Market Structure
What is Market Structure?
Market structure is how a market is organized: the number of firms, how differentiated their products are, how hard entry is, and how much firms set price.
Economists sort markets using four tests: the number of sellers, whether the product is identical or differentiated, how hard it is to enter, and how much control a firm has over price. Perfect competition has many firms selling an identical good with free entry, so every firm is a price taker; monopolistic competition keeps the many firms and the free entry but differentiates the product, giving each firm a little pricing room. Oligopoly has a few large firms behind real entry barriers, so each firm's best move depends on what its rivals do, while monopoly has one seller of a good with no close substitutes and blocked entry, which carries the most pricing power. Moving down that list, price rises further above marginal cost and output falls further below the efficient level. Structure is not the same as market power: structure describes a whole market, while market power describes one firm's ability to hold price above marginal cost.
Market Structure: a worked example
Take one city and apply the four tests twice. Its tap water comes from a single utility, no household can buy from a rival, and a second pipe network would cost more than the whole market is worth, so that is a monopoly with blocked entry and full pricing control. Its 40 coffee shops sell a similar but not identical product, anyone can lease a storefront and open another, and a shop charging $9 for a latte loses most but not all of its customers, so that is monopolistic competition. Same city, same buyers, two different structures, because the tests turn on entry and differentiation rather than on the size of the town.
The mistake students make with market structure
The name misleads students into filing monopolistic competition next to monopoly. It sits much closer to perfect competition: many firms, easy entry, and economic profit competed away to zero in the long run. The only difference from perfect competition is that products are differentiated, so the demand curve each firm faces slopes down slightly instead of lying flat. That small slope is the entire source of its pricing power.
Market Structure questions
What are the four market structures?
The four market structures are perfect competition, monopolistic competition, oligopoly and monopoly, listed from most competitive to least. They are ranked by the number of sellers, how differentiated the product is, and how hard it is for a new firm to enter.
What determines a market's structure?
A market's structure is determined by four features: the number of firms, whether the product is standardized or differentiated, the height of barriers to entry, and how much power a single firm has over price. Barriers to entry usually do the most work, because free entry is what erases economic profit in the long run.
Which market structure is the most efficient?
Perfect competition is the most efficient structure, because its long-run equilibrium puts price equal to marginal cost (allocative efficiency) and output at the minimum of average total cost (productive efficiency). Every other structure sets price above marginal cost, so trades that both sides would have gained from never happen and deadweight loss appears.
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