Thesis title: On the standards and types of market structure. urgent

(1) Market structure refers to the degree of monopoly and competition in the market. (2) Different levels of competition and monopoly in each market have formed different market structures, which are divided according to three standards. First, the market concentration of the industry. Market concentration refers to the degree of market control by large enterprises, expressed by market share. Usually, four concentration ratios and Herfindal-Hirschman index (HHl) are used to judge the concentration ratio of a market. Second, the entry restrictions of the industry. Access restrictions come from natural reasons and legislative reasons. Natural causes refer to resource control and economies of scale. If an enterprise controls the key resources of an industry, other enterprises cannot enter the industry without these resources. The legislative reason is that the law restricts the access of certain industries. This legislative restriction mainly takes three forms: one is franchising, the other is licensing system, and the third is patent system. Third, product differences. Product difference is the difference in quality, brand, form and packaging of the same product. Product differences lead to monopoly, and the greater the product differences, the higher the degree of monopoly. (3) According to the above three standards, the market structure can be divided into four types. First, perfect competition is a market structure in which competition is not hindered or interfered by any means. The conditions for forming this market are that there are many enterprises, and each enterprise is small in scale. The price is determined by the supply and demand of the whole market, and each enterprise cannot influence the market price by changing its own output. Second, monopoly competition is a market where monopoly and competition coexist, and it is a combination of monopoly and competition. The similarity between this market and perfect competition lies in the low market concentration and no entry restrictions. But the key difference is that there is no difference between perfectly competitive products and monopolistic competitive products. The small scale of enterprises and unrestricted access also ensure the existence of competition in this market. Third, oligopoly is a market with only a few large enterprises, and the key to forming this market is economies of scale. In this market, large enterprises have high concentration and strong control over the market, and can influence prices by changing output. And because each enterprise is large in scale, it is difficult for other enterprises to enter. Because it is not a monopoly, there is fierce competition among several oligarchs. Fourth, monopoly means that only one enterprise controls the supply of the whole market. The key condition of monopoly is entry restriction, which can come from natural reasons or legislation. In addition, another condition of monopoly is that there are no similar substitutes, and there are substitutes to compete with them.