Competitive Firms and Markets: Study Notes

Competitive Firms and Markets

Market Structure

Market structure refers to the characteristics of a market that influence the behavior and performance of firms within it. Understanding market structure is essential for analyzing how firms compete and set prices.

• Market Structure: Defined by the number of firms, ease of entry and exit, and product differentiation.

• Competitive Market Structure: Many firms produce identical products, and entry and exit are easy.

Price Taking and the Firm's Demand Curve

In a competitive market, firms are price takers, meaning they cannot influence the market price and must accept it as given.

• Price Taker: A firm that cannot significantly affect the market price for its output or input prices.

• The demand curve facing a price-taking firm is horizontal at the market price.

Characteristics of Perfect Competition:

• Many small buyers and sellers

• Identical products

• Full information about prices and products

• Negligible transaction costs

• Free entry and exit

Deviations from Perfect Competition

Many real-world markets are not perfectly competitive but are still highly competitive if no buyer or seller can affect the market price.

• Competitive Market: All participants are price takers, even if not all conditions of perfect competition are met.

Residual Demand Curve

The residual demand curve shows the market demand not met by other sellers at any given price.

• Residual Demand Curve: The demand remaining for a firm after accounting for the supply of other firms.

Elasticity of Residual Demand:

• If the market has n identical firms, the elasticity of demand facing Firm i is:

$\varepsilon_i = n \varepsilon - (n-1) \eta$

• Where $\varepsilon$ is the market elasticity of demand (negative), $\eta$ is the elasticity of supply of other firms (positive), and $n$ is the number of firms.

Example: In the Canadian metal chair market with 78 firms, the residual demand elasticity facing a single firm is nearly 300 times the market elasticity, making the firm's demand curve highly elastic (almost perfectly horizontal).

Why Study Perfect Competition?

Perfect competition serves as a benchmark for analyzing real-world markets, especially those with many firms and standardized products (e.g., agriculture, commodities, stock exchanges).

Profit Maximization

Economic Profit and Opportunity Cost

Firms seek to maximize economic profit, which considers both explicit and implicit costs (opportunity costs).

• Economic Profit: Revenue minus total economic cost (includes opportunity cost).

• Opportunity Cost: Value of the best alternative use of resources.

Profit Maximization Decisions

Firms must make two key decisions to maximize profit:

• Output Decision: What output level maximizes profit or minimizes loss?

• Shutdown Decision: Is it more profitable to produce or to shut down?

Output Decision Rules

• Rule 1: Set output where profit is maximized.

• Rule 2: Set output where marginal profit is zero.

• Rule 3: Set output where marginal revenue equals marginal cost:

$MR = MC$

• Marginal Revenue (MR): Change in revenue from selling one more unit.

• Marginal Profit: Change in profit from selling one more unit.

Shutdown Decision Rules

• Rule 1: Shut down only if it reduces loss.

• Rule 2: Shut down if revenue is less than avoidable (variable) cost.

Example: If revenue is $2,000, variable cost is $1,000, and fixed cost is $3,000, shutting down would result in a loss equal to the fixed cost ($3,000). If operating, the loss is $2,000 (revenue) - $1,000 (variable cost) - $3,000 (fixed cost) = -$2,000. Thus, it is better to operate.

Short-Run Output and Shutdown Decisions

• In the short run, a competitive firm's marginal revenue equals the market price.

$P = MC$

• A firm shuts down if the market price is less than its short-run average variable cost (AVC) at the profit-maximizing quantity.

$P < AVC_{min}$

Effect of Fixed Costs

• Changes in fixed costs do not affect the firm's output decision in the short run.

• Only variable costs influence the shutdown decision.

Short-Run Supply

Short-Run Firm Supply Curve

The short-run supply curve for a competitive firm is its marginal cost curve above the minimum average variable cost.

• If price falls below minimum AVC, the firm shuts down.

Short-Run Market Supply

• With n identical firms, market supply at any price is $n$ times the supply of an individual firm.

• As the number of firms increases, the market supply curve becomes flatter (more elastic).

Short-Run Equilibrium

Market equilibrium occurs where market supply equals market demand. Taxes or other shocks can shift supply or demand, affecting equilibrium price and quantity.

Long-Run Competition

Long-Run Profit Maximization

• Firms maximize profit where marginal revenue equals long-run marginal cost:

$MR = LMC$

• In the long run, all costs are variable, and firms can enter or exit the market.

Long-Run Firm Supply Curve

• The long-run supply curve is the long-run marginal cost curve above the minimum of the long-run average cost curve.

• Firms can adjust all inputs, including capital, in the long run.

Long-Run Market Supply Curve

• The market supply curve is the horizontal sum of individual firm supply curves.

• Entry and exit of firms ensure that, in the long run, firms earn zero economic profit (normal profit).

Entry and Exit

• Firms enter if they can earn positive long-run profit.

• Firms exit if they would incur a long-run loss.

• With free entry and exit, the long-run market supply curve is flat at the minimum long-run average cost if all firms are identical and input prices are constant.

Upward-Sloping Long-Run Supply Curves

Several factors can cause the long-run market supply curve to slope upward:

• Limited Entry: Government restrictions, scarce resources, or costly entry limit the number of firms.

• Cost Differences: Firms with different cost structures enter at different prices.

• Rising Input Prices: Input prices increase as industry output rises.

• Large Buyers: A large buyer can affect the market supply curve by demanding a significant share of output.

Residual Supply Curve

• Residual Supply Curve: The quantity supplied to a market not consumed by other demanders at a given price.

$S^r(p) = S(p) - D^O(p)$

• Where $S^r(p)$ is the residual supply, $S(p)$ is total supply, and $D^O(p)$ is demand from other buyers.

Long-Run Competitive Equilibrium

• Determined by the intersection of long-run market supply and demand curves.

• Equilibrium price equals minimum long-run average cost.

• A shift in demand affects equilibrium quantity but not the long-run equilibrium price (if supply is perfectly elastic).

Summary Table: Short-Run vs. Long-Run Competitive Supply

Feature	Short Run	Long Run
Entry/Exit	Number of firms fixed	Firms can enter/exit freely
Supply Curve	Sum of MC above AVC for all firms	Sum of LMC above minimum LAC for all firms
Profit	Firms can earn profit or loss	Firms earn zero economic profit
Fixed Costs	Some costs fixed	All costs variable

Key Formulas

• Profit: $\pi = R - C$

• Marginal Revenue: $MR = \frac{dR}{dq}$

• Marginal Cost: $MC = \frac{dC}{dq}$

• Shutdown Condition (Short Run): $P < AVC_{min}$

• Residual Supply: $S^r(p) = S(p) - D^O(p)$

Applications and Examples

• Tax Incidence: A per-unit tax collected from all firms shifts the supply curve upward by the amount of the tax, affecting equilibrium price and quantity.

• Special Markets: In markets with special regulations (e.g., special-blend gasoline), supply is less elastic, so price increases more when demand rises.

Additional info: Some formulas and explanations were expanded for clarity and completeness, and a summary table was constructed to compare short-run and long-run supply.