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Analysis of Competitive Markets
In this section, we examine the social welfare
implications of competitive markets.
The approach taken here (and not the only one
possible), is to use the devices of Producer and
Consumer Surplus.
The social welfare from the production and
consumption of a particular amount of a good is
assumed to be the sum of the producer and
consumer surplus.
Welfare economics
slide 1
Optimality of competitive markets
The principal claim is that social welfare (the sum of
producer and consumer surplus) is maximized at
the competitive price and quantity for a good.
A series of examples are worked to show that a
variety of policies and regulations, such as price
fixing, taxes, and subsidies, will, in general,
reduce social welfare from its maximum.
Welfare economics
slide 2
Key terms
Willingness to pay: The maximum amount a buyer
will pay for an amount of a good.
Consumer surplus: A buyer's willingness to pay
minus the amount actually paid.
Cost: The value of everything a seller must give up
to produce an amount of a good.
Producer surplus: The amount the seller receives for
the good minus the cost.
Welfare economics
slide 3
Consumer surplus can be measured using
the demand curve for a product.
P
Demand for tacos
P*
D
Q*
Welfare economics
Q
slide 4
When Q* is sold, willingness to pay is the
shaded area.
P
Demand for tacos
P*
D
Q*
Welfare economics
Q
slide 5
When Q* is sold at a price P*, consumers pay P*
times Q*. Click to see the cost to consumers.
Click again to see the shaded area that is
consumer surplus.
P
Consumer surplus
P*
Demand for tacos
Cost to
consumers
D
Q*
Welfare economics
Q
slide 6
Producer surplus can be measured using the
supply curve for a product.
S
P
Supply of tacos
P'
Q'
Welfare economics
Q
slide 7
The shaded area is the cost of producing
Q' of tacos. If the firm can sell at P', the
total receipts are P' times Q'.
P
Supply of tacos
Click to see the
area that equals
firms' revenues.
P'
Total revenue
equals P'
times Q'.
Q'
Welfare economics
Q
slide 8
Producer surplus is the shaded area.
S
P
Supply of tacos
P'
Q'
Welfare economics
Q
slide 9
P
When QE is sold at a price of PE,
consumer surplus is A, and producer
surplus is B.
S
PE
A
B
D
QE
Welfare economics
Q
slide 10
Notice on the previous slide that at the
market equilibrium the sum of
producer and consumer surplus
(welfare) is maximized.
Welfare economics
slide 11
P
Suppose Q' is sold at a price P' .
What's the effect on welfare compared
to the market?
S
P"
P*
D
Q'
Welfare economics
Q*
Q
slide 12
Here’s our friendly local monopolist the
Ripoff Cable TV Co. of East Lansing.
The profit maximizing output is Q*,
and the profit maximizing price is p*.
The$/Qfollowing hidden slides
illustrate the
MC
computation of surplus at the
monopolist’s output, and the
P*
deadweight loss due to monopoly.
D
Q*
Welfare economics
Q
Hidden slide
MR
slide 13
The next (hidden) slide shows the effects
on welfare of producing less than the
market amount.
[Type "H" to see the hidden slide.]
Conclusion
If the demand curve (willingness to pay) is a good
measure of the value of a good, and
if the supply curve (the firm's cost) is a good
measure of the cost to society to produce a good,
then the best amount of the good to produce is where
supply and demand are equal.
Welfare economics
slide 19