6.1

Socially Efficient and Inefficient Market Outcomes

AP Microeconomics

Efficiency Review

Private vs. Social Costs and Benefits

Marginal Private Benefit (MPB) The benefit to the **buyer** from consuming one more unit. This is the **demand curve**.

Marginal Private Cost (MPC) The cost to the **seller** from producing one more unit. This is the **supply curve**.

Marginal Social Benefit (MSB) The total benefit to **society** from one more unit:

Marginal Social Cost (MSC) The total cost to **society** from one more unit:

When Is the Market Efficient?

When Does Market Failure Occur?

Negative Externality (Overproduction)

DWL12345678910123456789101112Quantity$/unitMarket Q (too much)Socially optimal QMPC (Supply)MSC = MPC + MECMPB = MSB (D)

Negative externality: market overproduces — DWL from units between Qsocial and Qmarket

Positive Externality (Underproduction)

DWL12345678910123456789101112131415Quantity$/unitMarket Q (too little)Socially optimal QMPC = MSC (Supply)MPB (D)MSB = MPB + MEB

Positive externality: market underproduces — DWL from units not produced between Qmarket and Qsocial

Total Surplus Analysis

The Role of Government

AP Exam Tips

Common Mistakes