# 9.3: Perfect Competition in the Long Run

Learning Objectives

1. Distinguish between economic profit and accounting profit.
2. Explain why in long-run equilibrium in a perfectly competitive industry firms will earn zero economic profit.
3. Describe the three possible effects on the costs of the factors of production that expansion or contraction of a perfectly competitive industry may have and illustrate the resulting long-run industry supply curve in each case.
4. Explain why under perfection competition output prices will change by less than the change in production cost in the short run, but by the full amount of the change in production cost in the long run.
5. Explain the effect of a change in fixed cost on price and output in the short run and in the long run under perfect competition.

In the long run, a firm is free to adjust all of its inputs. New firms can enter any market; existing firms can leave their markets. We shall see in this section that the model of perfect competition predicts that, at a long-run equilibrium, production takes place at the lowest possible cost per unit and that all economic profits and losses are eliminated.

## Economic Profit and Economic Loss

Economic profits and losses play a crucial role in the model of perfect competition. The existence of economic profits in a particular industry attracts new firms to the industry in the long run. As new firms enter, the supply curve shifts to the right, price falls, and profits fall. Firms continue to enter the industry until economic profits fall to zero. If firms in an industry are experiencing economic losses, some will leave. The supply curve shifts to the left, increasing price and reducing losses. Firms continue to leave until the remaining firms are no longer suffering losses—until economic profits are zero.

Before examining the mechanism through which entry and exit eliminate economic profits and losses, we shall examine an important key to understanding it: the difference between the accounting and economic concepts of profit and loss.

## Economic Versus Accounting Concepts of Profit and Loss

Economic profit equals total revenue minus total cost, where cost is measured in the economic sense as opportunity cost. An economic loss (negative economic profit) is incurred if total cost exceeds total revenue.

Accountants include only explicit costs in their computation of total cost. Explicit costs include charges that must be paid for factors of production such as labor and capital, together with an estimate of depreciation. Profit computed using only explicit costs is called accounting profit. It is the measure of profit firms typically report; firms pay taxes on their accounting profits, and a corporation reporting its profit for a particular period reports its accounting profits. To compute his accounting profits, Mr. Gortari, the radish farmer, would subtract explicit costs, such as charges for labor, equipment, and other supplies, from the revenue he receives.

Economists recognize costs in addition to the explicit costs listed by accountants. If Mr. Gortari were not growing radishes, he could be doing something else with the land and with his own efforts. Suppose the most valuable alternative use of his land would be to produce carrots, from which Mr. Gortari could earn $250 per month in accounting profits. The income he forgoes by not producing carrots is an opportunity cost of producing radishes. This cost is not explicit; the return Mr. Gortari could get from producing carrots will not appear on a conventional accounting statement of his accounting profit. A cost that is included in the economic concept of opportunity cost, but that is not an explicit cost, is called an implicit cost. ## The Long Run and Zero Economic Profits Given our definition of economic profits, we can easily see why, in perfect competition, they must always equal zero in the long run. Suppose there are two industries in the economy, and that firms in Industry A are earning economic profits. By definition, firms in Industry A are earning a return greater than the return available in Industry B. That means that firms in Industry B are earning less than they could in Industry A. Firms in Industry B are experiencing economic losses. Given easy entry and exit, some firms in Industry B will leave it and enter Industry A to earn the greater profits available there. As they do so, the supply curve in Industry B will shift to the left, increasing prices and profits there. As former Industry B firms enter Industry A, the supply curve in Industry A will shift to the right, lowering profits in A. The process of firms leaving Industry B and entering A will continue until firms in both industries are earning zero economic profit. That suggests an important long-run result: Economic profits in a system of perfectly competitive markets will, in the long run, be driven to zero in all industries. ## Eliminating Economic Profit: The Role of Entry The process through which entry will eliminate economic profits in the long run is illustrated in Figure 9.14 “Eliminating Economic Profits in the Long Run”, which is based on the situation presented in Figure 9.7 “Applying the Marginal Decision Rule”. The price of radishes is$0.40 per pound. Mr. Gortari’s average total cost at an output of 6,700 pounds of radishes per month is $0.26 per pound. Profit per unit is$0.14 ($0.40 −$0.26). Mr. Gortari thus earns a profit of $938 per month (=$0.14 × 6,700).

Figure 9.14 Eliminating Economic Profits in the Long Run

If firms in an industry are making an economic profit, entry will occur in the long run. In Panel (b), a single firm’s profit is shown by the shaded area. Entry continues until firms in the industry are operating at the lowest point on their respective average total cost curves, and economic profits fall to zero.

Profits in the radish industry attract entry in the long run. Panel (a) of Figure 9.14 “Eliminating Economic Profits in the Long Run” shows that as firms enter, the supply curve shifts to the right and the price of radishes falls. New firms enter as long as there are economic profits to be made—as long as price exceeds ATC in Panel (b). As price falls, marginal revenue falls to MR2 and the firm reduces the quantity it supplies, moving along the marginal cost (MC) curve to the lowest point on the ATC curve, at \$0.22 per pound and an output of 5,000 pounds per month. Although the output of individual firms falls in response to falling prices, there are now more firms, so industry output rises to 13 million pounds per month in Panel (a).

## Eliminating Losses: The Role of Exit

Just as entry eliminates economic profits in the long run, exit eliminates economic losses. In Figure 9.15 “Eliminating Economic Losses in the Long Run”, Panel (a) shows the case of an industry in which the market price P1 is below ATC. In Panel (b), at price P1 a single firm produces a quantity q1, assuming it is at least covering its average variable cost. The firm’s losses are shown by the shaded rectangle bounded by its average total cost C1 and price P1 and by output q1.

Because firms in the industry are losing money, some will exit. The supply curve in Panel (a) shifts to the left, and it continues shifting as long as firms are suffering losses. Eventually the supply curve shifts all the way to S2, price rises to P2, and economic profits return to zero.

Figure 9.15 Eliminating Economic Losses in the Long Run

Panel (b) shows that at the initial price P1, firms in the industry cannot cover average total cost (MR1 is below ATC). That induces some firms to leave the industry, shifting the supply curve in Panel (a) to S2, reducing industry output to Q2 and raising price to P2. At that price (MR2), firms earn zero economic profit, and exit from the industry ceases. Panel (b) shows that the firm increases output from q1 to q2; total output in the market falls in Panel (a) because there are fewer firms. Notice that in Panel (a) quantity is designated by uppercase Q, while in Panel (b) quantity is designated by lowercase q. This convention is used throughout the text to distinguish between the quantity supplied in the market (Q) and the quantity supplied by a typical firm (q).

## Entry, Exit, and Production Costs

In our examination of entry and exit in response to economic profit or loss in a perfectly competitive industry, we assumed that the ATC curve of a single firm does not shift as new firms enter or existing firms leave the industry. That is the case when expansion or contraction does not affect prices for the factors of production used by firms in the industry. When expansion of the industry does not affect the prices of factors of production, it is a constant-cost industry. In some cases, however, the entry of new firms may affect input prices.

As new firms enter, they add to the demand for the factors of production used by the industry. If the industry is a significant user of those factors, the increase in demand could push up the market price of factors of production for all firms in the industry. If that occurs, then entry into an industry will boost average costs at the same time as it puts downward pressure on price. Long-run equilibrium will still occur at a zero level of economic profit and with firms operating on the lowest point on the ATC curve, but that cost curve will be somewhat higher than before entry occurred. Suppose, for example, that an increase in demand for new houses drives prices higher and induces entry. That will increase the demand for workers in the construction industry and is likely to result in higher wages in the industry, driving up costs.

An industry in which the entry of new firms bids up the prices of factors of production and thus increases production costs is called an increasing-cost industry. As such an industry expands in the long run, its price will rise.

Some industries may experience reductions in input prices as they expand with the entry of new firms. That may occur because firms supplying the industry experience economies of scale as they increase production, thus driving input prices down. Expansion may also induce technological changes that lower input costs. That is clearly the case of the computer industry, which has enjoyed falling input costs as it has expanded. An industry in which production costs fall as firms enter in the long run is a decreasing-cost industry.

Just as industries may expand with the entry of new firms, they may contract with the exit of existing firms. In a constant-cost industry, exit will not affect the input prices of remaining firms. In an increasing-cost industry, exit will reduce the input prices of remaining firms. And, in a decreasing-cost industry, input prices may rise with the exit of existing firms.

The behavior of production costs as firms in an industry expand or reduce their output has important implications for the long-run industry supply curve, a curve that relates the price of a good or service to the quantity produced after all long-run adjustments to a price change have been completed. Every point on a long-run supply curve therefore shows a price and quantity supplied at which firms in the industry are earning zero economic profit. Unlike the short-run market supply curve, the long-run industry supply curve does not hold factor costs and the number of firms unchanged.

Figure 9.16 “Long-Run Supply Curves in Perfect Competition” shows three long-run industry supply curves. In Panel (a), SCC is a long-run supply curve for a constant-cost industry. It is horizontal. Neither expansion nor contraction by itself affects market price. In Panel (b), SIC is a long-run supply curve for an increasing-cost industry. It rises as the industry expands. In Panel (c), SDC is a long-run supply curve for a decreasing-cost industry. Its downward slope suggests a falling price as the industry expands.

Figure 9.16 Long-Run Supply Curves in Perfect Competition

The long-run supply curve for a constant-cost, perfectly competitive industry is a horizontal line, SCC, shown in Panel (a). The long-run curve for an increasing-cost industry is an upward-sloping curve, SIC, as in Panel (b). The downward-sloping long-run supply curve, SDC, for a decreasing cost industry is given in Panel (c).