Long Run Supply, Efficiency, and Welfare in Perfect Competition

Relationship Between Price, Cost, and Profitability in the Short Run

• Economic Profit Conditions     * Economic profit occurs when the market price ($P$) lies above the Average Cost ($AC$) curve.     * There is a distinct relationship between price and quantity at this level, and the firm will definitely produce.

• Normal Profit Conditions     * Normal profit is achieved when the price ($P$) is tangent to the Average Cost ($AC$) curve.     * This represents the break-even point where all costs (including implicit costs) are covered.

• Loss Minimizing Output     * A firm is in a loss-minimizing state when the Average Cost ($AC$) lies above the price ($P$), but the price ($P$) remains above the Average Variable Cost ($AVC$).     * In this scenario, the firm still produces because it covers all variable costs and a portion of fixed costs.

• The Shutdown Point and the Point of Indifference     * The shutdown point occurs when the price ($P$) equals the Average Variable Cost ($AVC$).     * At this point, the firm is indifferent between producing or shutting down because the loss is exactly equal to the total fixed costs regardless of the decision.     * If the firm produces zero units, the loss equals fixed costs. If the firm produces at the shutdown point, the loss still equals fixed costs because revenue only covers variable costs.     * Most firms choose to shut down at this point to avoid further uncertainty.

• Short Run Supply Curve Derivation     * The individual firm's supply curve is derived from the upward-sloping portion of the Marginal Cost ($MC$) curve that lies above the Average Variable Cost ($AVC$) curve.

Derivation of the Long Run Market Supply Curve

• Long Run Characteristics     * In the long run, all factors of production are variable; therefore, there is no distinction between fixed and variable costs. Firms only face an Average Cost ($AC$) curve.     * The long run is characterized by the freedom of entry and exit for firms.

• Market Dynamics: Increase in Demand (Apple Industry Example)     * Phase 1: Initial Shift: If consumer preference for a product (e.g., apples) increases, the market demand curve shifts to the right.     * Phase 2: Price Increase and Economic Profit: The shift in demand increases the market equilibrium price. For the individual firm, this higher price ($P$) now lies above the $AC$ curve, resulting in economic profit.     * Phase 3: Market Signal and Entry: The presence of economic profit serves as a signal for new firms to enter the industry.     * Phase 4: Supply Shift: As new firms enter, the industry supply curve shifts to the right.     * Phase 5: Return to Normal Profit: The increase in supply drives the market price back down until it is tangent to the $AC$ curve. At this point, firms return to making only a normal profit.

• Market Dynamics: Decrease in Demand     * Phase 1: Demand Shift: A decrease in demand shifts the demand curve to the left.     * Phase 2: Price Drop and Loss: The market price falls below the $AC$ curve, causing firms to incur losses.     * Phase 3: Exit: Losses signal firms to leave the industry.     * Phase 4: Supply Shift: As firms exit, the industry supply curve shifts to the left, raising the price.     * Phase 5: Stabilization: The price continues to rise until it returns to the original equilibrium where firms earn a normal profit.

Constant Cost Industries and the Horizontal Supply Curve

• Definition of Constant Cost Industry     * A constant cost industry is one where the entry or exit of firms does not change the cost curves of the individual firms. There are no additional costs for resources or production factors as the industry expands or contracts.

• The Long Run Supply (LRS) Curve     * In a constant cost industry, the long run supply curve is horizontal (perfectly elastic).     * This implies that regardless of how demand fluctuates, the industry will always return to the same equilibrium price in the long run, ensuring firms only make normal profits.     * Quantities may increase or decrease significantly, but the long-run price remains constant.

Efficiency in Perfect Competition: Productive vs. Allocative

• Allocative Efficiency     * Definition: Producing the specific combination of goods and services most highly valued by society.     * Criteria: Allocative efficiency is achieved when Price equals Marginal Cost ($P = MC$).     * Application: Perfectly competitive firms are always allocatively efficient because they produce where $MR = MC$, and since $P = MR$ in perfect competition, it follows that $P = MC$.

• Productive Efficiency     * Definition: Producing goods at the lowest possible cost.     * Criteria: Productive efficiency is achieved when the firm produces at the minimum point of the Average Total Cost curve ($P = \min(ATC)$).     * Short Run vs. Long Run:         * In the short run, a firm is only productively efficient if it happens to be making a normal profit. If it is making an economic profit or a loss, it is not producing at the minimum of the $ATC$.         * In the long run, perfectly competitive firms are always productively efficient because the market forces of entry and exit force the price to the minimum of the $AC$ curve (normal profit).

Economic Welfare and Surplus Maximization

• Consumer Surplus     * The area between the demand curve and the equilibrium price point.

• Producer Surplus     * The area between the equilibrium price point and the supply curve.

• Welfare Maximization in Perfect Competition     * Economic welfare (the sum of consumer and producer surplus) is maximized in the long run under perfect competition.     * There is no deadweight loss because the industry produces at the lowest possible cost and provides exactly what society wants.

• Comparison with Monopolies     * Monopolies often charge higher prices and produce lower quantities than perfectly competitive industries.     * This results in smaller consumer and producer surpluses and the creation of a deadweight loss.     * Examples of competitive pricing include vegetable markets and taxis (compared to Ubers, which may have different pricing models).

Questions & Discussion

• Question on Inflation: How does inflation account for these price changes?     * Response: This analysis uses the ceteris paribus assumption (all other things being equal). It looks at one variable at a time without taking inflation into account. In advanced economics, factors like inflation and international trade are added to explain why market prices are not truly constant.

• Question on Market vs. Firm Equilibrium: Is the supply curve the same as the price?     * Response: No, they are distinct. In the industry (market), the long run supply curve is horizontal in a constant cost environment. The firm's equilibrium is determined by where its horizontal demand curve (price) intersects its marginal cost curve.

• Clarification on Shift Mechanics: Why show fluctuations if we always go back to normal profit?     * Response: If the supply curve does not shift enough after a demand increase, firms still make economic profit, attracting even more firms. If supply shifts too much (overshooting), firms incur losses, causing some to leave. These fluctuations continue until the industry stabilizes exactly at the normal profit level.