📚 Year 12 AQA Economics: Formula & Key Concept Quick Reference Handbook | Year 12 AQA 经济学：公式与核心概念速查手册
This quick reference handbook is designed for Year 12 students following the AQA Economics specification. It compiles the essential formulas, key concepts, and fundamental relationships you need to master for both microeconomic and macroeconomic analysis. Use it as a checklist for revision and to ensure you can accurately apply these tools in data-response and essay questions.
本速查手册专为学习AQA经济学课程的高一（Year 12）学生设计。手册汇集了微观经济学与宏观经济学分析中必须掌握的核心公式、关键概念与基本关系。你可将其用作复习清单，确保在数据回应题和论文题中准确运用这些工具。
1. Scarcity, Choice, and Opportunity Cost | 稀缺性、选择与机会成本
The fundamental economic problem is scarcity: unlimited wants but finite resources. Every choice involves an opportunity cost, because choosing one option means sacrificing the next best alternative.
基本的经济问题在于稀缺性：无限的欲望与有限的资源。每一个选择都涉及机会成本，因为选择某一选项就意味着放弃次优的可选项。
Opportunity Cost = Value of the next best alternative forgone
机会成本 = 所放弃的次优选择的价值
Opportunity cost includes not only monetary payments but also time, utility, and other non-monetary factors. When evaluating choices, compare the benefits of the selected option with the value of the best alternative sacrificed.
机会成本不仅包括货币支出，还包括时间、效用等非货币因素。在评估选择时，需要将所选选项的收益与所放弃的最佳替代方案的价值进行比较。
2. The Production Possibility Frontier (PPF) | 生产可能性边界
A PPF shows the maximum possible output combinations of two goods given fixed resources and technology. Points on the curve are productively efficient; points inside represent underutilisation of resources. The slope of the PPF is the marginal rate of transformation (MRT), which indicates the opportunity cost of one good in terms of the other.
生产可能性边界展示在资源与技术既定时，两种商品最大可能的产出组合。曲线上的点表示生产有效率；曲线内的点表示资源未充分利用。PPF的斜率即边际转换率（MRT），表示一种商品转换为另一种商品的机会成本。
Opportunity cost of good X = ΔY / ΔX
商品X的机会成本 = ΔY / ΔX
Economic growth, caused by an increase in resources or technological progress, shifts the entire PPF outward. A change in the allocation of resources can move production along the curve, altering the mix of outputs but not the overall capacity.
资源增加或技术进步带来的经济增长会使整个PPF曲线向外移动。资源配置的变化则使生产沿曲线移动，改变产出组合但不会改变总产能。
3. Demand and Supply Functions | 需求与供给函数
The linear demand function is typically written as Qd = a - bP, where a is the quantity demanded when price is zero, and b indicates the responsiveness of quantity demanded to price changes (the gradient of the demand curve). The linear supply function is Qs = c + dP, where c is the quantity supplied when price is zero (often zero or negative), and d reflects the change in quantity supplied for a one-unit change in price.
线性需求函数通常表示为 Qd = a - bP，其中a是价格为零时的需求量，b反映需求量对价格变化的反应程度（需求曲线的斜率）。线性供给函数则为 Qs = c + dP，其中c是价格为零时的供给量（通常为零或负值），d则体现每单位价格变化带来的供给量变化。
Market equilibrium occurs where quantity demanded equals quantity supplied. We set Qd = Qs and solve for the equilibrium price and quantity. This yields the point where the demand and supply curves intersect.
市场均衡发生在需求量与供给量相等时。令 Qd = Qs 并求解即可得到均衡价格与数量，即需求曲线与供给曲线的交点。
4. Price Elasticity of Demand (PED) | 需求的价格弹性
Price elasticity of demand measures the responsiveness of quantity demanded to a change in the good's own price. The formula is:
需求的价格弹性衡量需求量对商品自身价格变化的反应程度。其公式为：
PED = (% Change in Quantity Demanded) / (% Change in Price) = %ΔQd / %ΔP
PED = (需求量变化百分比) / (价格变化百分比) = %ΔQd / %ΔP
y negative because of the law of demand, but the sign is often ignored for interpretation. |PED| > 1 means demand is elastic (sensitive to price changes), |PED| < 1 means demand is inelastic, and |PED| terminants include the availability of substitutes, degree of necessity, proportion of income spent, and time period.
由于需求定律，PED通常为负值，但解释时常忽略负号。|PED| > 1 表示需求富有弹性（对价格变动敏感），|PED| < 1 表示缺乏弹性，|PED| = 1 则为单位弹性。影响因素包括替代品的可得性、必需品程度、支出占收入的比例以及时间长短。
Firms use PED to predict the effect of a price change on total revenue. If demand is elastic, lowering price raises total revenue; if demand is inelastic, raising price increases total revenue.
厂商利用PED预测价格变动对总收益的影响。若需求富有弹性，降低价格会增加总收益；若缺乏弹性，提高价格会增加总收益。
5. Income Elasticity of Demand (YED) and Cross Elasticity of Demand (XED) | 需求的收入弹性与交叉弹性
Income elasticity of demand measures how quantity demanded responds to a change in consumers' income.
需求的收入弹性衡量需求量对消费者收入变化的反应。
YED = (%ΔQd) / (%ΔIncome)
YED = (需求量变化百分比) / (收入变化百分比)
YED > 0 indicates a normal good. Among normal goods, YED > 1 indicates a luxury good (income elastic), whereas 0 < YED < 1 indicates a necessity. YED < 0 indicates an inferior good, where demand falls as income rises.
YED > 0 表示正常品。在正常品中，YED > 1 为奢侈品（富有收入弹性），0 < YED < 1 为必需品。YED < 0 表示低档品，即收入上升时需求下降。
Cross elasticity of demand measures the responsiveness of demand for one good to a change in the price of another good.
需求的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。
XED = (%ΔQd of good A) / (%ΔPrice of good B)
XED = (商品A需求量变化百分比) / (商品B价格变化百分比)
XED > 0 indicates substitute goods (the two goods are consumed in place of each other). XED < 0 indicates complement goods (they are consumed together). XED close to zero suggests the two goods are unrelated.
XED > 0 表示替代品（两种商品可相互替代消费）。XED < 0 表示互补品（两种商品需一起消费）。XED接近于零则表示两种商品不相关。
6. Price Elasticity of Supply (PES) | 供给的价格弹性
Price elasticity of supply measures the responsiveness of quantity supplied to a change in price. The formula is:
供给的价格弹性衡量供给量对价格变化的反应程度。其公式为：
PES = (%ΔQs) / (%ΔP)
PES = (供给量变化百分比) / (价格变化百分比)
ly, and PES = 1 is unit elastic. PES = 0 means perfectly inelastic (fixed supply), while PES = ∞ represents perfectly elastic. Key determinants are the time period, the availability of spare capacity, the ease of storage, and the complexity of the production process.
PES为正值，因为价格上升激励生产者提供更多商品。PES > 1 表示供给富有弹性，PES < 1 表示缺乏弹性，PES = 1 为单位弹性。PES = 0 表示完全无弹性（供给固定），PES = ∞ 则表示完全弹性。主要影响因素包括时间长短、闲置产能、储存难易程度以及生产过程的复杂性。
7. Market Equilibrium and Government Intervention |
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