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# Lecture # 16 Monopoly Lecturer: Martin Paredes - PowerPoint PPT Presentation

Lecture # 16 Monopoly Lecturer: Martin Paredes. Outline. The Monopolist's Profit Maximization Problem The Profit Maximization Condition Equilibrium The Inverse Elasticity Pricing Rule The Welfare Economics of Monopoly. Monopoly Market.

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Monopoly

Lecturer: Martin Paredes

• The Monopolist's Profit Maximization Problem

• The Profit Maximization Condition

• Equilibrium

• The Inverse Elasticity Pricing Rule

• The Welfare Economics of Monopoly

Definition: A monopoly market consists of a single seller facing many buyers.

Assumption: There are barriers to entry.

• The monopolist's objective is to maximise profits:

Max (Q) = TR(Q) – TC(Q) = P(Q)· Q – C(Q) Q

where P(Q) is the (inverse) market demand curve.

• Profit maximizing condition for a monopolist:

dTR(Q) = dTC(Q) …or… MR(Q) = MC(Q) dQ dQ

• In other words, the monopolist sets output so that the marginal profit of additional production is just zero.

• Recall that a perfect competitor sets P = MC, because MR = P.

• This is not true for the monopolist because the demand it faces is NOT flat.

• As a result, MR < P

• Since TR(Q) = P(Q) · Q, then:

dTR(Q) = MR(Q) = P(Q) + dP(Q) · Q dQ dQ

• In perfect competition, demand is flat, meaning dP(Q)/dQ = 0, so MR = P.

• For a monopoly, demand is downward-sloping, meaning dP(Q)/dQ < 0, so MR < P.

Example: Marginal Revenue

Price

Price

Competitive firm Monopolist

Demand facing firm

Demand facing firm

P0

P0

C

P1

B

A

B

A

q q+1

Firm output

Q0

Q0+1

Firm output

Example: Marginal Revenue Curve and Demand

The MR curvelies below the demand curve.

P(Q0)

P(Q), the (inverse) demand curve

Quantity

Q0

Example: Marginal Revenue Curve and Demand

The MR curvelies below the demand curve.

P(Q0)

P(Q), the (inverse) demand curve

MR(Q0)

MR(Q), the marginal revenue curve

Quantity

Q0

Example: Marginal revenue for linear demands

• Suppose demand is linear: P(Q) = a – bQ

• Total revenue is TR = Q*P(Q) = aQ – bQ2

• Marginal revenue is: MR = dTR = a – 2bQ dQ

• So, for linear demands, marginal revenue has twice the slope of demand.

Definition: An agent has market power if she can affect the price that prevails in the market through her own actions.

• Sometimes this is thought of as the degree to which a firm can raise price above marginal cost.

• In the short run, the monopolist shuts down if the profit-maximising price does not cover AVC (or average non-sunk costs).

• In the long run, the monopolist shuts down if the profit-maximising price does not cover AC.

Example: Profit maximisation

• Suppose: P(Q) = 100 – Q

TC(Q) = 100 + 20Q + Q2

• Marginal revenue is: MR = dTR = 100 – 2Q dQ

• Marginal cost is: MC = dTC = 20 + 2Q dQ

• MR = MC ==> 100 – 2Q = 20 + 2Q ==> Q* = 20 P* = 80

Example: Profit maximisation

• In equilibrium Q* = 20 P* = 80

• Observe that: AVC = 20 + Q* = 40 AC = 100 + 20 + Q* = 45 Q*

• Hence, P* > AVC and P* > AC

Example: Positive Profits for Monopolist

100

Demand curve

100

Quantity

Example: Positive Profits for Monopolist

100

MR

Demand curve

50

100

Quantity

Example: Positive Profits for Monopolist

MC

100

MR

20

Demand curve

50

100

Quantity

Example: Positive Profits for Monopolist

MC

100

MR

20

Demand curve

20

50

100

Quantity

Example: Positive Profits for Monopolist

MC

100

E

80

MR

20

Demand curve

20

50

100

Quantity

Example: Positive Profits for Monopolist

MC

AVC

100

E

80

MR

20

Demand curve

20

50

100

Quantity

Example: Positive Profits for Monopolist

MC

AVC

100

E

80

AC

MR

20

Demand curve

20

50

100

Quantity

Example: Positive Profits for Monopolist

MC

AVC

100

E

80

: Profits

AC

MR

20

Demand curve

20

50

100

Quantity

Notes:

A monopolist has less incentive to increase output than the perfect competitor: for the monopolist, an increase in output causes a reduction in its price.

Profits can remain positive in the long run because of the assumption that there are barriers to entry.

Notes:

• A monopolist does not have a supply curve: because price is determined endogenously by the demand:

• The monopolist picks a preferred point on the demand curve.

• Alternative view: the monopolist chooses output to maximize profits subject to the constraint that price be determined by the demand curve.

• We can rewrite the MR curve as follows:

MR = P + dP · Q dQ

= P + dP · Q · P dQ P

= P 1 + dP · Q dQ P

= P 1 + 1 

( )

( )

• Given that  is the price elasticity of demand:

• When demand is elastic ( < -1), then the marginal revenue is positive (MR > 0).

• When demand is unit elastic ( = -1), then the marginal revenue is zero (MR= 0).

• When demand is inelastic ( > -1), then the marginal revenue is negative (MR < 0).

Example: Elastic Region of Linear Demand Curve

a

Demand

a/b

Quantity

Example: Elastic Region of Linear Demand Curve

a

MR

Demand

a/2b a/b

Quantity

Example: Elastic Region of Linear Demand Curve

a

Elastic region ( < -1), MR > 0

MR

Demand

a/2b a/b

Quantity

Example: Elastic Region of Linear Demand Curve

a

Elastic region ( < -1), MR > 0

Inelastic region (0>>-1), MR<0

MR

Demand

a/2b a/b

Quantity

Example: Elastic Region of Linear Demand Curve

a

Elastic region ( < -1), MR > 0

Unit elastic (=-1), MR=0

Inelastic region (0>>-1), MR<0

MR

Demand

a/2b a/b

Quantity

• A monopolist will only operate on the elastic region of the market demand curve

• Note: As demand becomes more elastic at each point, marginal revenue approaches price.

• The monopolist will produce at MR = MC, but we also found that:

MR = P 1 + 1 

• Then: P 1 + 1 = MC 

or: P – MC = –1 P 

( )

( )

Definition: The Lerner Index of market power is the price-cost margin, (P*-MC)/P*.

• It measures the monopolist's ability to price above marginal cost, which in turn depends on the elasticity of demand.

• The Lerner index ranges between 0 (for the competitive firm) and 1 (for a monopolist facing a unit elastic demand).

• A monopoly equilibrium entails a dead-weight loss.

• For the following analysis, suppose the supply curve in perfect competition is equal to the marginal cost curve of the monopolist.

Example: Welfare Effects of Perfect Competition

Supply

PC

Demand

QC

MR

Example: Welfare Effects of Perfect Competition

Supply

: Consumer Surplus

PC

: Producer Surplus

Demand

QC

MR

Example: Welfare Effects of Monopoly

MC

PC

Demand

QC

MR

Example: Welfare Effects of Monopoly

MC

PM

PC

Demand

QM

QC

MR

Example: Welfare Effects of Monopoly

MC

PM

: Consumer Surplus

PC

Demand

QM

QC

MR

Example: Welfare Effects of Monopoly

MC

PM

: Consumer Surplus

: Producer Surplus

PC

Demand

QM

QC

MR

Example: Welfare Effects of Monopoly

MC

PM

: Consumer Surplus

: Producer Surplus

PC

Demand

QM

QC

MR

A monopoly market consists of a single seller facing many buyers (utilities, postal services).

A monopolist's profit maximization condition is to set marginal revenue equal to marginal cost.

Marginal revenue generally is lower than price. How much less depends on the elasticity of demand.

A monopolist never produces on the inelastic portion of demand since, in the inelastic region, raising price and reducing quantity make total revenues rise and total costs fall!

The Lerner Index is a measure of market power, often used in antitrust analysis.

A monopoly equilibrium entails a dead-weight loss.