📚 Microeconomics Core Concepts Review | 微观经济学核心知识点梳理
Microeconomics examines the behaviour of individual economic agents – households and firms – and how their interactions in markets determine the allocation of scarce resources. This revision guide covers the essential concepts, from opportunity cost to market failure, providing a structured overview for A‑Level Economics candidates. Understanding these fundamentals is crucial for analysing real‑world issues and succeeding in examinations.
微观经济学研究个体经济主体——家庭和厂商——的行为，以及它们在市场中的相互作用如何决定稀缺资源的配置。这篇复习指南涵盖了从机会成本到市场失灵的核心概念，为 A‑Level 经济学考生提供了一个系统性的知识梳理。掌握这些基本原理对分析现实世界问题和在考试中取得成功至关重要。
1. Scarcity and Opportunity Cost | 稀缺性与机会成本
Economics begins with the fundamental problem of scarcity: resources such as land, labour, capital, and entrepreneurship are limited, yet human wants are virtually unlimited. This mismatch forces individuals, firms, and governments to make choices. Every choice involves a trade‑off, and the value of the next best alternative forgone is the opportunity cost.
经济学从稀缺性这一根本问题开始：土地、劳动、资本和企业家才能等资源是有限的，而人类的欲望几乎是无限的。这种不匹配迫使个人、企业和政府做出选择。每一个选择都涉及权衡，而所放弃的次优替代方案的价值就是机会成本。
The production possibility frontier (PPF) illustrates scarcity, choice, and opportunity cost graphically. Points on the curve represent efficient output combinations; points inside are inefficient, and points outside are unattainable with current resources. An outward shift of the PPF indicates economic growth.
生产可能性边界（PPF）用图形展示了稀缺性、选择和机会成本。曲线上的点代表有效率的产出组合；曲线内的点表示效率低下，曲线外的点则用现有资源无法达到。PPF 向外移动表示经济增长。
The four factors of production are:
- Land – all natural resources / 土地 – 所有自然资源
- Labour – human effort / 劳动 – 人类努力
- Capital – man‑made aids for production / 资本 – 用于生产的人造辅助物
- Entrepreneurship – the willingness to take risks and innovate / 企业家精神 – 承担风险和创新的意愿
2. Demand and the Law of Demand | 需求与需求定律
Demand refers to the quantity of a good or service that consumers are willing and able to buy at various prices over a given period, ceteris paribus. The law of demand states that, all else being equal, as the price of a good rises, the quantity demanded falls, and vice versa. This inverse relationship reflects the income effect and the substitution effect.
需求是指在给定时期内，在其他条件不变的情况下，消费者愿意并且能够以各种价格购买的某种商品或服务的数量。需求定律指出，其他条件不变时，商品价格上升，需求量下降，反之亦然。这种反向关系反映了收入效应和替代效应。
A movement along the demand curve is caused solely by a change in the good’s own price. A shift of the demand curve, on the other hand, results from changes in non‑price determinants such as income, tastes, prices of related goods (substitutes and complements), expectations, and the number of buyers.
沿着需求曲线的移动仅由商品自身价格变化引起。而需求曲线的平移则源于非价格决定因素的变化，例如收入、偏好、相关商品（替代品和互补品）的价格、预期以及买者数量。
The demand function can be written as:
Qd = f(P, Y, Ps, Pc, T, E, N)
where P = own price, Y = income, Ps = price of substitutes, Pc = price of complements, T = tastes, E = expectations, and N = number of consumers.
其中 P = 自身价格，Y = 收入，Ps = 替代品价格，Pc = 互补品价格，T = 偏好，E = 预期，N = 消费者数量。
3. Supply and the Law of Supply | 供给与供给定律
Supply is the quantity of a good that producers are willing and able to offer for sale at various prices over a period. The law of supply states that, ceteris paribus, a higher price leads to a greater quantity supplied, as higher prices increase the potential profit and incentive to produce.
供给是指在一定时期内，生产者愿意并且能够以各种价格提供出售的商品数量。供给定律指出，在其他条件不变的情况下，价格越高，供给量越大，因为更高的价格增加了潜在利润和生产激励。
As with demand, a change in own price causes a movement along the supply curve, whereas shifts of the curve are triggered by factors such as input costs, technology, taxes and subsidies, prices of related goods in production, expectations, and the number of sellers.
与需求类似，自身价格变化引起沿着供给曲线的移动，而曲线平移则是由投入成本、技术、税收和补贴、生产中的相关商品价格、预期以及卖者数量等因素触发的。
The basic supply function is:
Qs = f(P, Ci, Tech, Tax, Subs, Pprod, E, N)
where Ci = cost of inputs, Tech = technology, Tax = indirect taxes, Subs = subsidies, Pprod = prices of related goods in production.
其中 Ci = 投入成本，Tech = 技术，Tax = 间接税，Subs = 补贴，Pprod = 生产中相关商品的价格。
4. Market Equilibrium | 市场均衡
Market equilibrium occurs where the quantity demanded equals the quantity supplied at a given price. This equilibrium price (Pe) and quantity (Qe) represent a state of rest, with no inherent tendency to change unless an external shock shifts demand or supply. Graphically, it is the intersection of the demand and supply curves.
市场均衡发生在给定价格下需求量等于供给量时。这一均衡价格（Pe）和均衡数量（Qe）代表一种静止状态，除非外部冲击使需求或供给平移，否则没有内在的变化倾向。在图形中，它是需求曲线和供给曲线的交点。
When the market price is above equilibrium, excess supply (a surplus) arises, putting downward pressure on price. When price is below equilibrium, excess demand (a shortage) pushes price upward. The price mechanism thus allocates resources without central direction.
当市场价格高于均衡时，出现超额供给（过剩），对价格产生下行压力。当价格低于均衡时，超额需求（短缺）推动价格上升。因此，价格机制无需中央指导即可配置资源。
The functions of the price mechanism include signalling, rationing, and providing incentives. For example, a higher price signals producers to increase output and rations scarce goods to those most willing to pay.
价格机制的功能包括信号传递、配给和提供激励。例如，较高的价格向生产者发出增加产出的信号，并配给稀缺商品给最愿意支付的人。
5. Price Elasticity of Demand | 需求价格弹性
Price elasticity of demand (PED) measures the responsiveness of quantity demanded to a change in price. It is calculated as:
PED = % change in Qd / % change in P
需求价格弹性（PED）衡量需求量对价格变化的反应程度。计算公式为：
PED = Qd 变动的百分比 / P 变动的百分比
If the absolute value of PED is greater than 1, demand is price elastic; if less than 1, it is price inelastic; if equal to 1, unit elastic; perfectly elastic gives PED = ∞, and perfectly inelastic gives PED = 0. The key determinants include the availability of substitutes, the degree of necessity, the proportion of income spent, and time period.
如果 PED 的绝对值大于 1，需求是富有弹性的；小于 1，缺乏弹性；等于 1，为单位弹性；完全弹性时 PED = ∞，完全无弹性时 PED = 0。关键决定因素包括替代品的可获得性、必需程度、支出占收入的比例以及时间长短。
Total revenue (TR) and PED are closely related. When demand is elastic, a price rise reduces TR; when inelastic, a price rise increases TR. This relationship guides firms’ pricing strategies and government tax policy.
总收入（TR）和 PED 密切相关。当需求富有弹性时，提价会降低总收入；当需求缺乏弹性时，提价会增加总收入。这一关系指导着企业的定价策略和政府的税收政策。
6. Other Elasticities | 其他弹性
Income elasticity of demand (YED) measures the responsiveness of demand to changes in income:
YED = % change in Qd / % change in income
Normal goods have positive YED; luxury goods have YED > 1; necessities have YED between 0 and 1. Inferior goods have negative YED.
需求收入弹性（YED）衡量需求对收入变化的反应程度。正常商品具有正的 YED；奢侈品 YED > 1；必需品 YED 介于 0 和 1 之间。低档商品具有负的 YED。
Cross elasticity of demand (XED) measures the responsiveness of demand for good A to a change in price of good B:
XED = % change in Qd of A / % change in P of B
Substitutes have positive XED; complements have negative XED. Unrelated goods have XED close to zero.
需求交叉弹性（XED）衡量 A 商品的需求对 B 商品价格变化的反应程度。替代品具有正的 XED；互补品具有负的 XED。不相关商品的 XED 接近于零。
Price elasticity of supply (PES) measures the responsiveness of quantity supplied to a change in price:
PES = % change in Qs / % change in P
It depends mainly on production time lags, spare capacity, and the ability to store output. PES tends to be more elastic in the long run.
供给价格弹性（PES）衡量供给量对价格变化的反应程度。它主要取决于生产时滞、闲置产能和存储产出的能力。在长期中 PES 往往更有弹性。
7. Consumer and Producer Surplus | 消费者与生产者剩余
Consumer surplus is the difference between what consumers are willing to pay for a good and what they actually pay. It is the area below the demand curve and above the market price. Producer surplus is the difference between the price producers receive and the minimum price they are willing to accept; it is the area above the supply curve and below the market price.
消费者剩余是消费者愿意为一种商品支付的最高金额与他们实际支付金额之间的差额。它是需求曲线下方、市场价格上方的面积。生产者剩余是生产者实际收到的价格与他们愿意接受的最低价格之间的差额；它是供给曲线上方、市场价格下方的面积。
Total welfare in a free market is the sum of consumer and producer surplus. Any government intervention, such as price controls or taxes, can reduce this total welfare, creating a deadweight loss (DWL). The deadweight loss represents a loss of economic efficiency.
自由市场上的总福利是消费者剩余与生产者剩余之和。任何政府干预，如价格控制或税收，都可能减少这一总福利，造成无谓损失（DWL）。无谓损失代表着经济效率的损失。
8. Government Intervention: Price Controls | 政府干预：价格控制
Governments sometimes intervene in markets by setting price ceilings or price floors. A price ceiling is a maximum legal price set below the equilibrium, often applied to essential goods like rent or staple foods. It leads to a persistent shortage because quantity demanded exceeds quantity supplied at the capped price.
政府有时通过设定价格上限或下限来干预市场。价格上限是设定在均衡水平以下的一个法定最高价格，通常用于租金或主食等生活必需品。它会导致持续性短缺，因为在限价水平上需求量超过供给量。
A price floor is a minimum legal price set above the equilibrium, commonly seen in agricultural price supports or minimum wage legislation. It creates excess supply (a surplus), as producers are willing to supply more than consumers purchase at the higher price. In the case of a minimum wage, this can lead to unemployment.
价格下限是设定在均衡水平以上的一个法定最低价格，常见于农产品价格支持或最低工资立法。它会造成超额供给（过剩），因为生产者在较高的价格下愿意供给的数量超过消费者购买的数量。就最低工资而言，这可能导致失业。
Both price ceilings and floors generate deadweight loss, encourage black markets, and may have unintended consequences for equity and efficiency.
价格上限和下限都会产生无谓损失，鼓励黑市，并可能对公平和效率带来意想不到的后果。
9. Government Intervention: Taxes and Subsidies | 政府干预：税收与补贴
Indirect taxes, such as excise duties or value‑added tax (VAT), can be specific (a fixed amount per unit) or ad valorem (a percentage of the price). Imposing an indirect tax shifts the supply curve vertically upward by the amount of the tax, raising the price for consumers and reducing the price received by suppliers. The tax burden is shared between consumers and producers depending on the relative elasticities of demand and supply.
间接税，如消费税或增值税（VAT），可以是从量税（每单位固定金额）或从价税（价格的百分比）。征收间接税会使供给曲线垂直向上移动税额的量，提高消费者支付的价格，同时降低供应商收到的价格。税收负担由消费者和生产者根据需求和供给的相对弹性分担。
Subsidies are payments from the government to producers, effectively lowering their costs. They shift the supply curve downward, reducing the market price and increasing equilibrium quantity. While subsidies benefit consumers and encourage production, they also impose a cost on taxpayers and can lead to overproduction.
补贴是政府向生产者支付的款项，实际上降低了他们的成本。补贴使供给曲线向下移动，降低市场价格，增加均衡数量。虽然补贴使消费者受益并鼓励生产，但它们也给纳税人带来成本，并可能导致生产过剩。
The welfare effects include a deadweight loss triangle because the marginal social cost of the subsidised output exceeds the marginal social benefit beyond the free‑market equilibrium.
福利效应包括一个无谓损失三角形，因为补贴产出在超过自由市场均衡后，边际社会成本超过了边际社会效益。
10. Market Structures | 市场结构
Market structures range from perfect competition to pure monopoly. In perfect competition, there are many small firms producing identical products, with no barriers to entry or exit. Firms are price takers, and in the long run only normal profits are made. Efficiency is achieved in both productive and allocative senses.
市场结构从完全竞争到完全垄断不等。在完全竞争中，有许多小厂商生产同质产品，没有进入或退出的壁垒。厂商是价格接受者，长期中只能获得正常利润。在生产效率和配置效率两方面都得以实现。
Monopoly exists when a single firm dominates the market, facing a downward‑sloping demand curve and high barriers to entry. A monopolist can earn supernormal profits in the long run but generally produces a lower quantity and charges a higher price than would occur under perfect competition, leading to allocative inefficiency.
当一家企业主宰市场，面临向下倾斜的需求曲线和高进入壁垒时，就形成了垄断。垄断者可以在长期中获得超额利润，但通常比完全竞争下生产的数量更少、要价更高，导致配置效率损失。
Imperfect competition includes monopolistic competition, where many firms sell differentiated products, and oligopoly, where a few interdependent firms dominate. Oligopolistic markets often feature strategic behaviour, price rigidity, non‑price competition, and the possibility of collusion.
不完全竞争包括垄断竞争（许多企业销售差异化产品）和寡头垄断（少数相互依存的企业主导市场）。寡头市场通常具有策略性行为、价格刚性、非价格竞争以及合谋的可能性等特征。
Concentration ratios and the Herfindahl‑Hirschman Index (HHI) are commonly used to measure market power.
集中度比率和赫芬达尔‑赫希曼指数（HHI）常用于衡量市场势力。
11. Market Failure and Externalities | 市场失灵与外部性
Market failure occurs when the free market fails to allocate resources efficiently, resulting in a net loss of social welfare. A primary cause is the presence of externalities – costs or benefits imposed on third parties not directly involved in a transaction. Negative production externalities, such as pollution, lead to over‑production because private costs are lower than social costs.
当自由市场无法有效配置资源，导致社会净福利损失时，就发生了市场失灵。一个主要原因是外部性的存在——强加于未直接参与交易的第三方身上的成本或收益。负生产外部性，如污染，会导致过度生产，因为私人成本低于社会成本。
Positive consumption externalities, like vaccinations, lead to under‑consumption because private benefits are smaller than social benefits. Governments may correct these inefficiencies through taxation (Pigouvian taxes), subsidies, regulation, tradable permits, or direct provision.
正消费外部性，如疫苗接种，会导致消费不足，因为私人收益小于社会收益。政府可以通过税收（庇古税）、补贴、监管、可交易许可证或直接提供来纠正这些低效率。
The socially optimal level of output occurs where marginal social cost (MSC) equals marginal social benefit (MSB). Externalities cause a divergence between private and social valuations.
社会最优产出水平出现在边际社会成本（MSC）等于边际社会收益（MSB）之时。外部性导致了私人估值与社会估值之间的偏离。
12. Public Goods and Information Asymmetry | 公共品与信息不对称
Public goods are both non‑rivalrous and non‑excludable, which means the free market will not provide them in sufficient quantities because of the free‑rider problem. Examples include national defence, street lighting, and clean air. Such goods require government provision funded by taxation.
公共品同时具有非竞争性和非排他性，这意味着由于搭便车问题，自由市场不会提供足够数量。例子包括国防、路灯和清洁空气。这些物品需要由政府通过税收资助来提供。
Information failure arises when consumers or producers lack full knowledge of the benefits or costs of a product, leading to market failure. Asymmetric information leads to adverse selection and moral hazard. For instance, sellers may know more about a used car than buyers (lemons problem), or insured individuals may take greater risks.
当消费者或生产者对产品的收益或成本缺乏充分了解时，就会出现信息失灵，导致市场失灵。信息不对称会导致逆向选择和道德风险。例如，卖方可能比买方更了解二手车（柠檬问题），或者被保险人可能承担更大风险。
Market failure can also be caused by factor immobility, monopoly power, and short‑termism. A combination of policies is often needed to improve social welfare outcomes.
市场失灵也可能由要素不可流动性、垄断势力和短期主义引起。通常需要组合政策来改善社会福利结果。
Published by TutorHao | Economics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导