £10, and the number of tickets sold per day falls from 500 to 400. The %ΔP = (10 − 8)/8 × 100 = 25%. The %ΔQ_d = (400 − 500)/500 × 100 = −20%. Thus PED = −20% ÷ 25% = −0.8. The absolute value is 0.8, indicating inelastic demand.

示例：一家影院将票价从 8 英镑提高到 10 英镑，每日售票量从 500 张降至 400 张。%ΔP = (10−8)/8×100 = 25%。%ΔQ_d = (400−500)/500×100 = −20%。因此 PED = −20% ÷ 25% = −0.8。绝对值为 0.8，表明需求缺乏弹性。

The table below summarises the five categories of PED based on absolute values.

下表根据绝对值总结了 PED 的五种分类。

An elastic demand means consumers are very responsive to price changes, while inelastic demand implies quantity demanded changes only a little when price changes.

富有弹性意味着消费者对价格变化非常敏感，而缺乏弹性则意味着价格变化时需求量仅小幅变动。

Perfectly inelastic demand shows a situation where the same quantity is bought regardless of price; perfectly elastic demand means that consumers will buy nothing if price rises even slightly above the market price.

完全无弹性需求表示无论价格如何，购买量都不变；完全弹性需求意味着如果价格略微高于市价，消费者将完全不购买。

4. PED and Total Revenue | PED 与总收益

Total revenue (TR) is the amount of money a firm receives from sales: TR = Price × Quantity. The relationship between PED and TR is a powerful tool for pricing decisions.

总收益 (TR) 是企业从销售中获得的金额：TR = 价格 × 数量。P

Published by TutorHao | A-Level Economics Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）