1. Chapter 9 Perfect Competition In A Single Market

2. Objectives What are perfectly competitive markets
How prices are determined in a perfectly competitive market
Why entry and exit of firms occur and its effects
Welfare consequences

3. Supply Response
The effects of changes in demand depend on the time period considered
It takes time for suppliers to respond
Time frames
Very short run – quantity supplied is fixed (market period)
Short run – existing firms can respond but no new entry
Long run – existing firms can respond and new firms can enter.

4. Very Short Run S
Price
Given some demand, D, the equilibrium price, P1, is where demand intersects supply. P1 D
Quantity per week Q*

5. Pricing In The Very Short Run
If the demand curve increases there is excess demand at P1. S
Price P2
To ration the quantity available, price must rise to P2. P1 D’ D
Quantity per week Q*

6. Short-Run Supply
Assume that the number of firms in the market is fixed: no new entry or exit.
Existing firms can respond to changes in demand by increasing or decreasing their quantity supplied.

7. Short-Run Supply Firm A Firm B Market Price Price Price S SA SB P1 q1A
q1B Q
Output

8. Short-Run Price Determination
SMC S
SAC P1 d D Q Q1 Q Q
Typical Firm
Typical Person
The Market

9. Short-Run Price Determination
SMC S
SAC P1 P1 d D q1 Q Q1 Q q1 Q
Typical Firm
Typical Person
The Market

10. Short-Run Price Determination
Price serves two functions
It acts as a signal to producers: given some price they maximize profits where P = SMC
It rations demand. Given some price consumers buy the amount that will maximize their utility
Note that both producers and consumers are content with the outcome.

11. Short-Run Price Determination: What Happens When Demand Changes
SMC S P2
SAC P1 P1 D’ d’ d D q1 q2 Q Q1 Q2 Q q1 q2 Q
Typical Firm
Typical Person
The Market

12. Shifts in Supply and Demand Curves
Demand shifts when:
Income increases and the good is normal
Income increases and the good is inferior
The price of a substitute rises
The price of a complement falls
Preferences for a good change

13. Shifts in Supply and Demand Curves
Reasons for a shift in supply:
Input prices falls
Technology improves

14. Shifts in Supply Price Price S’ S’ S S P’ P’ P P D D Q’ Q
Quantity per week Q’ Q
Quantity per week
The change in price and quantity depend on the elasticity of demand

15. Shifts in Demand S Price Price S P’ P’ P P D’ D’ D D Q Q’
Quantity per week Q Q’
Quantity per week
The change in price and quantity depend on the elasticity of supply

16. LR or SR equilibrium?
Price
Price
ATC S MC D π1 pe
q1e Q
Market
FIRM 1

17. The Long Run In the long run supply adjusts through
Firms adjust all input.
Firms can enter or exit the industry.
How does the LR Supply look like?
Changes in price cause changes in quantity supplied
We change price by shifting demand
We examine the quantity produced by the industry after both adjustments take place and an (LR) equilibrium is reached

18. The Long Run Equilibrium conditions
Profit Maximization
Each firm maximizes profits by producing q where P = MC.
Market clearing:
Price, P, equates QS and QD
Entry and Exit
no further changes in the number of firms, n, since firms have entered or exited the industry
There are no extra costs to enter or exit the industry.
If there are economic profits in the short run, new firms will enter. This will increase supply, push down the market price and reduce profits.
If there are economic losses in the short run, firms will exit. This will decrease supply, push the price up and eliminate the economic losses.
P=min ATC

19. Long Run Supply In the short run The long run supply can be
Supply is upward sloping
The long run supply can be
Flat
Upward sloping
Downward sloping
The shape of the LR supply will depend on how entry/exit affects the costs of production

20. Dynamic Changes in Market Equilibria
Constant-cost industries
Entry of new firms has no impact on the cost of prodution
The LRAC is unaffected
Flat long-run supply curve

21. Constant-cost industries
LRAC
Price
Cost D2
Long-run
supply curve
SRMC
SRAC D1 S1 S2 b pb a pa
Quantity
Quantity
With constant costs, the long-run response to an increase in demand re-establishes the original price of pa.

22. Increasing-cost industries
As new firms enter
Cost of inputs increase
LRAC curves – shift up
Pecuniary externality
Action of one agent
Upward sloping long-run supply curve

23. Increasing-cost industries
Price
Cost D2
LRAC1
LRAC2
Long-run
supply curve D1 S1 S3 b pb c pc pa a
Quantity
Quantity
With increasing costs, the long-run response results in a higher price

24. Decreasing-cost industries
Downward sloping long-run supply curve
As new firms enter
Decrease costs of inputs
Economies of scale in making inputs
Subsidiary services develop
LRAC curves – shift down

25. Decreasing-cost industries
Price
Cost D2
LRAC1
Long-run
supply curve D1 S1
LRAC2 b S2 pa c a pc
Quantity
Quantity
With decreasing costs, the long-run response results in a lower price.

26. Consumer and Producer Surplus
Consumer surplus is the extra value individuals receive from consuming a good over what they pay for it. What people are willing to pay for the right to consume a good at its current market price.
Producer surplus is the extra value producers receive for a good in excess of the opportunity costs they incur by producing it. What all producers would pay for the right to sell a good at its current market price.

27. Consumer and Producer Surplus
Total value to consumers from buying Q* units.
Price A S
Total expenditure by consumers. P*
Consumer Surplus D B
Quantity
per period Q*

28. Consumer and Producer Surplus
Total revenue earned by firms
Price
Minimum amount necessary to produce Q* units. A S
Producer surplus P* D B
Quantity
per period Q*

29. Consumer and Producer Surplus
In the short run, producer surplus reflects both actual profits in the short run and all fixed costs.
It is a measure of how much firms gain by participating in the market rather than shutting down.
In the long run, producer surplus measures all of the increased payments relative to the situation in which the industry produces no output.
Ricardian Rent – long run profits earned by owners of low-cost firms. These rents may be capitalized into the prices of the resources.

30. Economic Efficiency In what sense is a competitive market efficient?
Economically efficient allocation of resources is one in which the sum of consumer and producer surplus is maximized. It reflects the best use of societies resources.
At market equilibrium there are no more mutually beneficial exchanges.

31. Economic Efficiency Suppose only Q1 units are produced.
Price
There is a loss in total surplus. A S P* D B
Quantity
per period Q1 Q*

32. Economic Efficiency
At Q1, consumers are willing to pay P1 and producers are willing to accept P2: mutually beneficial exchange possible.
Price A S P1 P* P2 D B
Quantity
per period Q1 Q*

33. Some Applications: Tax Incidence
Tax incidence considers the burden of a tax after considering all market reactions to it.
Suppose a fixed per unit tax is imposed on all firms. Although the firms are legally obligated to pay the tax to the government, who actually end up paying?

34. Tax Incidence in the Short Run: Constant Costs
(a) Typical Firm
(b) The Market
Price
Price
Consumer pays S MC AC P3 P1 P2
Tax
Firm keeps after tax D D’ q2 q1 Q2 Q1
Output
Quantity
per week

35. Tax Incidence in the Short Run: Constant Costs
So in the short run, the tax is borne by consumers and producers:
P3 > P1 > P2 and P3 – P2 = tax
What will happen in the long run?
Since P2 < AC, there are economic losses. Some firms will exit, which will reduce supply and cause the price to rise. Exit will continue until the price has risen by the full amount of the tax.

36. Tax Incidence in the Long Run: Constant Costs
(a) Typical Firm
(b) The Market
Price
Price S’ S MC P4 AC P3
Tax P1 P2
Tax D D’ Q3 q2 q1 Q2 Q1
Output
Quantity
per week

37. Long Run Incidence: Increasing Costs
Price S
P2 is the price retained by firms after paying tax. P3
TAX
REVENUE
CONSUMER
BURDEN
P3 is the full price paid by the consumer. P1
FIRM
BURDEN P2
Deadweight loss.
Tax D D’ Q2 Q1
Quantity
per week

38. Summary of Tax Incidence
In a constant cost industry the burden of the tax falls fully on consumers in the long run.
In an increasing cost industry, the burden of the tax is shared between consumers and producers.
The relative burden will depend on the elasticity of demand and supply.
If demand is relatively inelastic and/or supply elastic, demanders will pay a relatively larger share of the tax.
Since taxation reduces output compared to what normally would occur, there is a deadweight loss and a loss of efficiency.

39. Recap I
The short run supply curve, which represents the decisions of price taking firms is positively sloped since the firms’ marginal costs curves are positively sloped.
At the equilibrium price the quantity supplied is exactly equal to the quantity demanded.
The effects of shifts in supply and/or demand on price will depend on the shapes of both curves.
Economic profits will attract new firms and shift the supply curve outward. Economic loss will cause some firms to leave the industry and shift the supply curve inward. This will continue until economic profits are zero in the long run.

40. Recap II
The long run supply curve is horizontal when the entry of new firms has no effect on input prices. The long run supply curve is increasing if the entry of new firms causes input prices to rise.
As long as there are no market imperfections, the sum of producer and consumer surplus (welfare) is maximized under perfect competition.
In a constant cost industry the incidence of the tax will fall completely on the consumer in the long run. In an increasing cost industry the incidence of the tax will fall on both the consumer and the producer and will depend on the elasticity of demand and supply.
A tariff will lead to a transfer of surplus from consumers to produces and a welfare loss.