AP 微观经济——自己的复习笔记

[Unit 2] Factors of Production

（From PPT 10.1）

• Land: All natural resources that are used to produce goods and services.
• Labor: Any effort a person devotes to a task for which that person is paid.
• Capital:
  • Physical Capital: Any human-made resource that is used to create other goods and services.
  • Human Capital: Any skills or knowledge gained by a worker through education and experience.
• * Entrepreneurship: Ambitious leaders that combine the other factors of production to create goods and services.

[Unit 4] The Law of Demand

（书 P70）

• The Income Effect
  • 价格上涨让人无法负担。
• The Substitution Effect
  • 价格变化让人转向替代品。
• Diminishing Marginal Utility

[Unit 5] Elasticity

Price Elasticity of Supply

\[PES = \frac {\% \Delta Q} {\% \Delta P} \]

---

Price Elasticity of Demand

\[PED = \frac {\% \Delta Q} {\% \Delta P} \]

Cross-price elasticity of demand

\[XED = \frac {\% \Delta Q_X} {\% \Delta P_Y} \]

\[XED \begin{cases}\text{Complements} & < 0 \\\text{Substitutes} & > 0 \\ \end{cases}\]

Income Elasticity of Demand

\[YED = \frac {\% \Delta Q} {\% \Delta \text{Income}} \]

\[YED \begin{cases}\text{Inferior} & < 0 \\\text{Normal} & > 0 \\ \end{cases}\]

[Unit 6] Costs of Production

Production Function

（书 P123）

三个阶段：

1. TP↑ MP↑ - increasing marginal returns
2. TP↑ MP↓ - diminishing marginal returns
3. TP↓ MP↓ - negative marginal returns

MC 与 MP，AVC 与 AP 互为 mirror images。（个人感觉这个说法纯扯淡，只是表明趋势相反）

LRATC

三个阶段：

1. Economies of Scale
2. Constant Returns to Scale
3. Diseconomies of Scale

The law of diminishing marginal returns doesn’t apply in the long run because there are NO FIXED RESOURCES.

Returns to Scale

（书 P TODO:）

If a Firm Doubles All Inputs Used in Production . . .

• and output more than doubles, the firm is experiencing increasing returns to scale.
• and output less than doubles, it is decreasing returns to scale.
• and output doubles, it is experiencing constant returns to scale.

[Unit 8] Price Discrimination

（PPT 8.2）

\(D = MR\)

Graph

• Profit 是梯形状的。
• 没有 CS
• 没有 DWL

[Unit 8] Natural Monopoly

（PPT 8.3）

只有 Long Run 哦！

Characteristics

• one firm in the market (Firm = MKT)
• realizes economies of scale
  • LRATC continues to decrease as output increases
• Barrier: significant high fixed costs (government)

Graph

• ATC 和 MC 都往下跑的。
• \(MR = MC\)：Unregulated Pricing
  • Market Price
  • Profit!
• \(ATC = D\)：Fair-Return Pricing
  • Breakeven
• \(MC = D\)：Socially Optimal Pricing
  • Equilibrium
  • Loss!

[Unit 9] Monopolistic Competition

（PPT 9.1）

Characteristics

• Differentiated product
• A large number of producers
• Price Takers *some control over price
• Low Barriers
• Inefficiency
  • 既不是 Allocative Efficiency 又不是 Productive Efficiency
    • 有 DWL
  • Excess Capacity：实际生产（\(MR=MC\)）Quantity 与 Productive Efficiency Quantity 的差。

Long Run 怎么平衡

• 一开始是盈利的
  • 盈利，而且 low barriers，所以会有一车 Firm 涌进来，每个 Firm 的 \(D\) 和 \(MR\) 都下降了（Market Share 下降）。
• 一开始是亏损的
  • 有 Loss 就会有人被挤出去，\(D\) 和 \(MR\) 上升。

因此最终 \(D\) 会卡在刚好和 \(ATC\) 相切的地方。

[Unit 10] Labor MKT

（PPT 10.1 & 10.2）

Key Concepts

• Derived Demand The demand for a resource is derived from the demand for a product to
  which the resource has contributed.
• MRP (Marginal Revenue Product): the addition to a firm’s revenue when an additional input is employed.
• MFC / MRC (Marginal Factor Cost / Marginal Resource Cost): the additional cost of employing an additional input like a machine or worker.

\[\boxed{MRP = \frac {\Delta TR} {\Delta Input} = MR \times MP} \]

\[\boxed{MFC = \frac {\Delta TC} {\Delta Input} = Wage} \]

💡 \(MRP = \frac {dTR} {dL}\)，\(MFC = \frac {dTC} {dL}\)

Profit-Maximizing Rule for Employing Resources

\[\boxed{MRP = MFC} \]

Perfectly Competitive Labor MKT

Characteristics

• Many small firms are hiring workers
• Many workers with identical skills
• Wage is constant
• Workers are wage takers

Graph

（书 P184）

• 市场（Labor MKT）是正常的 S and D。
  • 纵轴是 Wage，横轴是 Quantity of Labor。
• Firm 的 Supply 是横的，Demand 是斜的。
  • S = MFC, D = MRP。

Minimum Wage

MKT 会出现 Surplus，Firm 的 MFC 抬高，quantity 减少。

Shifters (Demand)

• Changes in the Product Demand
• Changes in Productivity
  • e.g. Tech
• Changes in Price of others
  • Substitute Resource / Complement Resource

Least-Cost Rule

（书 P186）

\[\boxed{\frac {MP_1} {P_1} = \frac {MP_2} {P_2}} \]

（PPT 10.2）

\[\boxed{\frac {MRP_1} {MFC_1} = \frac {MRP_2} {MFC_2} = 1} \]

Monopsony

A single buyer.

Graph

⚠️易错

• D 是正常的 MRP，向下走。
• S 向上走。
• MFC 斜率是 S 的两倍。
• 实际雇佣的 Quantity 是 \(Q@MFC=MRP\)。
• 实际的 Wage 是 \(Q\) 对应 S 上的 Price（不是 MRP！）。

[Unit 11] Coase Theorem

（PPT 11）

课上讲过吗？

condition:

• Number of people involved is small
• Bargaining costs are negligible (low)
• Property ownership is clearly defined

believes private parties involved can solve the issues created by externalities (negative) on their own.

[Unit 11] Private & Public Goods

• Public goods: nonexclusive & nonrival
  • Free-rider problem
• Private goods: exclusive & rival

(Khan Academy)

• Rival: One person using it impairs another person using it
• Exclusive: Can stop someone from using it

	Exclusive	Nonexclusive
Rival	Private Goods	(Common Resource)
Nonrival	(Artificially Scarce)	Public Goods

e.g.

	Exclusive	Nonexclusive
Rival	Clothing	Timber
Nonrival	Satellite TV	National Defense

[Unit 11] Types of Taxes

• progressive tax
  • takes a larger percent of income from high income groups
  • takes more from rich people
• proportional tax
  • takes the same percent of income from all income groups
• regressive tax
  • takes a larger percentage from low income groups
  • takes more from poor people