Perfect competition
In economics, perfect competition occurs in markets in which no participant has market power. Because the conditions for perfect competition are strict, there are few if any perfectly competitive markets. Nonetheless, the concept of perfect competition can serve as a useful benchmark against which to measure real life, imperfectly competitive markets
Generally, a perfectly competitive market exists when every participant is a "price taker," and no participant influences the price of the product it buys or sells. Specific characteristics may include:
§ Infinite Buyers/Infinite Sellers – Infinite consumers with the willingness and ability to buy the product at a certain price, Infinite producers with the willingness and ability to supply the product at a certain price.
§ Zero Entry/Exit Barriers – It is relatively easy to enter or exit as a business in a perfectly competitive market.
§ Perfect Information - Prices and quality of products are assumed to be known to all consumers and producers.
§ Transactions are Costless - Buyers and sellers incur no costs in making an exchange [Perfect mobility].
§ Firms Aim to Maximize Profits - Firms aim to sell where marginal costs meet marginal revenue, where they generate the most profit.
§ Homogeneous Products – The characteristics of any given market good or service do not vary across suppliers.
Some subset of these conditions is presented in most textbooks as defining perfect competition. More advanced textbooks try to reconcile these conditions with the definition of perfect competition as equilibrium price taking; that is whether or not firms treat price as a parameter or a choice variable. It should be noted that a general rigorous proof that the above conditions indeed suffice to guarantee price taking is still lacking (Kreps 1990, p. 265).
In the short term, perfectly-competitive markets are not productively inefficient as output will not occur where marginal cost is equal to average cost, but allocatively efficient, as output will always occur where marginal cost is equal to marginal revenue, and therefore where marginal cost equals average revenue. In the long term, such markets are both allocatively and productively efficient.
Under perfect competition, any profit-maximizing producer faces a market price equal to its marginal cost. This implies that a factor's price equals the factor's marginal revenue product. This allows for derivation of the supply curve on which the neoclassical approach is based. (This is also the reason why "a monopoly does not have a supply curve.") The abandonment of price taking creates considerable difficulties to the demonstration of existence of a general equilibrium except under other, very specific conditions such as that of monopolistic competition .
n a perfectly competitive market, a firm's demand curve is perfectly elastic.
As mentioned above, the perfect competition model, if interpreted as applying also to short-period or very-short-period behaviour, is approximated only by markets of homogeneous products produced and purchased by very many sellers and buyers, usually organized markets for agricultural products or raw materials. In real-world markets, assumptions such as perfect information cannot be verified and are only approximated in organized double-auction markets where most agents wait and observe the behaviour of prices before deciding to exchange (but in the long-period interpretation perfect information is not necessary, the analysis only aims at determining the average around which market prices gravitate, and for gravitation to operate one does not need perfect information).
In the absence of externalities and public goods, perfectly competitive equilibria are Pareto-efficient, i.e. no improvement in the utility of a consumer is possible without a worsening of the utility of some other consumer. This is called the First Theorem of Welfare Economics. The basic reason is that no productive factor with a non-zero marginal product is left unutilized, and the units of each factor are so allocated as to yield the same indirect marginal utility in all uses, a basic efficiency condition (if this indirect marginal utility were higher in one use than in other ones, a Pareto improvement could be achieved by transferring a small amount of the factor to the use where it yields a higher marginal utility).
A simple proof assuming differentiable utility functions and production functions is the following. Let wj be the 'price' (the rental) of a certain factor j, let MPj1 and MPj2 be its marginal product in the production of goods 1 and 2, and let p1 and p2 be these goods' prices. In equilibrium these prices must equal the respective marginal costs MC1 and MC2; remember that marginal cost equals factor 'price' divided by factor marginal productivity (because increasing the production of good i by one very small unit through increase of the employment of factor j requires increasing the factor employment by 1/MPji and thus increasing the cost by wj/MPji, and through the condition of cost minimization that marginal products must be proportional to factor 'prices' it can be shown that the cost increase is the same if the output increase is obtained by optimally varying all factors). Optimal factor employment by a price-taking firm requires equality of factor rental and factor marginal revenue product, wj=piMPji, so we obtain p1=MC1=wj/MPj1, p2=MCj2=wj/MPj2.
Now choose any consumer purchasing both goods, and measure his utility in such units that in equilibrium his marginal utility of money (the increase in utility due to the last unit of money spent on each good), MU1/p1=MU2/p2, is 1. Then p1=MU1, p2=MU2. The indirect marginal utility of the factor is the increase in the utility of our consumer achieved by an increase in the employment of the factor by one (very small) unit; this increase in utility through allocating the small increase in factor utilization to good 1 is MPj1MU1=MPj1p1=wj, and through allocating it to good 2 it is MPj2MU2=MPj2p2=wj again. With our choice of units the marginal utility of the amount of the factor consumed directly by the optimizing consumer is again w, so the amount supplied of the factor too satisfies the condition of optimal allocation.
Monopoly violates this optimal allocation condition, because in a monopolized industry market price is above marginal cost, and this means that factors are underutilized in the monopolized industry, they have a higher indirect marginal utility than in their uses in competitive industries. Of course this theorem is considered irrelevant by economists who do not believe that general equilibrium theory correctly predicts the functioning of market economies; but it is given great importance by neoclassical economists and it is the theoretical reason given by them for combating monopolies and for antitrust legislation.
Profit
In contrast to a monopoly or oligopoly, it is impossible for a firm in perfect competition to earn economic profit in the long run, which is to say that a firm cannot make any more money than is necessary to cover its economic costs. In order not to misinterpret this zero-long-run-profits thesis, it must be remembered that the term 'profit' is also used in other ways. Neoclassical theory defines profit as what is left of revenue after all costs have been subtracted, including normal interest on capital plus the normal excess over it required to cover risk, and normal salary for managerial activity. Classical economists on the contrary defined profit as what is left after subtracting costs except interest and risk coverage; thus, if one leaves aside risk coverage for simplicity, the neoclassical zero-long-run-profit thesis would be re-expressed in classical parlance as profits coinciding with interest in the long period, i.e. the rate of profit tending to coincide with the rate of interest. Profits in the classical meaning do not tend to disappear in the long period but tend to normal profit. With this terminology, if a firm is earning abnormal profit in the short term, this will act as a trigger for other firms to enter the market. They will compete with the first firm, driving the market price down until all firms are earning normal profit only.
In contrast to a monopoly or oligopoly, it is impossible for a firm in perfect competition to earn economic profit in the long run, which is to say that a firm cannot make any more money than is necessary to cover its economic costs. In order not to misinterpret this zero-long-run-profits thesis, it must be remembered that the term 'profit' is also used in other ways. Neoclassical theory defines profit as what is left of revenue after all costs have been subtracted, including normal interest on capital plus the normal excess over it required to cover risk, and normal salary for managerial activity. Classical economists on the contrary defined profit as what is left after subtracting costs except interest and risk coverage; thus, if one leaves aside risk coverage for simplicity, the neoclassical zero-long-run-profit thesis would be re-expressed in classical parlance as profits coinciding with interest in the long period, i.e. the rate of profit tending to coincide with the rate of interest. Profits in the classical meaning do not tend to disappear in the long period but tend to normal profit. With this terminology, if a firm is earning abnormal profit in the short term, this will act as a trigger for other firms to enter the market. They will compete with the first firm, driving the market price down until all firms are earning normal profit only.
It is important to note that perfect competition is a sufficient condition for allocative and productive efficiency, but it is not a necessary condition. Laboratory experiments in which participants have significant price setting power and little or no information about their counterparts consistently produce efficient results given the proper trading institutions (Smith, 1987, p. 245).
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