Perfect Competition: Short-Run and Long-Run Analysis

Perfect Competition

Introduction to Perfect Competition

Perfect competition is a market structure characterized by many firms selling identical products, where no single firm can influence the market price. This topic is foundational in microeconomics and is essential for understanding market efficiency and firm behavior in both the short and long run.

• Identical Products: All firms sell products that are perfect substitutes for each other.

• Price Takers: Individual firms accept the market price as given; they cannot influence it.

• Free Entry and Exit: Firms can freely enter or leave the market in the long run.

• Perfect Information: Both firms and consumers have complete knowledge about prices and products.

• Example: Stock exchanges like the JSE (Johannesburg Stock Exchange) are often cited as real-world approximations of perfect competition.

Profit Maximization in the Short Run

Profit Maximization Condition

In the short run, a perfectly competitive firm maximizes profit or minimizes loss by choosing the output level where marginal cost (MC) equals marginal revenue (MR). Since the firm is a price taker, price (P) also equals MR.

• Profit Maximization Rule: $P = MR = MC$

• If MC > MR: The cost of producing an additional unit exceeds the revenue, so the firm should reduce output.

• If MR > MC: The revenue from an additional unit exceeds the cost, so the firm should increase output.

• Efficient Allocation: Occurs when $P = MC$, meaning resources are allocated to their most valued use.

Short-Run Outcomes

Depending on market price and cost structure, a perfectly competitive firm can experience economic profit, normal profit, or a loss in the short run.

• Economic Profit: Occurs when $P > ATC$ (Average Total Cost).

• Normal Profit: Occurs when $P = ATC$; the firm covers all costs, including opportunity costs.

• Loss: Occurs when $P < ATC$; the firm may continue to operate if $P AVC$ (Average Variable Cost), but will shut down if $P < AVC$.

Calculation Example

• Given: $P = 600 - 4Q$ (Demand), $P = 20 + 1.8Q$ (Supply), $TC = 5Q^2 + 10Q + 190$

• Marginal Cost (MC): $MC = \frac{d(TC)}{dQ} = 10Q + 10$

• Average Total Cost (ATC): $ATC = \frac{TC}{Q}$

• Profit: $\text{Profit} = TR - TC$ where $TR = P \times Q$

Additional info: Students should practice calculating MC, ATC, and profit using the provided functions and plot these on a graph to visualize profit-maximizing output.

Long-Run Adjustments and Equilibrium

Long-Run Equilibrium

In the long run, firms can enter or exit the market. The process continues until firms make normal profit, and no incentive exists for entry or exit.

• Condition: $P = ATC = MC = MR$

• Allocative Efficiency: Achieved when $P = MC$

• Productive Efficiency: Achieved when firms produce at the minimum point of the ATC curve

• SRATC = LRATC: At the equilibrium output, short-run and long-run average total costs are equal

Market Efficiency in Perfect Competition

Reasons for Efficiency

• Productive Efficiency: Firms produce at the lowest possible cost (minimum ATC)

• Allocative Efficiency: Resources are allocated such that $P = MC$

• Maximized Surplus: The sum of consumer and producer surplus is maximized

• Normal Profit in the Long Run: $P = ATC$

Long-Run Market Supply Curve

Types of Cost Industries

The shape of the long-run supply curve depends on how input costs change as industry output changes.

Industry Type	Cost Behavior	Long-Run Supply Curve	Price Adjustment
Constant Cost	ATC does not change as output changes	Horizontal	Price returns to original level after demand increase
Increasing Cost	ATC rises as output increases	Upward sloping	Price settles above original level after demand increase
Decreasing Cost	ATC falls as output increases	Downward sloping	Price settles below original level after demand increase

Constant Cost Industry

• Definition: Input prices and ATC remain unchanged as industry output changes.

• Long-Run Supply: Horizontal at the minimum LAC (Long-Run Average Cost).

Increasing Cost Industry

• Definition: Input prices and ATC rise as industry output increases.

• Long-Run Supply: Upward sloping; price increases with output.

Decreasing Cost Industry

• Definition: Input prices and ATC fall as industry output increases.

• Long-Run Supply: Downward sloping; price decreases with output.

Additional info: The long-run supply curve's slope reflects how input costs respond to industry expansion or contraction, influencing market price adjustments after demand changes.