LOS16 The firm and market structures
1. perfect competition, monopolistic competition, oligopoly, monopoly
Industry clothes toothpaste car electric power
2. perfect competition: price taker
Demand curve: horizontal
P=MR=MC=ATC perfectly elastic
The long-run equilibrium output: MR=MC=ATC economic profit=0
3.monoplistic competition
Demand curve: downward sloping highly elastic
Product innovation is a necessary and advertising expense are high
4. oligopoly
①Kinked demand curve model
An increase price will not be followed by its competitors, but a decrease in price will.
Maximizing price: the price which the kink is located. Where the kink is located is outside of the model.
②Cournot duopoly model
Two firms in the market
identical MC
each firm knows the quantity supplied by the other firm in the previous period and assumes that is what it will supply in the next period
P>MC
③Nash equilibrium model (prisoner’s dilemma)
The best choice for a firm depends on the actions (reactions) of other firms
A Nash equilibrium is reached when the choices of all firms are such that there is no other choice that makes any firm better off
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④Stackelberg dominant firm model
The market price is determined by the dominant firm, and the other competitive firms take this market price as given
CF decreases price (lower than P*), Q(cf) increases. P(df) follows. In the long run, CF decreases the price or exit the industry and increase the market share of dominant firm.
5. Monopoly
Price strategies: single price and price discrimination
When price discrimination isn’t possible, the monopoly will charge a single price.
Conditions:
•Downward-sloping demand curve
•At least two identifiable groups of customers with different price elasticities of demand
•Prevent trades between different groups
Deadweight loss: rent seeking when producers spend time and resources to try to acquire or establish a monopoly.
Natural monopoly
High fix cost, only one firm can exist
Average cost pricing
Marginal cost pricing
6. supply function
There is no well-defined supply function in monopolistic competition, oligopoly and monopoly markets.
7. the use and limitations of concentration measures in identifying market structures
N-firm concentration ratio: sum of the percentage market shares of the largest N firms in a market
Shortcomings: insensitive to mergers of two firms
Barriers to entry are not considered
Herfindahl-Hirschman Index(HHI): percentage squares
Shortcomings: Barriers to entry are not considered
If barriers to entry are low, even a firm with high market share may not have much pricing power. If they increase prices, new firms enter, the elasticity of demand for existing firms may be high.


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