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Static Oligopoly Model
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n firms, each firm chooses an action once
choices are simultaneous
no scope for any firm to react to rivals choices or influence each other
each firm chooses its action to maximize its own payoff taking as given the choices it expects by other firms
choices are simultaneous
no scope for any firm to react to rivals choices or influence each other
each firm chooses its action to maximize its own payoff taking as given the choices it expects by other firms
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Cournot Model
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each firm chooses a quantity it offers for sale, a=q
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Bertrand
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each firm chooses a price at which its willing to sell any quantity, a=p
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Examples of Markets
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Cournot: oil or other commodity markets
Bertrand: differentiated products with constant marginal costs
Bertrand: differentiated products with constant marginal costs
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Nash Equilibrium
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A firm's payoff can depend on its action a and the vector of all other firms actions --> under differentiated products Bertrand competition
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Homogenous Products Cournot
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profits of any firm i depend only on its output q and the total of other firms outputs
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Non-Cooperative Nash Equilibrium
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A set of actions, one for each firm, such that for each firm i, taking as given the equilibrium choices of others, its own choice a is at least as good for it any other feasible choice
The action is the best response function of i to expected choices of others
The action is the best response function of i to expected choices of others
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Cournot Competition Linear Case
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firms sell homogenous products
price determined when total quantity by all firms is given to an auctioneer who sets market clearing price
we can see how price varies as a function of our own choice of q
each firm behaves as a monopolist on its own inverse residual demand -- residual demand depends on the given choices of other firms, which are correctly expected by each firm
price determined when total quantity by all firms is given to an auctioneer who sets market clearing price
we can see how price varies as a function of our own choice of q
each firm behaves as a monopolist on its own inverse residual demand -- residual demand depends on the given choices of other firms, which are correctly expected by each firm
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Best Response Function Cournot
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monopoly output minus 1/2 the output it expects of others, because increasing rivals output by Δ shifts i's residual demand left by Δ, so its MR shifts left by Δ/2. With constant MC, its optimal output decreases by Δ/2
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Duopoly Equilibrium
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simultaneously solving the two FOCs, which gives the cournot equilibrium outputs as functions of only the demand and cost parameters
firms output increases if its own marginal cost falls or if the rivals rises, and (a) effect is stronger than (b)
q=(a-2c1+c2)/3b
firms output increases if its own marginal cost falls or if the rivals rises, and (a) effect is stronger than (b)
q=(a-2c1+c2)/3b
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n symmetric firms
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if all have identical marginal costs
q=1/(n+1)*Qpc
Qc=n/(n+1)Qpc
Qpc=(a-c)/b
q=1/(n+1)*Qpc
Qc=n/(n+1)Qpc
Qpc=(a-c)/b
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Under Supply Socially
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cournot industry output is below the optimal level for society
any active firm has price above MC, so expanding its output would raise welfare
any active firm has price above MC, so expanding its output would raise welfare
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Over-Supply Privately
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industry output is above the optimal level for the industry
expansion by firm j harms any other firm i by depressing price which reduces i's revenue in proportion to i's output
expansion by firm j harms any other firm i by depressing price which reduces i's revenue in proportion to i's output
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Misallocation of production across firms if MCs differ
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equilibrium industry output could be produced at lower cost by shifting output from firms with higher MCs to firms with lower MCs
in cournot, firms with lower MCs do have higher ouputs, but higher MC firms still survive despite selling homogenous products, so industry cost could be reduced by shifting additional output away from them
in cournot, firms with lower MCs do have higher ouputs, but higher MC firms still survive despite selling homogenous products, so industry cost could be reduced by shifting additional output away from them