📚 SQA Year 10 Economics: Formula & Theorem Quick Reference Handbook | SQA 十年级经济：公式定理速查手册
Welcome to your fast-track revision companion for SQA National 5 Economics. This handbook brings together all the key formulas, definitions and cause-and-effect relationships you need to analyse markets, measure economic performance and understand government policy. Use it to test yourself, to tackle data-response questions and to build the confidence that comes from knowing your toolkit inside out.
欢迎使用 SQA 国家五级经济快速复习手册。本手册汇总了你需要掌握的所有核心公式、定义和因果关系，帮助你分析市场、衡量经济表现并理解政府政策。用它来自我检测、攻克数据题，并在彻底掌握工具包的过程中建立信心。
1. Price Elasticity of Demand (PED) | 需求价格弹性
Price elasticity of demand measures how responsive the quantity demanded of a good is to a change in its price. It is always a negative number, but we often ignore the minus sign and focus on the absolute value.
需求价格弹性衡量一种商品的需求量对其自身价格变化的反应程度。它总是负数，但我们通常忽略负号，只看绝对值。
PED = % Change in Quantity Demanded ÷ % Change in Price
d has unitary elasticity. A perfectly inelastic demand curve is vertical (PED = 0), and a perfectly elastic demand curve is horizontal (PED = ∞).
如果 PED > 1，需求富有弹性：需求量对价格变化的反应程度大于价格变化本身的比例。如果 PED < 1，需求缺乏弹性。如果 PED = 1，需求是单位弹性。完全无弹性的需求曲线是垂直的（PED = 0），完全有弹性的需求曲线是水平的（PED = ∞）。
Determinants include the number of close substitutes, the proportion of income spent on the good, whether it is a necessity or a luxury, and the time period considered.
影响因素包括相近替代品的数量、该商品占收入的比例、它是必需品还是奢侈品，以及所考虑的时间范围。
2. Income Elasticity of Demand (YED) | 需求收入弹性
Income elasticity of demand shows how quantity demanded changes in response to a change in consumers' income. The sign tells us whether the good is normal or inferior, while the size indicates whether it is a luxury or a necessity.
需求收入弹性显示需求量如何随消费者收入的变化而变化。符号说明商品是正常品还是劣等品，数值大小表明它是奢侈品还是必需品。
YED = % Change in Quantity Demanded ÷ % Change in Income
A positive YED means the good is normal. For normal necessities, 0 < YED < 1; for normal luxuries, YED > 1. A negative YED indicates an inferior good: as income rises, demand falls. Firms use YED to forecast sales and plan output across different phases of the business cycle.
正的 YED 表示商品是正常品。正常必需品：0 < YED < 1；正常奢侈品：YED > 1。负的 YED 表示商品是劣等品：收入增加时需求下降。企业利用 YED 预测销售，并在经济周期的不同阶段规划产出。
3. Cross Elasticity of Demand (XED) | 需求交叉弹性
Cross elasticity of demand examines how the quantity demanded of one good (A) changes when the price of another good (B) changes. The sign reveals whether the two goods are substitutes or complements.
需求交叉弹性考察一种商品（A）的需求量如何随着另一种商品（B）价格的变化而变化。其符号揭示两种商品是替代品还是互补品。
XED = % Change in Quantity Demanded of Good A ÷ % Change in Price of Good B
If XED > 0, the goods are substitutes (e.g. tea and coffee). A rise in the price of B increases demand for A. If XED < 0, they are complements (e.g. printers and ink cartridges). The closer XED is to zero, the weaker the relationship between the two products.
如果 XED > 0，它们是替代品（如茶和咖啡）。B 的价格上涨会增加对 A 的需求。如果 XED < 0，它们是互补品（如打印机和墨盒）。XED 越接近零，两种产品之间的关系越弱。
4. Price Elasticity of Supply (PES) | 供给价格弹性
Price elasticity of supply measures the responsiveness of quantity supplied to a change in price. It is usually positive because higher prices give producers an incentive to supply more.
供给价格弹性衡量供给量对价格变化的反应程度。它通常为正，因为更高的价格会激励生产者增加供给。
PES = % Change in Quantity Supplied ÷ % Change in Price
If PES > 1, supply is elastic: producers can increase output without a large rise in cost. If PES < 1, supply is inelastic: it is difficult to expand production quickly. Key determinants are the length of the production period, spare capacity, availability of raw materials, and the ease of storing stocks.
如果 PES > 1，供给富有弹性：生产者可以在成本不大幅上升的情况下增加产量。如果 PES < 1，供给缺乏弹性：难以迅速扩大生产。关键决定因素包括生产周期长度、闲置产能、原材料的可获得性以及储存存货的便利程度。
5. Total Revenue and Elasticity | 总收益与弹性
Total revenue is the money a firm receives from selling its output. The relationship between total revenue and price elasticity of demand is critical for pricing decisions.
总收益是企业通过销售产出获得的收入。总收益与需求价格弹性之间的关系对定价决策至关重要。
Total Revenue (TR) = Price × Quantity Sold
If demand is elastic (PED > 1), a price cut raises total revenue because the percentage increase in quantity demanded outweighs the percentage fall in price. If demand is inelastic, a price rise increases total revenue. When demand has unitary elasticity, total revenue is maximised and does not change with small price movements.
如果需求富有弹性（PED > 1），降价会提高总收益，因为需求量增加的百分比超过了价格下降的百分比。如果需求缺乏弹性，提价会增加总收益。当需求是单位弹性时，总收益最大化，且小幅的价格变动不会改变总收益。
6. Costs of Production: Fixed, Variable, Total, Average, Marginal | 生产成本：固定、可变、总、平均与边际
Understanding cost structures helps explain a firm's supply decisions. Costs are classified by their behaviour as output changes.
理解成本结构有助于解释企业的供给决策。成本根据产出变动时的表现进行分类。
Total Cost (TC) = Total Fixed Cost (TFC) + Total Variable Cost (TVC)
Average total cost is TC ÷ Quantity. Average fixed cost (AFC) falls continuously as output rises – this is the spreading effect. Marginal cost (MC) is the extra cost of producing one more unit. The relationship between marginal cost and average cost follows the bathtub curve: when MC is below average total cost, average total cost falls; when MC is above it, average total cost rises.
平均总成本 = TC ÷ 产量。平均固定成本 (AFC) 随产出增加持续下降——这是分摊效应。边际成本 (MC) 是再多生产一单位所带来的额外成本。边际成本与平均成本的关系遵循浴缸曲线：当 MC 低于平均总成本时，平均总成本下降；当 MC 高于平均总成本时，平均总成本上升。
7. Profit Maximisation: Marginal Cost = Marginal Revenue | 利润最大化：边际成本等于边际收益
Economists assume that the main objective of private-sector firms is to maximise profit. This occurs at the output level where the gap between total revenue and total cost is greatest – equivalently, where marginal cost equals marginal revenue.
经济学家假设私营企业的主要目标是利润最大化。这发生在总收益与总成本差距最大的产出水平上——等价于边际成本等于边际收益。
Profit Maximisation Rule: Produce where MC = MR
fect competition, MR equals the market price, so the rule becomes P = MC. A diagram showing the MC and MR curves intersecting, with MC cutting MR from below, is essential for exam answers.
如果在某一产出水平 MR > MC，企业多生产一单位就能增加利润。如果 MC > MR，扩大产出反而会减少利润。在完全竞争市场中，MR 等于市场价格，因此规则变为 P = MC。绘制 MC 与 MR 曲线相交且 MC 从下向上穿过 MR 的图表，是考试答案的关键。
8. Gross Domestic Product and Economic Growth | 国内生产总值与经济增长
Gross Domestic Product measures the total 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.
国内生产总值衡量一个国家在一定时期内生产的所有最终产品和服务的总价值。它可以通过支出法、收入法或产出法来计算。
GDP = C + I + G + (X − M)
ffects of inflation, allowing comparison over time. The economic growth rate is the percentage change in real GDP from one year to the next.
其中 C = 消费，I = 投资，G = 政府支出，X = 出口，M = 进口。实际 GDP 剔除了通货膨胀的影响，便于跨期比较。经济增长率是指实际 GDP 从一年到下一年变化的百分比。
Economic Growth Rate = [(Real GDP Year 2 − Real GDP Year 1) ÷ Real GDP Year 1] × 100
GDP per capita = GDP ÷ Population, which is a rough indicator of average living standards.
人均 GDP = GDP ÷ 人口，是衡量平均生活水平的粗略指标。
9. Unemployment Rate and Labour Force Formulae | 失业率与劳动力相关公式
Unemployment data are central to evaluating the health of an economy. The unemployment rate measures the share of the labour force that is actively seeking work but cannot find it.
失业数据是评估经济运行状况的核心。失业率衡量劳动力中积极寻找工作却未能找到的份额。
Labour Force = Employed + Unemployed
Unemployment Rate = (Number of Unemployed ÷ Labour Force) × 100
des context. When analysing changes, also consider hidden unemployment: those who have given up searching are not counted in the official labour force.
同样，就业率或劳动参与率（劳动力 ÷ 劳动适龄人口 × 100）提供了背景信息。分析变化时，还要考虑隐蔽性失业：放弃寻找工作的人不计入官方劳动力。
10. Inflation: Price Indices and the Inflation Rate | 通货膨胀：价格指数与通胀率
Inflation is a sustained rise in the general price level. It is most commonly measured by the Consumer Price Index (CPI). The Retail Price Index (RPI) is an alternative measure that includes some housing costs.
通货膨胀是总体价格水平的持续上升。它通常用消费者物价指数 (CPI) 来衡量。零售物价指数 (RPI) 是包含部分住房成本的替代指标。
Inflation Rate = [(Price Index Year 2 − Price Index Year 1) ÷ Price Index Year 1] × 100
The CPI uses a fixed basket of goods, weighted according to typical household spending. The weights are updated periodically. Causes of inflation include demand-pull (too much spending chasing too few goods) and cost-push (rising costs of wages, raw materials or energy passed on to consumers).
CPI 使用固定的一篮子商品，并按典型家庭支出加权。权重定期更新。通货膨胀的原因包括需求拉动（过多的支出追逐过少的商品）和成本推动（工资、原材料或能源成本上升转嫁给消费者）。
11. The Multiplier Effect | 乘数效应
The multiplier effect explains how an initial injection of spending into the circular flow can lead to a larger final increase in national income. It works because one person's spending becomes another person's income, leading to further rounds of spending.
乘数效应解释了对循环流的一次初始注入如何导致国民收入最终出现更大的增长。它之所以起作用，是因为一个人的支出成为另一个人的收入，进而引发更多轮次的支出。
Multiplier = 1 ÷ (1 − MPC) = 1 ÷ MPS + MPT + MPM
Here MPC is the marginal propensity to consume, MPS is the marginal propensity to save, MPT is the marginal propensity to tax, and MPM is the marginal propensity to import. The larger the leakages (saving, taxation, imports), the smaller the multiplier. The total change in national income equals the initial injection multiplied by the multiplier.
其中 MPC 是边际消费倾向，MPS 是边际储蓄倾向，MPT 是边际税收倾向，MPM 是边际进口倾向。漏出项（储蓄、税收、进口）越大，乘数越小。国民收入的总变化 = 初始注入 × 乘数。
12. Taxation and Government Budget Balance | 税收与政府预算平衡
Governments raise revenue through direct taxes (e.g. income tax, corporation tax) and indirect taxes (e.g. VAT, excise duties). The budget balance shows the relationship between government spending and tax revenue.
政府通过直接税（如所得税、公司税）和间接税（如增值税、消费税）获取收入。预算平衡显示政府支出与税收收入之间的关系。
Budget Balance = Tax Revenue − Government Spending
A positive balance is a budget surplus; a negative balance is a deficit. A structural deficit remains even when the economy is operating at full capacity. The national debt is the accumulation of past deficits. An understanding of automatic stabilisers (welfare payments and progressive taxes that counteract the business cycle) is often tested alongside these arithmetic relationships.
正余额为预算盈余，负余额为赤字。结构性赤字即使在经济满负荷运行时依然存在。国债是过去赤字的累积。自动稳定器（与经济周期逆向作用的福利支出和累进税）的理解常与这些数量关系一同考查。
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