Characteristics of perfectly competitive markets

Perfect competition describes an ideal market structure where specific conditions lead to efficient outcomes. Although no real markets fully match this model, it helps explain issues in actual markets that cause problems like high prices or limited choice.

Key features of perfect competition

• Large number of buyers and sellers - Markets have countless suppliers and consumers, meaning no single firm or buyer can influence prices on their own.
• Price takers - Firms accept the market price set by overall supply and demand, rather than setting their own prices.
• Perfect information - Both buyers and sellers know all details about products, prices, and production methods, ensuring informed decisions without hidden advantages.
• Homogeneous products - All goods are identical, with no branding or differences, making them perfect substitutes that consumers can easily switch between.
• No barriers to entry or exit - New firms can join the market freely, and existing ones can leave without restrictions.
• Profit maximisation - Firms aim to maximise profits by producing where marginal cost (MC) equals marginal revenue (MR).

Allocative efficiency in perfect competition

Allocative efficiency happens when resources are distributed to match what society values most, ensuring goods are produced at the right quantity and price.

How perfect competition achieves allocative efficiency

In perfectly competitive markets, prices act perfectly as signals, incentives, and rationing tools. The market demand curve reflects marginal utility (MU), showing the value consumers place on extra units. The supply curve matches marginal cost (MC), indicating production costs.

At equilibrium, price (P) equals MC and MU, meaning firms supply exactly what consumers want without waste.

Allocative efficiency and externalities

While perfect competition promotes efficiency, external factors can disrupt this balance. Externalities are costs or benefits affecting third parties not involved in the transaction.

Impact of externalities on efficiency

Perfect competition assumes no externalities, achieving efficiency where price equals marginal social cost (MSC), which includes all societal costs. However, firms focus on marginal private cost (MPC), ignoring external effects.

With negative externalities, like pollution, MPC is less than MSC, causing prices to be too low. This leads to overproduction and overconsumption, creating inefficiency.

Supernormal profits and long-run equilibrium

Supernormal profits are earnings above normal levels, but perfect competition prevents them from lasting due to market forces.

How supernormal profits are eliminated

Firms calculate profit as total revenue (TR) minus total costs (TC), where TR is quantity (Q) times price (P), and TC is Q times average cost.

$\text{Profit}=\text{TR}-\text{TC}$

Short-run supernormal profits draw new firms into the market, shifting supply rightward and lowering prices. This competition erodes profits until only normal profits remain.

In the long run, equilibrium occurs at the lowest point of the average cost (AC) curve, achieving productive efficiency. Here, P equals MC, ensuring allocative efficiency.

Market exit in perfect competition

Firms may leave markets when profits fall below sustainable levels, helped by the lack of exit barriers.

Conditions for market exit

If average revenue (AR), or price, drops below average cost (AC), firms make losses instead of normal profits.

In the long run, persistent losses lead to exit, reducing supply and raising prices until remaining firms break even.

Short-run decisions depend on costs:

• Above average variable costs (AVC) - Firms may stay temporarily to cover some fixed costs.
• Below AVC - Immediate exit occurs, as continuing would increase losses.