📚 AP Microeconomics Core Concepts Summary Chart | AP微观经济学核心知识点图表梳理
AP Microeconomics tests your ability to think on the margin, analyze markets, and evaluate government interventions. This article condenses the entire course into a structured summary chart of core concepts, serving as both a quick review and a deep reference.
AP 微观经济学考查你在边际上思考、分析市场以及评估政府干预的能力。本文将整门课程浓缩成一张结构化的核心知识点图表，既是快速复习提纲，也可作为深度参考资料。
1. Basic Economic Concepts | 基本经济概念
Scarcity forces individuals, firms, and governments to make choices that involve trade-offs. The opportunity cost of any decision is the value of the next best alternative forgone.
稀缺性迫使个人、企业和政府做出涉及权衡取舍的选择。任何决策的机会成本都是所放弃的次优选择的价值。
Marginal analysis compares the additional benefit of one more unit with its additional cost. Rational decision makers act when marginal benefit exceeds marginal cost.
边际分析比较增加一单位带来的额外收益与额外成本。当边际收益大于边际成本时，理性决策者便会采取行动。
The production possibilities curve (PPC) illustrates scarcity, efficiency, and opportunity cost. Points inside the curve indicate underutilization, points outside are unattainable without growth.
生产可能性曲线（PPC）展示稀缺性、效率与机会成本。曲线内部的点表示资源未充分利用，外部的点除非经济增长否则无法达到。
| Concept (English) | 中文概念 | Key Insight |
|---|---|---|
| Scarcity | 稀缺性 | Unlimited wants vs. limited resources |
| Opportunity Cost | 机会成本 | Next best alternative given up |
| Marginal Analysis | 边际分析 | MB > MC → take action |
| PPC | 生产可能性曲线 | Shows efficiency, trade-offs, growth |
| Comparative Advantage | 比较优势 | Lower opportunity cost drives trade |
2. Demand and Supply | 需求与供给
The law of demand states that, ceteris paribus, quantity demanded falls when price rises. A change in price causes movement along the curve; a change in non-price determinants (income, tastes, expectations, prices of related goods, number of buyers) shifts the entire demand curve.
需求定律指出，在其他条件不变的情况下，价格上涨时需求量下降。价格变动引起沿需求曲线的移动；非价格决定因素（收入、偏好、预期、相关商品价格、买者数量）的变动会使整条需求曲线移动。
The law of supply states that quantity supplied rises with price. Cost of inputs, technology, taxes/subsidies, expectations, and the number of sellers shift the supply curve.
供给定律指出，供给量随价格上升而增加。投入品成本、技术、税收/补贴、预期和卖者数量会使供给曲线移动。
Market equilibrium occurs where supply and demand intersect. At prices above equilibrium, a surplus drives price down; below equilibrium, a shortage drives price up.
市场均衡出现在供给曲线与需求曲线的交点。价格高于均衡时，出现剩余，推动价格下降；低于均衡时，出现短缺，推动价格上升。
| Shifter (Demand) | 需求曲线移动因素 | Shifter (Supply) | 供给曲线移动因素 |
|---|---|---|---|
| Income (normal vs inferior goods) | 收入（正常品与低档品） | Input prices | 投入品价格 |
| Price of substitutes / complements | 替代品/互补品价格 | Technology | 技术 |
| Tastes and preferences | 偏好 | Taxes and subsidies | 税收与补贴 |
| Expectations, number of buyers | 预期、买者数量 | Number of sellers, expectations | 卖者数量、预期 |
3. Elasticity | 弹性
Price elasticity of demand (PED) measures responsiveness of quantity demanded to price changes. PED = (%ΔQd) / (%ΔP). Elastic demand (|PED| > 1) means consumers are sensitive to price; inelastic demand (|PED| < 1) means they are less responsive.
需求的价格弹性（PED）衡量需求量对价格变化的反应程度。PED = (%ΔQd) / (%ΔP)。富有弹性（|PED| > 1）表示消费者对价格敏感；缺乏弹性（|PED| < 1）表示反应较小。
Key determinants include availability of substitutes, whether the good is a necessity or luxury, share of income, and time horizon. Total revenue test: if price and total revenue move in opposite directions, demand is elastic.
关键决定因素包括替代品的可获得性、商品是必需品还是奢侈品、在收入中所占比重以及时间长短。总收益检验：如果价格与总收益反向变动，则需求富有弹性。
Income elasticity (YED) identifies normal goods (positive YED) and inferior goods (negative YED). Cross-price elasticity (XED) distinguishes substitutes (positive) from complements (negative). Price elasticity of supply (PES) depends on production flexibility and time.
收入弹性（YED）识别正常品（正的 YED）与低档品（负的 YED）。交叉价格弹性（XED）区分替代品（正值）与互补品（负值）。供给的价格弹性（PES）取决于生产的灵活性与时间。
| Elasticity Type | 弹性类型 | Formula | Interpretation |
|---|---|---|---|
| PED | 需求价格弹性 | (%ΔQd)/(%ΔP) | |PED|>1 elastic; <1 inelastic; =1 unit elastic |
| YED | 需求收入弹性 | (%ΔQd)/(%ΔIncome) | Positive: normal; negative: inferior |
| XED | 需求交叉弹性 | (%ΔQd good A)/(%ΔP good B) | Positive: substitutes; negative: complements |
| PES | 供给价格弹性 | (%ΔQs)/(%ΔP) | Depends on spare capacity, time period |
4. Market Equilibrium and Efficiency | 市场均衡与效率
Consumer surplus is the difference between what buyers are willing to pay and the market price; producer surplus is the difference between the market price and the minimum price sellers require. Total surplus is maximized at competitive equilibrium, signalling allocative efficiency.
消费者剩余是买者愿意支付的最高价格与市场价格之间的差额；生产者剩余是市场价格与卖者能接受的最低价格之间的差额。在竞争性均衡处总剩余最大化，表明配置效率的实现。
Deadweight loss arises when output deviates from the efficient quantity due to price controls, taxes, subsidies, or monopoly. A price ceiling below equilibrium creates a shortage; a price floor above equilibrium generates a surplus.
当产量因价格管制、征税、补贴或垄断而偏离有效数量时，会产生无谓损失。低于均衡价格的最高限价造成短缺；高于均衡价格的最低限价造成过剩。
An excise tax shifts the supply curve upward by the tax amount. It creates a wedge between buyer and seller prices, reduces quantity, and generates deadweight loss. The tax burden is shared according to relative elasticities.
消费税使供给曲线向上移动，幅度为税额。它在买方价格与卖方价格之间插入楔子，减少交易量并产生无谓损失。税收负担按相对弹性分配。
| Intervention | 干预措施 | Effect on Price | Effect on Quantity | Deadweight Loss? |
|---|---|---|---|---|
| Price Ceiling (binding) | 有效最高限价 | Below equilibrium | Shortage (Qs < Qd) | Yes |
| Price Floor (binding) | 有效最低限价 | Above equilibrium | Surplus (Qs > Qd) | Yes |
| Per-unit Tax | 从量税 | Buyer pays Pb, seller receives Ps; Pb > Ps | Decreases | Yes |
| Per-unit Subsidy | 从量补贴 | Buyer pays less, seller receives more | Increases beyond efficient level | Yes (overproduction) |
5. Consumer Choice Theory | 消费者选择理论
Utility represents satisfaction from consumption. The law of diminishing marginal utility states that as more of a good is consumed, the additional satisfaction from each extra unit eventually declines.
效用代表消费带来的满足感。边际效用递减规律指出，随着某种商品消费量的增加，每额外一单位带来的满足感最终会下降。
Consumers maximize total utility when the marginal utility per dollar spent is equal across all goods: MUa/Pa = MUb/Pb. This optimal consumption rule ensures that the last dollar spent on each good yields the same additional utility.
消费者在每种商品上花费的每一美元的边际效用相等时实现总效用最大化：MUa/Pa = MUb/Pb。这一最优消费规则保证了花在每种商品上的最后一美元带来相同的额外效用。
A price drop triggers the substitution effect (consumers buy more of the cheaper good, less of its substitutes) and the income effect (purchasing power rises, affecting normal and inferior goods differently).
价格下降引发替代效应（消费者多买变便宜的商品，少买其替代品）和收入效应（购买力上升，对正常品与低档品的影响不同）。
The budget constraint shows affordable combinations of two goods. Its slope equals the relative price -Px/Py. A change in income shifts the line; a change in relative prices pivots it.
预算约束线表示两种商品的可负担组合。其斜率等于相对价格 -Px/Py。收入变动使约束线平移；相对价格变动使其旋转。
| Key Element | 关键要素 | Explanation |
|---|---|---|
| Marginal Utility (MU) | 边际效用 | Change in total utility from one more unit |
| Optimal Consumption Rule | 最优消费规则 | MUx/Px = MUy/Py |
| Substitution Effect | 替代效应 | Relative price change alters consumption mix |
| Income Effect | 收入效应 | Change in real purchasing power |
6. Costs of Production | 生产成本
In the short run, at least one input is fixed. Total cost (TC) = Total Fixed Cost (TFC) + Total Variable Cost (TVC). Average total cost (ATC) = TC / Q = AFC + AVC. Marginal cost (MC) is the addition to total cost from producing one more unit.
在短期，至少有一种投入品固定不变。总成本（TC）= 总固定成本（TFC）+ 总可变成本（TVC）。平均总成本（ATC）= TC / Q = 平均固定成本（AFC）+ 平均可变成本（AVC）。边际成本（MC）是额外生产一单位产品所带来的总成本增加量。
The marginal cost curve eventually rises due to diminishing marginal returns. MC intersects ATC and AVC at their minimum points. When MC is below ATC, ATC falls; when MC is above ATC, ATC rises.
由于边际报酬递减，边际成本曲线最终上升。MC 与 ATC 和 AVC 相交于它们的最低点。当 MC 低于 ATC 时，ATC 下降；当 MC 高于 ATC 时，ATC 上升。
In the long run, all inputs are variable. Economies of scale cause LRATC to decline as output expands; diseconomies of scale cause it to rise. Constant returns to scale leave LRATC flat.
长期中所有投入品均可变。规模经济使得长期平均总成本（LRATC）随着产量扩大而下降；规模不经济使其上升；规模报酬不变使 LRATC 持平。
| Cost Concept | 成本概念 | Formula / Behavior |
|---|---|---|
| TFC | 总固定成本 | Constant regardless of output |
| TVC | 总可变成本 | Increases with Q, initially at decreasing rate |
| ATC = AFC + AVC | 平均总成本 | U-shaped; MC crosses at minimum |
| MC | 边际成本 | Change in TC / Change in Q |
| LRATC | 长期平均总成本 | Envelope of SRATC curves; shows scale effects |
7. Perfect Competition | 完全竞争市场
A perfectly competitive market has many buyers and sellers, identical products, no barriers to entry or exit, and perfect information. Firms are price takers: they face a perfectly elastic demand curve at the market price (P = MR).
完全竞争市场拥有众多买者与卖者、同质产品、无进入或退出壁垒以及完全信息。企业是价格接受者：它们面对的是在市场价格处的完全弹性需求曲线（P = MR）。
Firms maximize profit where MR = MC. In the short run, a firm can earn economic profit or incur a loss but will shut down if price falls below AVC. The short-run supply curve is the MC curve above AVC.
企业在 MR = MC 处实现利润最大化。短期内，企业可能获得经济利润或承受亏损，但如果价格低于 AVC 就会停产。短期供给曲线是 AVC 以上的 MC 曲线部分。
In the long run, entry and exit drive economic profit to zero. Firms produce at the minimum point of ATC, achieving both productive and allocative efficiency (P = MC).
长期中，进入与退出使经济利润趋于零。企业在 ATC 的最低点生产，同时实现了生产效率和配置效率（P = MC）。
| Time Horizon | 时期 | Profit Condition | Efficiency |
|---|---|---|---|
| Short Run | 短期 | Possible economic profit or loss; operate if P > AVC | Not guaranteed |
| Long Run | 长期 | Zero economic profit (normal profit only) | Productive (P = min ATC) and allocative (P = MC) |
8. Imperfect Competition: Monopoly, Monopolistic Competition, Oligopoly | 不完全竞争：垄断、垄断竞争、寡头
A monopoly is a single seller with high barriers to entry. The monopolist faces the downward-sloping market demand curve, so price exceeds marginal revenue (P > MR). Profit maximization occurs at MR = MC, but the price is then set on the demand curve, creating deadweight loss.
垄断是存在高进入壁垒的单一卖者。垄断者面对向下倾斜的市场需求曲线，因此价格高于边际收益（P > MR）。利润最大化在 MR = MC 处实现，但价格则根据需求曲线设定，产生无谓损失。
Monopolies can practice price discrimination by charging different prices to consumers with different elasticities. Perfect price discrimination captures all consumer surplus and eliminates deadweight loss, but is rare.
垄断者可实行价格歧视，向不同弹性的消费者收取不同价格。完全价格歧视攫取全部消费者剩余并消除无谓损失，但这种情况很少见。
Monopolistic competition features many firms, differentiated products, and easy entry. In the short run, firms behave like monopolists; in the long run, entry shifts demand left until firms earn zero economic profit, producing with excess capacity (not at min ATC).
垄断竞争具有众多企业、产品差异化以及容易进入的特征。短期内企业如同垄断者一样行动；长期中进入使需求曲线左移，直至企业获得零经济利润，并存在过剩产能（不在 ATC 最低点生产）。
Oligopoly is dominated by a few interdependent firms. Game theory models strategic behavior: the prisoner’s dilemma explains why collusion may break down. Nash equilibrium occurs when each firm chooses its best strategy given the other’s actions.
寡头市场由少数几家相互依存的企业主导。博弈论模型用于分析策略行为：囚徒困境解释了为何合谋可能破裂。给定对方策略，每个企业选择最优策略时达到纳什均衡。
| Structure | 市场结构 | Number of Firms | Product | Efficiency |
|---|---|---|---|---|
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