📚 OCR Economics Year 9 Formula & Theorem Quick Reference | OCR 经济 Year 9 公式定理速查手册
This is your go-to revision sheet for the essential formulas, theorems, and quantitative relationships covered in the Year 9 OCR Economics course. Master these tools to analyse markets, make decisions, and evaluate economic outcomes. Each entry is presented with the English definition immediately followed by its Chinese counterpart, ensuring you are confident in both languages for bilingual exams or study.
这是你复习 Year 9 OCR 经济课程必备公式、定理和量化关系的一站式速查手册。掌握这些工具，你就能分析市场、做出决策并评估经济结果。每个条目都先给出英文定义，紧接着提供中文对照，确保你在双语考试或学习中都能得心应手。
1. The Basic Economic Problem & Opportunity Cost | 基本经济问题与机会成本
ources are scarce but human wants are unlimited. Every choice involves an opportunity cost — lternative forgone. Formula: Opportunity Cost = Value of next best alternative sacrificed.
基本定理：资源是稀缺的，但人的欲望是无限的。每个选择都涉及机会成本——所放弃的次优替代选项。公式：机会成本 = 牺牲的次优替代选项的价值。
If a firm decides to produce 100 units of good A instead of 80 units of good B, the opportunity cost of producing A is the 80 units of B given up. In monetary terms, if the next best use of $1000 was earning 5% interest, the opportunity cost of spending it elsewhere is $50 per year.
如果一家企业决定生产100单位商品A，而不是80单位商品B，那么生产A的机会成本就是放弃的80单位B。货币层面，如果1000美元的最佳替代用途可以获得5%的利息，那么将其花到别处的年机会成本就是50美元。
2. Demand, Supply and Market Equilibrium | 需求、供给与市场均衡
Demand curve: P = a – _s (linear supply). Equilibrium occurs where quantity demanded equals quantity supplied: Qd = Qs, and the equilibrium price is the solution of a – bQ = c + dQ.
需求曲线：P = a – bQ_d（线性需求）。供给曲线：P = c + dQ_s（线性供给）。当需求量等于供给量时达到均衡：Qd = Qs，均衡价格是方程 a – bQ = c + dQ 的解。
The equilibrium quantity Q* = (a – c)/(b + d). Equilibrium price P* = a – ve changes the a parameter; a movement along the curve is caused by a change in own price.
均衡数量 Q* = (a – c)/(b + d)。均衡价格 P* = a – bQ*（或 c + dQ*）。移动与变动：需求曲线的移动会改变参数 a；沿着曲线变动则是由本身价格变化引起。
3. Price Elasticity of Demand (PED) | 需求价格弹性
ED measures the responsiveness of quantity demanded to a change in price. Formula: PED = (% change in quantity demanded) / (% change in price). Using the midpoint method: PED = (ΔQ / Qavg) / (ΔP / Pavg).
PED 衡量需求量对价格变化的反应程度。公式：PED = （需求量变化百分比）/（价格变化百分比）。中点法：PED = (ΔQ / Qavg) / (ΔP / Pavg)。
revenue test: if demand is elastic, a price cut raises total revenue; if inelastic, a price cut lowers total revenue. Total Revenue = Price × Quantity.
如果 PED > 1，需求有弹性（奢侈品、有替代品）。如果 PED < 1，需求无弹性（必需品、成瘾品）。如果 PED = 1，单位弹性。总收入测试：需求有弹性时，降价会增加总收入；需求无弹性时，降价会减少总收入。总收入 = 价格 × 数量。
4. Price Elasticity of Supply (PES) | 供给价格弹性
PES = (% change in quantity supplied) / (% astic supply (difficult to boost output quickly, e.g. agricultural products in short run).
PES = （供给量变化百分比）/（价格变化百分比）。PES > 1：供给有弹性（容易增加产量）。PES < 1：供给无弹性（短期内难以提高产出，如农产品）。
Key determinants: time period (more elastic in the long run), spare production capacity, availability of stocks, and ease of factor substitution. No complex calculation needed at this stage; simply interpret the coefficient.
关键决定因素：时间周期（长期更富弹性）、闲置产能、库存可用性和要素替代的难易程度。现阶段无需复杂计算，只需解读弹性系数。
5. Income Elasticity of Demand (YED) | 需求收入弹性
YED = (% change in quantity demanded) / (% oods have negative YED. Luxury normal goods: YED > 1; necessity normal goods: 0 < YED < 1.
YED = （需求量变化百分比）/（收入变化百分比）。正常品具有正的 YED。低档品具有负的 YED。奢侈性正常品：YED > 1；必需性正常品：0 < YED < 1。
Example: if income rises by 5% and demand for bus travel falls by 2%, YED = -2%/5% D > 1 (e.g. foreign holidays) grow faster than income; during recessions they suffer more.
示例：如果收入上升 5%，公交车出行需求下降 2%，YED = -2%/5% = -0.4，说明公交车出行是低档品。YED > 1 的商品（如出境游）增速快于收入增长；在经济衰退期受到的冲击也更大。
6. Costs, Revenue and Profit | 成本、收益与利润
st (ATC) = TC / Quantity. Average Variable Cost (AVC) = TVC / Quantity. Average Fixed Cost (AFC) = TFC / Quantity. Marginal Cost (MC) = change in TC / change in Quantity.
总固定成本（TFC）：不随产量变化。总可变成本（TVC）：直接随产量变化。总成本（TC）= TFC + TVC。平均总成本（ATC）= TC / 产量。平均可变成本（AVC）= TVC / 产量。平均固定成本（AFC）= TFC / 产量。边际成本（MC）= 总成本变化量 / 产量变化量。
/ Quantity = Price. Marginal Revenue (MR) = change in TR / change in Quantity. Profit = TR – normal profit). Shut-down point (short run): if price < AVC, firm should cease production.
总收入（TR）= 价格 × 销售量。平均收益（AR）= TR / 产量 = 价格。边际收益（MR）= TR 变化量 / 产量变化量。利润 = TR – TC。盈亏平衡点：TR = TC（正常利润）。停止营业点（短期）：如果价格低于 AVC，企业应当停产。
7. Economies and Diseconomies of Scale | 规模经济与规模不经济
Average cost curve is U-shaped because of economies of scale (falling average costs as output expands) and diseconomies of scale (rising average costs beyond an optimal scale). Technical economy formula reminder: higher output spreads fixed costs over more units, so AFC falls.
平均成本曲线呈 U 形，原因在于规模经济（随产量扩大平均成本下降）和规模不经济（超过最优规模后平均成本上升）。技术经济性公式提醒：产出增加让固定成本分摊到更多单位，因此 AFC 下降。
Key sources of economies: purchasing (bulk-buying discounts), managerial (specialisation), financial (lower interest rates for large firms), and technological. Diseconomies: communication breakdown, coordination problems. The minimum efficient scale (MES) is the lowest output at which ATC is minimised.
规模经济的主要来源：采购（批量折扣）、管理（专业化）、融资（大企业利率更低）和技术。规模不经济：沟通不畅、协调困难。最低有效规模（MES）是平均总成本最小化的最低产量。
8. Market Structures – Characteristic Comparisons | 市场结构——特征比较
seller, barriers to entry, price maker, MR < AR (P). Oligopoly: few firms, interdependence, kinked demand curve theory.
没有单一公式，但可以比较定理：完全竞争：众多企业，同质产品，价格接受者，AR = MR = P。垄断：单一卖家，进入壁垒，价格制定者，MR < AR（P）。寡头：少数企业，相互依赖，弯折需求曲线理论。
Concentration ratio (CR): combined market share of the largest n firms (e.g. CR5). A high CR indicates high market power. In Year 9, you only need to identify structures and relate them to efficiency (allocative and productive).
集中度（CR）：最大的 n 家企业市场份额之和（如 CR5）。集中度高表明市场支配力强。Year 9 只需识别市场结构，并将其与效率（配置效率和生产效率）联系起来。
9. Externalities and Social Cost | 外部性与社会成本
it + External Benefit. Negative externality exists when social cost > private cost. Positive externality exists when social benefit > private benefit. The welfare loss (deadweight loss) from a negative externality is the triangle where marginal social cost exceeds marginal private benefit over traded quantity.
社会成本 = 私人成本 + 外部成本。社会收益 = 私人收益 + 外部收益。当社会成本 > 私人成本时存在负外部性。当社会收益 > 私人收益时存在正外部性。负外部性带来的福利损失（无谓损失）是边际社会成本超过边际私人收益的三角形区域，对应于交易量过多。
To internalise an externality, a tax (Pigouvian tax) equal to the marginal external cost at the socially optimal output shifts supply curve upward. Alternatively, a subsidy equal to marginal external benefit can correct a positive externality.
为了将外部性内部化，可以在社会最优产出水平上征收等于边际外部成本的税（庇古税），使供给曲线上移。同样，等于边际外部收益的补贴可以纠正正外部性。
10. Inflation, Unemployment and the Phillips Curve (Intro) | 通胀、失业与菲利普斯曲线（入门）
The short-run Phillips curve suggests an inverse relationship between inflation and unemployment. No precise formula at Year 9, but the trade-off is often expressed as: when unemployment falls below the natural rate, inflation tends to rise. The long-run Phillips curve is vertical at the natural rate of unemployment (NAIRU).
短期菲利普斯曲线表明通胀与失业之间存在反向关系。Year 9 阶段没有精确公式，但权衡关系常表述为：当失业率降至自然率以下时，通胀趋于上升。长期菲利普斯曲线在自然失业率（NAIRU）处垂直。
ket in current year / Cost of basket in base year) × 100. Inflation rate = [(CPI this year – CPI last year) / CPI last year] × 100%.
消费者价格指数（CPI）计算：（当年一篮子商品成本 / 基年一篮子商品成本）× 100。通胀率 = [（今年 CPI – 去年 CPI）/ 去年 CPI] × 100%。
11. Exchange Rates & Balance of Payments Basics | 汇率与国际收支基础
ate index formula: (Current exchange rate / Base year exchange rate) × 100, adjusted for trade weights. For Year 9, simply know that a stronger currency makes exports dearer and imports cheaper.
汇率：以一种货币表示的另一种货币的价格。升值：货币价值上升；贬值：货币价值下降。加权汇率指数公式：（当前汇率 / 基年汇率）× 100，并根据贸易权重调整。Year 9 只需知道本币坚挺会让出口更贵、进口更便宜。
Current account balance ≈ (Exports – site. Simple identity: Current account + Capital account + Financial account = 0 (balancing item).
经常账户余额 ≈ （商品和服务出口 – 进口） + 净海外收入 + 净经常转移。赤字意味着海外支出多于收入；盈余则相反。简单恒等式：经常账户 + 资本账户 + 金融账户 = 0（平衡项目）。
12. Aggregate Demand & Aggregate Supply Framework | 总需求与总供给框架
AD = C + I + G + (X – s downward due to the wealth effect, interest-rate effect, and international trade effect.
AD = C + I + G + (X – M)。C = 消费，I = 投资，G = 政府支出，X = 出口，M = 进口。总需求曲线向右下倾斜，原因包括财富效应、利率效应和国际贸易效应。
vertical, determined by factor endowments, technology, and institutional quality. Macroeconomic equilibrium: AD = SRAS.
短期总供给（SRAS）向右上倾斜，原因包括工资黏性、菜单成本或感知偏差。长期总供给（LRAS）垂直，由要素禀赋、技术和制度质量决定。宏观经济均衡：AD = SRAS。
Applying this handbook will sharpen your economic reasoning. Always link formulas back to real-world examples—that’s how OCR examiners want you to show application and analysis.
运用这本手册将提升你的经济学推理能力。始终将公式与现实例子相联系——这正是 OCR 考官期待你展现的应用与分析能力。
Published by TutorHao | Economics Revision Series | aleveler.com
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