Sellers and Incentives

Introduction

This chapter explores the behavior of sellers in perfectly competitive markets, focusing on how they make production decisions, calculate costs and revenues, and respond to incentives. It also examines the derivation of the supply curve, the concept of producer surplus, and the transition from short-run to long-run equilibrium.

Sellers in a Perfectly Competitive Market

Conditions of Perfect Competition

• No individual buyer or seller can influence the market price: The market consists of many buyers and sellers, each too small to affect the price.

• Identical goods: All sellers offer products that are perfect substitutes.

• Free entry and exit: Firms can freely enter or leave the market in response to profit opportunities.

Example: Corn and soybean markets, where individual farmers cannot affect the market price and can enter or exit based on profitability.

The Seller’s Problem

Three Key Questions

• How to make the product? (Production process: transforming inputs into outputs)

• What is the cost of making the product? (Cost analysis: fixed and variable costs)

• How much can the seller get for the product in the market? (Revenue: determined by market price and quantity sold)

Production Concepts

• Physical capital: Machines, buildings, and other equipment used in production.

• Short run: Some inputs (e.g., capital) are fixed; only variable inputs (e.g., labor) can be changed.

• Long run: All inputs can be adjusted.

• Variable factor of production: Input that can be changed in the short run (e.g., labor).

• Fixed factor of production: Input that cannot be changed in the short run (e.g., factory size).

Marginal Product and the Law of Diminishing Returns

• Marginal product: The additional output produced by using one more unit of input.

• Specialization: Marginal product increases initially as workers specialize.

• Law of diminishing returns: Eventually, adding more of a variable input leads to smaller increases in output, and marginal product can even become negative if too many workers are added.

Cost Concepts

• Total cost (TC): The sum of variable and fixed costs.

• Variable cost (VC): Costs that change with the level of output (e.g., wages).

• Fixed cost (FC): Costs that do not change with output (e.g., rent).

• Average total cost (ATC):

• Average variable cost (AVC):

• Average fixed cost (AFC):

• Marginal cost (MC):

Revenue and Profit

• Total revenue (TR):

• Profit (\pi):

• Accounting profit: Total revenue minus explicit costs.

• Economic profit: Total revenue minus explicit and implicit (opportunity) costs.

Profit Maximization

• The profit-maximizing output is where marginal revenue (MR) equals marginal cost (MC).

• In perfect competition, .

• Profit-maximizing rule:

Calculating Profit

• Profit can also be calculated as:

• If , the firm earns economic profit; if , it incurs economic loss; if , it breaks even.

From the Seller’s Problem to the Supply Curve

Supply Curve Derivation

• The supply curve is the portion of the marginal cost curve above the average variable cost (AVC).

• Firms will only supply output if the market price is at least equal to AVC in the short run.

Price Elasticity of Supply

• Price elasticity of supply (): Measures how responsive quantity supplied is to a change in price.

• Formula:

• Elastic supply: ; Inelastic supply: ; Unit-elastic supply:

Shutdown Decision

• A firm should shut down in the short run if .

• Fixed costs are sunk in the short run and should not affect the shutdown decision.

Producer Surplus

Definition and Measurement

• Producer surplus: The difference between the market price and the minimum price at which a firm would be willing to sell (represented by the supply curve).

• Graphically, it is the area above the supply (MC) curve and below the market price.

• For a linear supply curve, producer surplus is the area of a triangle:

From the Short Run to the Long Run

Short Run vs. Long Run

• Short run: Some inputs are fixed; firms can only adjust variable inputs.

• Long run: All inputs are variable; firms can enter or exit the market.

Returns to Scale

• Economies of scale: ATC decreases as output increases (e.g., due to specialization or large set-up costs).

• Constant returns to scale: ATC remains unchanged as output increases.

• Diseconomies of scale: ATC increases as output increases (e.g., due to management inefficiencies).

From the Firm to the Market: Long-Run Competitive Equilibrium

Entry and Exit

• In the long run, firms enter the market if there are economic profits and exit if there are economic losses.

• Entry and exit drive economic profit to zero in the long-run equilibrium (firms earn normal profit).

• The long-run supply curve is typically horizontal (perfectly elastic) at the minimum ATC.

Evidence-Based Economics: Ethanol Subsidies

Application: Subsidies and Market Entry

• Subsidies increase short-run profits, attracting new firms to enter the market.

• As more firms enter, market supply increases, driving down the price and reducing profits until only normal profit remains in the long run.

Key Formulas and Tables

Summary Table: Cost Concepts

Summary Table: Types of Profit

Additional info: These notes synthesize textbook slides and tables, expanding on definitions, formulas, and applications for clarity and exam preparation.