📚 IB Economics Semester Start Test Review | IB经济学期初测试复习梳理
The start of a new semester in IB Economics is the perfect time to revisit core concepts and strengthen your foundation. Whether you are about to sit a diagnostic test or simply want to refresh your knowledge, this revision guide covers the most essential topics from microeconomics and introductory macroeconomics. Each section pairs key explanations in English and Chinese, helping you master terminology and analytical thinking in both languages. Let’s build your confidence for the semester ahead.
新学期的开始是重温IB经济学核心概念、夯实基础的绝佳时机。不论你即将参加摸底测试，还是只想温故知新，本复习指南涵盖微观经济学和宏观经济学导论中最关键的主题。每个小节均以英中双语对照讲解，帮助你同时掌握术语和分析思维，为接下来的学期建立起扎实的信心。
1. Scarcity, Choice, and Opportunity Cost | 稀缺性、选择与机会成本
The fundamental economic problem arises because resources are finite while human wants are unlimited. Scarcity forces individuals, firms, and governments to make choices. Every choice involves an opportunity cost, which is the value of the next best alternative forgone. Understanding this concept is essential for analysing trade-offs in any economic decision.
根本的经济问题源于资源有限而人类欲望无穷。稀缺性迫使个人、企业和政府做出选择。每一次选择都涉及机会成本，即所放弃的次优选项的价值。理解这一概念对于分析任何经济决策中的权衡取舍至关重要。
In IB exams, you need to distinguish between free goods and economic goods. A free good is abundant and has no opportunity cost, such as air, while an economic good is scarce and commands a price. The concept of opportunity cost also underpins the production possibilities curve.
在IB考试中，你需要区分免费物品和经济物品。免费物品丰富且没有机会成本，如空气；而经济物品是稀缺的并且需要价格。机会成本的概念也是生产可能性曲线的基础。
2. The Production Possibilities Curve (PPC) | 生产可能性曲线
The PPC illustrates the maximum combinations of two goods an economy can produce with its existing resources and technology. Points on the curve represent productive efficiency. A movement along the curve shows the opportunity cost of producing more of one good. The curve’s shape, typically concave to the origin, reflects increasing opportunity cost due to imperfect factor substitutability.
PPC展示了一经济体在现有资源和技术下能够生产的两种商品的最大组合。曲线上的点代表生产效率。沿曲线的移动表明了多生产一种商品的机会成本。曲线的形状通常是凹向原点的，这反映了因要素不完全替代而导致的递增机会成本。
An outward shift of the PPC signals economic growth, which can be caused by an increase in the quantity or quality of resources, or by technological progress. Points inside the curve indicate unemployment or inefficiency. This model helps evaluate the trade-offs between capital goods and consumer goods.
PPC的外移表示经济增长，其原因是资源数量或质量的提高，或技术进步。曲线内部的点表明存在失业或低效率。这个模型有助于评估资本品和消费品之间的权衡。
3. Demand | 需求
Demand refers to the quantity of a good or service consumers are willing and able to buy at various prices over a given period. The law of demand states that, ceteris paribus, as the price rises the quantity demanded falls. Price changes cause movements along the demand curve, while non-price determinants such as income, tastes, and the prices of related goods cause the entire curve to shift.
需求是指消费者在一定时期内愿意并且能够以不同价格购买的商品或服务数量。需求定律指出，在其他条件不变的情况下，价格上升则需求量下降。价格变动导致需求量沿需求曲线移动，而收入、偏好和相关商品价格等非价格决定因素则导致整条曲线平移。
A shift to the right represents an increase in demand. Normal goods see demand rise with income, while inferior goods experience the opposite. Substitute goods have a positive cross-price elasticity, and complements have a negative one. Being able to distinguish between a shift and a movement is a vital exam skill.
需求曲线向右平移表示需求增加。正常商品随收入增加需求上升，而低档商品则相反。替代品的交叉价格弹性为正，互补品为负。能够区分曲线平移与顺着曲线移动是一项重要的应试技能。
4. Supply | 供给
Supply is the quantity of a good or service producers are willing and able to offer for sale at different prices during a period. The law of supply states that, ceteris paribus, as the price rises the quantity supplied rises. This positive relationship reflects the profit motive; higher prices provide an incentive to increase output.
供给是指生产者在一定时期内愿意并且能够以不同价格出售的商品或服务的数量。供给定律指出，在其他条件不变的情况下，价格上升则供给量上升。这种正相关关系体现了利润动机；较高的价格激励企业增加产出。
Factors that shift the supply curve include changes in production costs, technology, taxes and subsidies, the number of sellers, and weather conditions for agricultural products. A rightward shift indicates an increase in supply at every price level.
导致供给曲线平移的因素包括生产成本的变化、技术、税收与补贴、卖家的数量以及农产品的天气条件。曲线向右平移表示在每个价格水平上供给量都增加了。
5. Market Equilibrium and Price Mechanism | 市场均衡与价格机制
Market equilibrium occurs where quantity demanded equals quantity supplied. At this price, there is no tendency for change. If the market price is above equilibrium, a surplus pushes the price down; if below, a shortage drives the price up. The invisible hand of the price mechanism rations scarce goods and allocates resources efficiently.
市场均衡发生在需求量等于供给量的地方。在这个价格下，市场没有变化的趋势。如果市场价格高于均衡水平，过剩会迫使价格下降；如果低于均衡水平，短缺会推动价格上涨。价格机制这只“看不见的手”配给稀缺商品，并高效配置资源。
Diagrams showing equilibrium, excess supply, and excess demand are frequently examined. You must be able to explain the adjustment process and illustrate how shifts in demand or supply lead to a new equilibrium price and quantity.
展示均衡、超额供给和超额需求的图形是考试常客。你必须能够解释调整过程，并说明需求或供给的平移如何导致新的均衡价格和数量。
6. Elasticity of Demand and Supply | 需求与供给弹性
Elasticity measures the responsiveness of one variable to a change in another. Price elasticity of demand (PED) captures how sensitive quantity demanded is to a change in the good’s own price. The formula is:
弹性衡量一个变量对另一个变量变化的反应程度。需求的价格弹性 (PED) 反映了需求量对商品自身价格变化的敏感度。公式如下：
PED = %Δ Quantity Demanded ÷ %Δ Price
Demand is elastic when PED > 1, inelastic when PED < 1, and unit elastic when PED = 1. Determinants include the availability of substitutes, the degree of necessity, the proportion of income spent, and time horizon. Firms use PED to judge the impact of price changes on total revenue: raising prices increases total revenue if demand is inelastic.
当 PED > 1 时需求富有弹性，PED < 1 时缺乏弹性，PED = 1 时为单位弹性。决定因素包括替代品的可得性、必需程度、支出占收入的比例以及时间跨度。企业利用 PED 来判断价格变动对总收入的影响：若需求缺乏弹性，提高价格会增加总收入。
Price elasticity of supply (PES) uses a similar formula: %Δ quantity supplied divided by %Δ price. Supply tends to be more elastic in the long run as producers can adjust fixed factors. Cross-price elasticity of demand and income elasticity of demand are also examined in the IB syllabus; they help classify goods as substitutes, complements, normal, or inferior.
供给的价格弹性 (PES) 使用类似的公式：供给量变动的百分比除以价格变动的百分比。供给在长期往往更具弹性，因为生产者可以调整固定要素。需求的交叉价格弹性和收入弹性也是IB考纲内容；它们有助于将商品归类为替代品、互补品、正常品或低档品。
7. Government Intervention: Price Controls and Taxes | 政府干预：价格控制与税收
Governments may intervene in markets to correct perceived inequities or inefficiencies. Price ceilings, such as rent controls, set a maximum legal price. When set below the equilibrium, they create persistent shortages and can encourage black markets. Price floors, like agricultural price supports, set a minimum price and lead to surpluses.
政府可能干预市场以纠正感知到的不公平或低效率。价格上限，如租金管制，规定了法定的最高价格。当上限设定低于均衡水平时，会造成持续短缺并可能助长黑市。价格下限，如农产品价格支持，设定最低价格并导致过剩。
Indirect taxes shift the supply curve vertically upward by the amount of the tax. The tax incidence, or who really bears the burden, depends on the relative elasticities of demand and supply. If demand is inelastic, consumers carry most of the burden. Subsidies shift the supply curve downward and are often used to encourage positive externalities.
间接税会使供给曲线向上垂直平移，平移幅度等于税额。税收归宿，即谁实际承担税负，取决于需求与供给的相对弹性。如果需求缺乏弹性，消费者承担大部分税收负担。补贴会使供给曲线向下平移，通常用于鼓励正外部性。
8. Market Failure and Externalities | 市场失灵与外部性
Market failure occurs when the free market fails to allocate resources efficiently. A key cause is externalities—costs or benefits that affect third parties who are not directly involved in an economic transaction. Negative externalities of production, such as pollution, lead to overproduction because the marginal social cost exceeds the marginal private cost.
市场失灵指自由市场无法有效配置资源的情形。一个关键原因是外部性——影响未直接参与经济交易的第三方的成本或收益。生产的负外部性，如污染，会导致过度生产，因为边际社会成本大于边际私人成本。
Positive externalities, like education or vaccination, lead to underproduction because the marginal social benefit exceeds the marginal private benefit. Governments can use policies such as Pigouvian taxes, subsidies, tradable permits, regulation, and public provision to correct market failures and align private incentives with social welfare.
正外部性，如教育或疫苗接种，会导致生产不足，因为边际社会收益大于边际私人收益。政府可以使用庇古税、补贴、可交易许可证、法规和公共提供等政策来纠正市场失灵，使私人激励与社会福利保持一致。
Other sources of market failure include public goods (non-rival and non-excludable), asymmetric information, and monopoly power. All these topics emphasise the limitations of the price mechanism and the potential role of government.
其他市场失灵的来源包括公共物品（非竞争性和非排他性）、信息不对称以及垄断势力。所有这些主题都强调了价格机制的局限性和政府的潜在作用。
9. Introduction to Macroeconomics: GDP and Economic Growth | 宏观经济学导论：GDP与经济增长
Macroeconomics studies the economy as a whole. Gross Domestic Product (GDP) measures the total market value of all final goods and services produced within a country in a given period. It can be calculated using the expenditure, income, or output approaches. Nominal GDP is valued at current prices, whereas real GDP adjusts for inflation.
宏观经济学研究整体经济。国内生产总值 (GDP) 衡量一国在一定时期内生产的所有最终商品和服务的总市场价值。它可以通过支出法、收入法或产出法计算。名义 GDP 按当期价格计算，而实际 GDP 剔除了通货膨胀的影响。
Economic growth is an increase in the productive potential of the economy, typically measured by the percentage change in real GDP. Sustainable growth raises living standards, but possible drawbacks include environmental damage, increased inequality, and inflation if growth is too rapid.
经济增长是经济体生产潜力的提高，通常用实际 GDP 的百分比变化来衡量。可持续的增长能提高生活水平，但可能带来的弊端包括环境破坏、不平等加剧以及当增长过快时的通货膨胀。
10. Inflation and Unemployment | 通货膨胀与失业
Inflation is a sustained increase in the general price level, most commonly tracked by the Consumer Price Index (CPI). Demand-pull inflation arises when aggregate demand outpaces aggregate supply, while cost-push inflation stems from rising production costs. High and unpredictable inflation erodes purchasing power and creates uncertainty.
通货膨胀是指一般物价水平的持续上升，最常用的衡量指标是消费者价格指数 (CPI)。需求拉动型通货膨胀源于总需求超过总供给，而成本推动型通货膨胀则源于生产成本的上升。高且不可预测的通货膨胀会侵蚀购买力并造成不确定性。
Unemployment measures the number of people actively seeking work but unable to find it, expressed as a percentage of the labour force. Types include cyclical, structural, frictional, and seasonal unemployment. The costs of unemployment are both economic (lost output) and social (increased poverty).
失业衡量的是积极寻找工作但未能找到的人数，以劳动力百分比表示。类型包括周期性、结构性、摩擦性和季节性失业。失业的代价既有经济方面的（产出损失），也有社会方面的（贫困加剧）。
11. Aggregate Demand and Aggregate Supply | 总需求与总供给
Aggregate demand (AD) shows the total spending on domestic goods and services at different price levels. Its components are consumption, investment, government spending, and net exports (C + I + G + (X – M)). The AD curve slopes downward due to the wealth, interest rate, and international trade effects.
总需求 (AD) 显示在不同价格水平下对国内商品和服务的总支出。其组成部分包括消费、投资、政府支出和净出口 (C + I + G + (X – M))。由于财富效应、利率效应和国际贸易效应，AD 曲线向下倾斜。
Aggregate supply (AS) depicts the total output producers are willing to supply. In the short run, the SRAS curve is upward sloping due to sticky wages or input prices. The long-run aggregate supply (LRAS) curve is vertical at the full employment level of output, representing the economy’s potential. Shocks or policy changes can shift both curves, altering the equilibrium price level and real output.
总供给 (AS) 描绘了生产者愿意提供的总产出。在短期内，由于工资或投入品价格粘性，SRAS 曲线向右上方倾斜。长期总供给 (LRAS) 曲线在充分就业产出水平处垂直，代表经济的潜在产出。冲击或政策变化可以平移这两条曲线，改变均衡价格水平和实际产出。
12. Fiscal and Monetary Policy | 财政与货币政策
Fiscal policy involves government manipulation of taxation and spending to influence the economy. Expansionary fiscal policy, such as tax cuts or increased public spending, can boost aggregate demand during a recession. Contractionary policy helps cool an overheating economy. Governments must be aware of the impact on budget deficits and public debt.
财政政策涉及政府通过对税收和支出的操控来影响经济。扩张性财政政策，如减税或增加公共支出，可以在衰退期间刺激总需求。紧缩性政策有助于给过热的经济降温。政府必须意识到对预算赤字和公共债务的影响。
Monetary policy is conducted by a central bank, primarily through changes in interest rates and the money supply. Lower interest rates encourage borrowing and investment, shifting AD to the right. Inflation targeting and open market operations are key tools. The effectiveness of both policies depends on the economic context, time lags, and the state of the global economy.
货币政策由中央银行实施，主要通过调整利率和货币供应量来进行。降低利率鼓励借贷和投资，使 AD 曲线向右平移。通胀目标制和公开市场操作是关键工具。这两种政策的有效性取决于经济背景、时滞以及全球经济的状况。
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