📚 Deadweight Loss | 无谓损失
In A‑Level Economics, deadweight loss refers to the loss of economic efficiency that occurs when the equilibrium for a good or service is not achieved or is not achievable. It represents the total surplus – the sum of consumer and producer surplus – that is lost due to market distortions such as taxes, subsidies, price controls, monopoly power, and trade barriers. Understanding deadweight loss is essential for evaluating the welfare effects of government policies and market structures.
在A‑Level经济学中，无谓损失是指当商品或服务的市场均衡无法达到时所产生的经济效率损失。它代表了由于税收、补贴、价格管制、垄断力量或贸易壁垒等市场扭曲而损失的总剩余——即消费者剩余与生产者剩余之和。理解无谓损失对于评估政府政策与市场结构的福利效应至关重要。
1. Consumer Surplus, Producer Surplus, and Total Surplus | 消费者剩余、生产者剩余与总剩余
Consumer surplus is the difference between the maximum price consumers are willing to pay and the market price they actually pay. It measures the net benefit consumers gain from purchasing a good.
消费者剩余是消费者愿意支付的最高价格与实际支付的市场价格之间的差额，衡量消费者从购买商品中获得的净收益。
Producer surplus is the difference between the market price firms receive and the minimum price they are willing to accept. It captures the net benefit producers receive from selling a good.
生产者剩余是企业收到的市场价格与其愿意接受的最低价格之间的差额，体现了生产者从销售商品中获得的净收益。
Total surplus is the sum of consumer surplus and producer surplus. In a free competitive market at equilibrium, total surplus is maximised, and there is no deadweight loss.
总剩余是消费者剩余与生产者剩余之和。在自由竞争市场的均衡点，总剩余达到最大，不存在无谓损失。
2. What is Deadweight Loss? | 什么是无谓损失？
Deadweight loss (also called excess burden) is the reduction in total surplus that results from a market not being in competitive equilibrium. It is typically represented graphically as a triangle between the supply and demand curves, formed by the lost transactions that would have occurred at the equilibrium quantity.
无谓损失（也称超额负担）是指市场未处于竞争均衡时造成的总剩余减少，通常在图形上表示为供给曲线与需求曲线之间的一个三角形，对应于均衡数量下本应发生但未能发生的交易。
Deadweight loss arises because some mutually beneficial exchanges do not take place. The quantity traded falls below (or rises above, in the case of overproduction) the socially optimal level, causing a welfare loss that is borne by neither consumers nor producers – it simply vanishes from the economy.
无谓损失的产生是由于一些互惠互利的交易未能发生。交易量低于（或在生产过剩时高于）社会最优水平，造成既非消费者也非生产者承担的福利损失——它直接在经济中消失。
3. Deadweight Loss from Indirect Taxes | 间接税造成的无谓损失
When the government imposes an indirect tax on a good, the supply curve shifts vertically upwards by the amount of the tax. This raises the price paid by consumers, lowers the price received by producers, and reduces the equilibrium quantity.
当政府对商品征收间接税时，供给曲线向上垂直移动税额的大小。这提高了消费者支付的价格，降低了生产者收到的价格，并减少了均衡数量。
eadweight loss is the triangle between the original equilibrium quantity and the new, lower quantity, reflecting the lost consumer and producer surplus that is not captured as tax revenue.
政府征收的税收收入用矩形（每单位税额 × 新的数量）表示。无谓损失是原均衡数量与新较低数量之间的三角形，反映了未被税收收入捕获的、损失的消费者剩余与生产者剩余。
Both consumer surplus and producer surplus shrink. The sum of the tax revenue and the deadweight loss equals the total surplus loss compared to the free‑market equilibrium.
消费者剩余和生产者剩余均减少。税收收入与无谓损失之和等于相对于自由市场均衡所损失的总剩余。
4. Elasticity and the Size of Deadweight Loss | 弹性与无谓损失的大小
The magnitude of deadweight loss from a tax depends on the price elasticities of demand and supply. The more elastic demand (or supply) is, the larger the reduction in quantity for a given tax, and hence the greater the deadweight loss.
税收造成的无谓损失大小取决于需求与供给的价格弹性。需求（或供给）弹性越大，在既定的税额下数量减少越多，无谓损失就越大。
| Elasticity Scenario | Effect on DWL |
|---|---|
| Relatively elastic demand | Larger DWL – consumers reduce quantity sharply |
| Relatively inelastic demand | Smaller DWL – quantity falls only slightly |
| Relatively elastic supply | Larger DWL – producers cut output significantly |
| Relatively inelastic supply | Smaller DWL – output reduction is modest |
This relationship explains why governments often levy heavy taxes on goods with inelastic demand (e.g. cigarettes, alcohol) to raise revenue without causing a large deadweight loss.
这种关系解释了为什么政府常常对需求缺乏弹性的商品（如香烟、酒精）征收高额税，以增加收入同时避免产生较大的无谓损失。
5. Deadweight Loss from Subsidies | 补贴造成的无谓损失
A subsidy shifts the supply curve downwards (or demand curve upwards, depending on the analysis). It lowers the price paid by consumers, raises the price received by producers, and increases the quantity above the free‑market equilibrium.
补贴使供给曲线向下移动（或需求曲线向上移动，视分析而定）。它降低了消费者支付的价格，提高了生产者收到的价格，并使数量增加到超过自由市场均衡水平。
While consumer surplus and producer surplus both increase, the government's subsidy expenditure exceeds the combined gain in surplus. The excess is the deadweight loss, shown as a triangle representing overproduction where marginal social cost exceeds marginal social benefit.
虽然消费者剩余和生产者剩余均增加，但政府的补贴支出超过了剩余增加的总和。多出的部分即为无谓损失，表现为一个三角形，代表边际社会成本大于边际社会收益的过度生产。
Deadweight loss from subsidies arises because resources are allocated to units whose production cost is higher than the willingness of consumers to pay, creating an efficiency loss.
补贴造成无谓损失，是因为资源被配置到生产成本高于消费者支付意愿的产品上，从而造成效率损失。
6. Deadweight Loss from Price Ceilings | 价格上限造成的无谓损失
A price ceiling is a legal maximum price set below the equilibrium price. It creates a shortage because quantity demanded exceeds quantity supplied. The quantity traded falls to the quantity supplied, which is lower than the equilibrium quantity.
价格上限是设在均衡价格之下的法定最高价格，会造成供不应求，因为需求量超过供给量。实际交易量降至供给量，低于均衡数量。
Consumer surplus may increase for those who obtain the good at the lower price, but overall welfare falls. Producer surplus shrinks, and a deadweight loss triangle forms from the mutually beneficial trades that are prevented by the shortage.
对于能以较低价格购买到商品的消费者，消费者剩余可能增加，但总体福利下降。生产者剩余缩小，并且由于短缺阻止了一些互惠互利的交易，形成了无谓损失三角形。
In the case of rent controls, the deadweight loss captures the lost surplus from rental housing that is no longer supplied. The allocation of the scarce units may also lead to additional inefficiencies, such as black markets.
在租金管制情况下，无谓损失反映了不再提供的租赁住房那部分损失的剩余。稀缺单元的分配还可能带来额外低效率，例如黑市。
7. Deadweight Loss from Price Floors | 价格下限造成的无谓损失
A price floor is a legal minimum price set above the equilibrium price. It generates a surplus because quantity supplied exceeds quantity demanded. The quantity traded falls to the quantity demanded, below the equilibrium.
价格下限是设在均衡价格之上的法定最低价格，会导致供给过剩，因为供给量超过需求量。实际交易量降至需求量，低于均衡水平。
Producer surplus may increase for those able to sell, but consumer surplus falls. The deadweight loss triangle captures the lost welfare from the missing trades, as less is consumed than the socially optimal amount.
能够销售的厂商的生产者剩余可能增加，但消费者剩余下降。无谓损失三角形反映了由于交易减少而损失的福利，因为消费量低于社会最优水平。
A typical example is a minimum wage set above the competitive level, which can create unemployment and deadweight loss in labour markets. Similarly, agricultural price supports cause overproduction and waste of resources.
一个典型例子是最低工资设在竞争水平之上，这会在劳动力市场造成失业与无谓损失。同样，农产品价格支持导致生产过剩和资源浪费。
8. Deadweight Loss under Monopoly | 垄断造成的无谓损失
price above marginal cost. This results in a lower output and a higher price than the competitive equilibrium.
垄断者通过边际成本等于边际收益（MR=MC）来最大化利润，并收取高于边际成本的价格。这导致产量低于、价格高于竞争均衡。
Consumer surplus is reduced, and some consumer surplus is transferred to the monopolist as producer surplus (economic profit). However, the reduction in quantity also creates a deadweight loss triangle, representing the net welfare loss to society.
消费者剩余减少，部分消费者剩余被转移给垄断者成为生产者剩余（经济利润）。然而，数量的减少还会形成无谓损失三角形，代表社会福利的净损失。
The deadweight loss under monopoly arises because the monopolist restricts output to raise price, preventing some consumers who value the good more than its marginal cost from buying it.
垄断条件下的无谓损失产生的原因是垄断者限制产量以提高价格，阻止了一些对商品的评价高于其边际成本的消费者购买该商品。
9. Deadweight Loss from Tariffs | 关税造成的无谓损失
An import tariff raises the domestic price above the world price, reducing imports. Domestic production increases (inefficiently) and domestic consumption decreases
Published by TutorHao | A-Level Economics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图