📚 AS CCEA Economics: Essential Formulas and Theorems Quick Reference | AS CCEA 经济：公式定理速查手册
This handbook brings together the key formulas, definitions and graphical theorems that every AS CCEA Economics student must master. Each concept is stated clearly, with its quantitative expression explained in both English and Chinese, helping you build fluency for multiple‑choice questions, data‑response tasks and structured essays.
这本手册汇集了每一位 AS CCEA 经济学生都必须掌握的核心公式、定义和图形定理。每个概念都清晰陈述，并用中英文解释其量化表达，帮助你在选择题、数据分析题和结构化论文中熟练运用。
1. Price Elasticity of Demand (PED) | 需求价格弹性
PED measures how responsive the quantity demanded of a good is to a change in its price. It is calculated as the percentage change in quantity demanded divided by the percentage change in price.
需求价格弹性衡量商品需求量对其价格变化的反应程度，计算公式为需求量变动的百分比除以价格变动的百分比。
PED = %ΔQd ÷ %ΔP
Numerical values range from perfectly inelastic (PED = 0) through unit elastic (PED = 1) to perfectly elastic (PED = ∞). An absolute value greater than 1 indicates elastic demand; less than 1 indicates inelastic demand.
数值范围从完全无弹性(PED=0)到单位弹性(PED=1)再到完全弹性(PED=∞)。绝对值大于1表示需求富有弹性，小于1表示需求缺乏弹性。
Total revenue (TR = P × Q) changes predictably with elasticity: if demand is elastic, a price rise lowers TR; if inelastic, a price rise raises TR.
总收益(TR=P×Q)随弹性变化可预测：若需求富有弹性，提价会使总收益减少；若缺乏弹性，提价会使总收益增加。
The midpoint formula avoids different results depending on the direction of change. PED = (ΔQ / ((Q₁+Q₂)/2)) ÷ (ΔP / ((P₁+P₂)/2)).
中点公式避免了因变化方向不同而产生不同结果。PED=(ΔQ/((Q₁+Q₂)/2))÷(ΔP/((P₁+P₂)/2))。
2. Income Elasticity of Demand (YED) | 需求收入弹性
YED quantifies the sensitivity of demand to a change in consumer income. It is found by dividing the percentage change in quantity demanded by the percentage change in income.
需求收入弹性量化需求对消费者收入变化的敏感度，由需求量变动百分比除以收入变动百分比得到。
YED = %ΔQd ÷ %ΔY
A positive YED identifies a normal good; if YED > 1 the good is a luxury. A negative YED identifies an inferior good.
正的YED表示正常商品；若YED>1则为奢侈品。负的YED表示低档商品。
Firms use YED to forecast how sales will shift during economic growth or recession, guiding output and marketing decisions.
企业利用YED预测经济扩张或衰退时销售的变化，从而指导产量与营销决策。
3. Cross Elasticity of Demand (XED) | 需求交叉弹性
XED measures the responsiveness of demand for one good when the price of another good changes. It is the percentage change in quantity demanded of good A divided by the percentage change in price of good B.
需求交叉弹性衡量一种商品的需求对另一种商品价格变化的反应程度，等于商品A需求量变动百分比除以商品B价格变动百分比。
XED = %ΔQdA ÷ %ΔPB
Positive XED signals substitute goods; negative XED signals complements. A value close to zero suggests independent goods.
正的XED表明替代品；负的XED表明互补品。数值接近零意味着商品相互独立。
Policymakers and firms use XED to assess the degree of competition and to predict the impact of a rival’s pricing strategy.
政策制定者和企业利用XED评估竞争程度，并预测对手定价策略的影响。
4. Price Elasticity of Supply (PES) | 供给价格弹性
PES captures the responsiveness of quantity supplied to a change in price. It is calculated as the percentage change in quantity supplied divided by the percentage change in price.
供给价格弹性反映供给量对价格变化的反应程度，等于供给量变动百分比除以价格变动百分比。
PES = %ΔQs ÷ %ΔP
PES depends mainly on the time period and the availability of spare capacity. In the momentary period supply is often perfectly inelastic; in the long run it becomes more elastic.
PES主要取决于时间跨度和闲置产能的可得性。在瞬时供给常常完全无弹性；在长期则变得更有弹性。
A value > 1 shows elastic supply; < 1 shows inelastic supply. Agricultural goods frequently exhibit inelastic supply in the short run.
数值大于1表示供给富有弹性，小于1表示缺乏弹性。农产品在短期经常表现为供给缺乏弹性。
5. Consumer and Producer Surplus | 消费者剩余与生产者剩余
Consumer surplus is the difference between what consumers are willing to pay and what they actually pay. On a demand‑supply diagram it is the area below the demand curve and above the equilibrium price.
消费者剩余是消费者愿意支付的价格与实际支付的价格之差。在供求图中，它是需求曲线下方、均衡价格上方的面积。
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 equilibrium price.
生产者剩余是生产者获得的价格与它们愿意接受的最低价格之差，即供给曲线上方、均衡价格下方的面积。
Consumer Surplus = ½ × (Pmax − Pe) × Qe
Producer Surplus = ½ × (Pe − Pmin) × Qe
Total welfare is the sum of consumer and producer surplus. Any market intervention that reduces this total creates a deadweight loss.
总福利是消费者剩余与生产者剩余之和。任何减少此总值的市场干预都会造成无谓损失。
6. Indirect Taxes and Their Welfare Effects | 间接税及其福利效应
An indirect tax (ad valorem or specific) shifts the supply curve vertically upwards by the amount of the tax. The new equilibrium price (Pc) is paid by consumers, while producers receive Pp = Pc − tax.
间接税（从价税或从量税）使供给曲线向上垂直移动税额幅度。新的均衡价格(Pc)由消费者支付，而生产者得到 Pp=Pc−税额。
Tax burden on consumers = (Pc − Pe) × Qtax
Tax burden on producers = (Pe − Pp) × Qtax
The division of the tax burden depends on the relative elasticities of demand and supply. The more inelastic side bears a larger share.
税收负担的分割取决于需求与供给的相对弹性。越缺乏弹性的一方承担更大的份额。
A deadweight loss triangle appears between the original and new equilibrium quantities, representing trades that no longer occur.
在原均衡数量与新均衡数量之间出现一个无谓损失三角形，代表不再发生的交易。
7. Subsidies and Their Impact | 补贴及其影响
A subsidy lowers the cost of production and shifts the supply curve vertically downwards. The new consumer price falls, the quantity traded increases, and producers receive Pp = Pc + subsidy per unit.
补贴降低了生产成本，使供给曲线垂直向下移动。消费者价格下降，交易量增加，生产者获得 Pp=Pc+单位补贴。
Producer gain = (Pp − Pe) × Qsub
Consumer gain = (Pe − Pc) × Qsub
The total cost to the government equals the subsidy per unit multiplied by the new quantity. Part of this spending becomes deadweight loss because the marginal social benefit of the extra units is less than their marginal social cost.
政府总成本等于单位补贴乘以新的数量。部分支出成为无谓损失，因为额外单位的社会边际收益低于其社会边际成本。
8. Price Controls: Maximum and Minimum Prices | 价格管制：最高限价与最低限价
A maximum price set below the equilibrium creates excess demand (shortage), while a minimum price set above the equilibrium creates excess supply (surplus).
最高限价设定在均衡价格以下会导致超额需求（短缺），最低限价设定在均衡价格以上则导致超额供给（过剩）。
With a binding maximum price, the quantity traded falls to the quantity supplied, generating a welfare loss. Informal markets may emerge.
在有效的最高限价下，交易量下降至供给量，产生福利损失，并可能出现非正式市场。
A minimum price (e.g. agricultural price floor) leads to government or producer intervention to purchase the surplus, incurring additional costs.
最低限价（如农产品保护价）导致政府或生产者必须购买过剩部分，带来额外成本。
Both policies prevent the market from reaching allocative efficiency, and deadweight loss can be identified on the standard diagram.
两种政策都阻碍了市场达到配置效率，无谓损失可在标准图中识别。
9. Costs, Revenues and Profit Maximisation | 成本、收益与利润最大化
Short‑run costs are divided into fixed costs (FC) and variable costs (VC). Total cost TC = FC + VC. Average cost AC = TC ÷ Q. Marginal cost MC = ΔTC ÷ ΔQ.
短期成本分为固定成本(FC)和可变成本(VC)。总成本TC=FC+VC。平均成本AC=TC÷Q。边际成本MC=ΔTC÷ΔQ。
MC = ΔTC ÷ ΔQ, AC = TC ÷ Q, AVC = VC ÷ Q
On the revenue side, total revenue TR = P × Q. Average revenue AR = TR ÷ Q = Price. Marginal revenue MR = ΔTR ÷ ΔQ.
在收益方面，总收入TR=P×Q。平均收益AR=TR÷Q=价格。边际收益MR=ΔTR÷ΔQ。
The profit‑maximising rule in all market structures is to produce where MR = MC, provided that price exceeds average variable cost in the short run.
所有市场结构中利润最大化的规则是生产达到MR=MC的产量，前提是在短期价格高于平均可变成本。
At the output where MR=MC, any deviation would reduce total profit; this condition is fundamental to understanding firm behaviour.
在MR=MC的产量水平上，任何偏离都会减少总利润；这一条件对理解企业行为至关重要。
10. Perfect Competition and Monopoly | 完全竞争与垄断
In perfect competition, firms are price‑takers facing a horizontal demand curve at the market price. Thus AR = MR = Price. The short‑run equilibrium occurs where P = MC, and supernormal profits may exist.
在完全竞争中，企业是价格接受者，面临一条在市场定价水平的水平需求曲线。因此AR=MR=价格。短期均衡位于P=MC处，并可能存在超额利润。
In monopoly, the firm faces a downward‑sloping demand curve. AR = demand, but MR lies below AR. The monopolist maximises profit at MR = MC and then charges the price read off the demand curve.
在垄断中，企业面临向下倾斜的需求曲线。AR=需求，但MR位于AR下方。垄断者在MR=MC处产量最大化利润，然后根据需求曲线定价。
Monopoly can lead to higher prices and lower output than perfect competition, causing a deadweight loss. However, economies of scale may offset some inefficiency.
垄断可能导致比完全竞争更高的价格和更低的产量，造成无谓损失。但规模经济可能抵消部分低效率。
Comparing the two structures highlights the role of barriers to entry: high barriers protect monopoly power, while free entry drives perfect competition towards normal profit.
比较两种结构突出进入壁垒的作用：高壁垒保护垄断势力，而自由进入使得完全竞争趋向正常利润。
11. Macroeconomic Indicators | 宏观经济指标
The inflation rate is usually measured by the Consumer Price Index (CPI). CPI = (cost of fixed basket in current year ÷ cost of fixed basket in base year) × 100.
通货膨胀率通常以消费者物价指数(CPI)衡量。CPI=(固定篮子现年成本÷固定篮子基年成本)×100。
Inflation rate = (CPIt − CPIt−1) ÷ CPIt−1 × 100
The unemployment rate is the proportion of the labour force that is out of work and actively seeking employment.
失业率是劳动力中失业并积极寻找工作的人口比例。
Unemployment rate = (Number unemployed ÷ Labour force) × 100
Real GDP is nominal GDP adjusted for inflation, using the GDP deflator: Real GDP = (Nominal GDP ÷ GDP deflator) × 100. The GDP deflator itself is a broad measure of the price level.
实际GDP是经通胀调整的名义GDP，使用GDP平减指数：实际GDP=(名义GDP÷GDP平减指数)×100。GDP平减指数本身是价格水平的广泛量度。
12. The Multiplier Effect | 乘数效应
The multiplier shows the magnified impact of an initial injection of spending on national income. Its size depends on the marginal propensity to consume (MPC) and the marginal propensity to save (MPS), where MPC + MPS = 1.
乘数显示最初一笔支出对国民收入的放大效应。其大小取决于边际消费倾向(MPC)和边际储蓄倾向(MPS)，且MPC+MPS=1。
Multiplier k = 1 ÷ MPS = 1 ÷ (1 − MPC)
An increase in investment ΔI raises GDP by ΔY = k × ΔI. The process continues through successive rounds of spending, each smaller than the last.
投资增加ΔI使得GDP增加ΔY=k×ΔI。这个过程通过一轮轮递减的支出继续下去。
The multiplier can work in reverse: a withdrawal of spending contracts national income by more than the initial withdrawal. Understanding the multiplier enables governments to design effective fiscal policies.
乘数也可反向作用：撤回一笔支出会使国民收入收缩幅度超过最初撤回额。理解乘数有助于政府设计有效的财政政策。
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