市場的行為與干預
什麼是市場干預？
市場干預的形式和影響是什麼？
價格干預
價格上限 ，價格下限
數量干預
干預的影響:「剩餘」和「福利」的概念
均衡價格如何受需求面供給面因素的影響？
Supply, Demand, and Government Policies
In a free, unregulated market system, market forces
establish equilibrium prices and exchange quantities.
While equilibrium conditions may be efficient, it may be
true that not everyone is satisfied.
One of the roles of economists is to use their theories
to assist in the development of policies.
How Price Ceilings Affect Market
Outcomes
Two outcomes are possible when the government
imposes a price ceiling:
The price ceiling is not binding (無約束力) if set above the
equilibrium price.
The price ceiling is binding if set below the equilibrium
price, leading to a shortage.
Figure 1 A Market with a Price Ceiling
(a) A Price Ceiling That Is Not Binding
Price of
Ice-Cream
Cone
Supply
$4
Price
ceiling
3
The market clears at
$3 and the price
ceiling is ineffective.
Equilibrium
price
Demand
0
100
Equilibrium
quantity
Quantity of
Ice-Cream
Cones
Figure 1 A Market with a Price Ceiling
(b) A Price Ceiling That Is Binding
Price of
Ice-Cream
Cone
Supply
Equilibrium
price
$3
2
Price
ceiling
Shortage
Demand
0
75
125
Quantity
supplied
Quantity
demanded
Quantity of
Ice-Cream
Cones
How Price Ceilings Affect Market
Outcomes
Effects of Price Ceilings
A binding price ceiling creates
Shortages because QD > QS.
•Example: Gasoline shortage of the 1970s
Nonprice rationing
•Examples: Long lines, discrimination by sellers
CASE STUDY: Lines at the Gas Pump
In 1973, OPEC raised the price of crude oil in world
markets. Crude oil is the major input in gasoline, so
the higher oil prices reduced the supply of gasoline.
What was responsible for the long gas lines?
Economists blame government regulations that
limited the price oil companies could charge for
gasoline.
Figure 2 The Market for Gasoline with a
Price Ceiling
(a) The Price Ceiling on Gasoline Is Not Binding
Price of
Gasoline
Supply, S1
1. Initially,
the price
ceiling
is not
binding . . .
Price ceiling
P1
Demand
0
Q1
Quantity of
Gasoline
Figure 2 The Market for Gasoline with a
Price Ceiling
(b) The Price Ceiling on Gasoline Is Binding
Price of
Gasoline
S2
2. . . . but when
supply falls . . .
S1
P2
Price ceiling
3. . . . the price
ceiling becomes
binding . . .
P1
4. . . .
resulting
in a
shortage.
Demand
0
QS
QD Q1
Quantity of
Gasoline
Price Restrictions
Price Ceilings
The maximum legal price that can be charged
Examples:
• Gasoline prices in the 1970s
• Housing in New York City
• Proposed restrictions on ATM fees
Price Floors
The minimum legal price that can be charged.
Examples:
• Minimum wage
• Agricultural price supports
Full Economic Price
The dollar amount paid to a firm under a price ceiling, plus the
nonpecuniary price.
PF = Pc + (PF - PC)
PF = full economic price
PC = price ceiling
PF - PC = nonpecuniary price
An Example from the 1970s
Ceiling price of gasoline - $1
3 hours in line to buy 15 gallons of gasoline
Opportunity cost: $5/hr
Total value of time spent in line: 3  $5 = $15
Non-pecuniary price per gallon: $15/15=$1
Full economic price of a gallon of gasoline: $1+$1=2
Housing Markets and Rent Ceilings
價格上限
The 1906 earthquake in San Francisco left 200,000
people—more than half the city—homeless.
By the time the San Francisco Chronicle started publishing
again, a month after the earthquake, there was not a
single mention of a housing shortage.
The classified advertisements listed many more houses
and flats for rent than the advertisements for houses and
flats wanted.
How did the market achieve this outcome?
Housing Markets and Rent Ceilings
The Market Response to a
Decrease in Supply
Figure 6.1 shows the San
Francisco housing market
before the earthquake.
The quantity of housing
was 100,000 units and the
rent was $16 a month at
the intersection of D and
SS.
Housing Markets and Rent Ceilings
The earthquake decreased
the supply of housing and
the supply curve shifted
leftward to SSA.
The rent increased to $20
a month and the quantity
decreased to 72,000 units.
Housing Markets and Rent Ceilings
Long-Run Adjustments
The long-run supply of
housing is perfectly elastic
at $16 a month.
With the rent above $16 a
month, new houses and
apartments are built.
Housing Markets and Rent Ceilings
供給的減少使租金上漲,吸
引新的供給
而新增加的供給使租金下降
The quantity of housing
increases and the rent falls
to the pre-earthquake
levels (other things
remaining the same).
Housing Markets and Rent Ceilings
A Regulated Housing Market
A price ceiling 價格上限 is a regulation that makes it
illegal to charge a price higher than a specified level.
When a price ceiling is applied to a housing market it is
called a rent ceiling.房租上限
If the rent ceiling is set above the equilibrium rent, it has
no effect. The market works as if there were no ceiling.
But if the rent ceiling is set below the equilibrium rent, it
has powerful effects.
Housing Markets and Rent Ceilings
the effects of a rent ceiling
that is set below the
equilibrium rent.
The equilibrium rent is $20
a month.
A rent ceiling is set at $16
a month.
So the equilibrium rent is
in the illegal region.
Housing Markets and Rent Ceilings
At the rent ceiling, the
quantity of housing
demanded exceeds the
quantity supplied and
there is a housing
shortage.
價格上限造成供不應求
（短缺）
Housing Markets and Rent Ceilings
With a housing shortage,
people are willing to pay
$24 a month.
Because the legal price
cannot eliminate the
shortage, other
mechanisms operate:
 search activity
搜尋行為(與成本)增加
 black markets 黑市
Figure 3 Rent Control in the Short Run
and in the Long
(a) RentRun
Control in the Short Run
(supply and demand are inelastic)
Rental
Price of
Apartment
Supply
Controlled rent
Shortage
Demand
0
Quantity of
Apartments
Figure 3 Rent Control in the Short Run
and in the Long
Run
(b) Rent
Control in the Long Run
(supply and demand are elastic)
Rental
Price of
Apartment
Supply
Controlled rent
Shortage
0
Demand
Quantity of
Apartments
Housing Markets and Rent Ceilings
Search Activity
The time spent looking for someone with whom to do
business is called search activity.
When a price is regulated and there is a shortage, search
activity increases.
Search activity is costly and the opportunity cost of
housing equals its rent (regulated) plus the opportunity
cost of the search activity (unregulated).
Because the quantity of housing is less than the quantity
in an unregulated market, the opportunity cost of housing
exceeds the unregulated rent.
Housing Markets and Rent Ceilings
Black Markets
A black market is an illegal market that operates
alongside a legal market in which a price ceiling or other
restriction has been imposed.
A shortage of housing creates a black market in housing.
Illegal arrangements are made between renters and
landlords at rents above the rent ceiling—and generally
above what the rent would have been in an unregulated
market.
Housing Markets and Rent Ceilings
Inefficiency of Rent Ceilings
A rent ceiling leads to an inefficient use of resources.
The quantity of rental housing is less than the efficient
quantity and there is a deadweight loss, 無謂的損失
A rent ceiling is also, usually, unfair.
It does not generally benefit the poor.
Rather, it hurts the mobile newcomers and favors the less
mobile, established residents.
Impact of a Price Floor
Price
Surplus
S
PF
P*
D
Qd
Q*
QS
Quantity
Comparative Static Analysis
How do the equilibrium price and quantity change
when a determinant of supply and/or demand
change?
The Labor Market and the Minimum Wage
New, labor-saving technologies become available every
year, which mainly replace low-skilled labor.
Does the persistent decrease in the demand for low-skilled
labor depress the wage rates of these workers?
The immediate effect of these technological advances is a
decrease in the demand for low-skilled labor, a fall in the
wage rate, and a decrease in the quantity of labor supplied.
Figure 6.4 on the next slide illustrates this immediate effect.
The Labor Market and the Minimum Wage
A decrease in the demand
for low-skilled labor is
shown by a leftward shift
of the demand curve.
A new labor market
equilibrium arises at a
lower wage rate and a
smaller quantity of labor
employed.
低技術勞工的需求減少,使
均衡工資下降
The Labor Market and the Minimum Wage
In the long run, people get
trained to do higher-skilled
jobs.
The supply of low-skilled
labor decreases, which is
shown by a leftward shift
of the short-run supply
curve.
當勞工技能提昇,離開低階
市場,供給減少,回到原來工
資水準 例如 家事服務 居
家看護
The Labor Market and the Minimum Wage
If long-run supply is
perfectly elastic, the
equilibrium wage rate
returns to its initial level
(other things remaining the
same).
The Labor Market and the Minimum Wage
The Minimum Wage
A price floor 價格下限 is a regulation that makes it
illegal to trade at a price lower than a specified level.
When a price floor is applied to labor markets, it is called a
minimum wage.最低工資
If the minimum wage is set below the equilibrium wage
rate, it has no effect. The market works as if there were no
minimum wage.
If the minimum wage is set above the equilibrium wage
rate, it has powerful effects.
The Labor Market and the Minimum Wage
If the minimum wage is set above the equilibrium wage
rate, the quantity of labor supplied by workers exceeds the
quantity demanded by employers. There is a surplus of
labor.
Because employers cannot be forced to hire a greater
quantity than they wish, the quantity of labor hired at the
minimum wage is less than the quantity that would be
hired in an unregulated labor market.
Because the legal wage rate cannot eliminate the surplus,
the minimum wage creates unemployment
.
The Labor Market and the Minimum Wage
The equilibrium wage rate
is $4 an hour.
The minimum wage rate is
set at $5 an hour.
So the equilibrium wage
rate is in the illegal region.
The Labor Market and the Minimum Wage
The quantity of labor
employed is the quantity
demanded.
The quantity of labor
supplied exceeds the
quantity demanded.
Unemployment失業is the
gap between the quantity
demanded and the
quantity supplied.
The Labor Market and the Minimum Wage
The Minimum Wage in Practice
The United States has passed the Fair Standards Labor
Act, which currently sets the minimum wage at $5.15 per
hour.
This minimum wage has historically fluctuated between 35
percent and 50 percent of the average wage of production
workers.
Most economists believe that minimum wage laws
increase the unemployment rate of low-skilled younger
workers.最低工資反而可能增加低階勞工的失業
Consumer Surplus (消費者剩餘):
The value consumers get from a good but do not have
to pay for.
I got a great deal!
That company offers a lot of bang
for the buck!
Dell provides good value.
Total value greatly exceeds total
amount paid.
Consumer surplus is large.
I got a lousy deal!
That car dealer drives a hard
bargain!
I almost decided not to buy it!
They tried to squeeze the very
last cent from me!
Total amount paid is close to
total value.
Consumer surplus is low.
Consumer Surplus:
The Discrete Case
Price
10
Consumer Surplus:
The value received but not
paid for
8
6
4
2
D
1
2
3
4
5
Quantity
Consumer Surplus:
The Continuous Case
Price $
10
Value
of 4 units
8
Consumer
Surplus
6
4
Total Cost of 4 units
2
D
1
2
3
4
5
Quantity
Producer Surplus (生產者剩餘):
The amount producers receive in excess of the amount necessary
to induce them to produce the good.
Price
S0
P*
Producer
Surplus
Q*
Quantity
Market Equilibrium
Balancing supply and demand
QxS = Qxd
Steady-state
均衡(equilibrium)
一種不會自發性地改變的狀態
Taxes 稅
Who Pays a Sales Tax?
Demand and supply analysis shows how the buyer and
the seller share the payment of a tax.
Buyers respond to the price with the tax, because that is
the price they must pay.
Sellers respond to the price without the tax, because that
is the price they receive.
The tax is a wedge between the price paid and price
received, which changes the incentives faced by buyers
and sellers.
Elasticity and Tax Incidence
What was the impact of tax?
Taxes discourage market
activity.
When a good is taxed, the
quantity sold is smaller.
Buyers and sellers share the
tax burden.
Taxes
the effects of a sales tax
on CD players.
The equilibrium price with
no tax is $100.
A tax of $10 per CD player
is introduced.
The curve S + tax shows
the new supply curve.
Taxes
The vertical distance
between the original
supply curve and the
supply curve with the tax
is equal to the amount of
the sales tax.
Buyers would have to pay
$110 to induce firms to
offer the original quantity
for sale.
Taxes
The tax changes the
equilibrium price and
quantity.
The quantity decreases.
The price paid by the
buyer rises to $105 and
the price received by the
seller falls to $95.
Taxes
The government collects a
tax revenue on the
decreased quantity.
The buyer and the seller
share the tax payment.
In this example, they share
it equally.
But it doesn’t always turn
out that way.
Taxes
The division of the tax between the buyer and the seller
depends on the elasticities of demand and supply.
Tax Division and Elasticity of Demand
To see the effect of the elasticity of demand on the division
of the tax payment, we look at two extreme cases.
 Perfectly inelastic demand: the buyer pays the entire tax.
 Perfectly elastic demand: the seller pays the entire tax.
 The more inelastic the demand, the larger is the buyers’
share of the tax.
Taxes
In this figure, demand is
perfectly inelastic—the demand
curve is vertical.
需求沒有彈性時,需求綫是垂直的,
消費者負擔所有稅賦
When a tax is imposed on this
good, the buyer pays the entire
tax.
Taxes
In this figure, demand is
perfectly elastic—the demand
curve is horizontal.
When a tax is imposed on this
good, the seller pays the entire
tax.
需求非常有彈性時,需求綫是水平
的,供給者負擔所有稅賦
Taxes
Tax Division and Elasticity of Supply
To see the effect of the elasticity of supply on the division
of the tax payment, we again look at two extreme cases.
 Perfectly inelastic supply: the seller pays the entire tax.
 Perfectly elastic supply: the buyer pays the entire tax.
 The more elastic the supply, the larger is the buyers’
share of the tax.
Taxes
In this figure, supply is perfectly
inelastic—the supply curve is
vertical.
When a tax is imposed on this
good, the seller pays the entire
tax.
供給沒有彈性時,供給綫是垂直的,
供給者負擔所有稅賦
Taxes
In this figure, supply is perfectly
elastic—the supply curve is
horizontal.
When a tax is imposed on this
good, the buyer pays the entire
tax.
供給非常有彈性時,供給綫是水平
的,消費者負擔所有稅賦
Taxes
Sales Taxes in Practice
Taxes usually are levied on goods and services with an
inelastic demand.
The quantity purchased does not decrease by much after
the tax is imposed.
The government collects relatively larger tax receipts.
Taxes
Taxes and Efficiency
Except in the extreme
cases of perfectly inelastic
demand or supply when
the quantity remains the
same, imposing a tax
creates inefficiency.
Figure 6.9 shows the
inefficiency created by a
$10 tax on CD players.
Taxes
With no tax, the market is
efficient and the sum of
consumer surplus and
producer surplus is
maximized.
A tax shifts the supply
curve, decreases the
equilibrium quantity, raises
the price to the buyer, and
lowers the price to the
seller.
Taxes
The tax revenue takes part
of the consumer surplus
and producer surplus.
The decreased quantity
creates a deadweight loss.
無謂的損失
Elasticity and Tax Incidence
In what proportions is the
burden of the tax divided?
How do the effects of
taxes on sellers compare
to those levied on buyers?
The answers to these
questions depend on the
elasticity of demand and
the elasticity of supply.
Figure 9 How the Burden of a Tax Is
Divided
(a) Elastic Supply, Inelastic Demand
Price
1. When supply is more elastic
than demand . . .
Price buyers pay
Supply
Tax
2. . . . the
incidence of the
tax falls more
heavily on
consumers . . .
Price without tax
Price sellers
receive
3. . . . than
on producers.
0
Demand
Quantity
Figure 9 How the Burden of a Tax Is
Divided
(b) Inelastic Supply, Elastic Demand
Price
1. When demand is more elastic
than supply . . .
Price buyers pay
Supply
Price without tax
3. . . . than on
consumers.
Tax
Price sellers
receive
0
2. . . . the
incidence of
the tax falls
more heavily
on producers . . .
Demand
Quantity
勞委會的看護工政策
巴氏量表將不再是衡量聘雇外勞的唯一依據，未來將改由
「醫療評估小組」來決定，只有被小組認定需要二十四小時
照顧，同時找不到本國看護的病人，才能申請外籍監（看）
護工。至於找尋本國看護的辦法，是根據勞委會訂定的二十
四小時照護「每月合理薪資三萬元至三萬五千元」，招募本
國籍看護。每雇用一名本國看護，政府每月發給雇主雇用獎
助金五千元，最長補助一年。
如果是在北高等人口密集都會區，能夠擔任居住在家中，二
十四小時照顧老病，且要處理相關飲食、洗滌、大小便的本
國勞工，現在的行情是每天兩千元，每月六萬元，而且很難
找到年紀比較輕、體力比較好、有能力負擔工作壓力的適當
本勞。
P’
每
月 P*=6
工
資
0.5 萬元
萬
元
每
月
工
資
萬
元
2.5
Q’
Q* Q’
本國勞工雇用數
Q*
外國勞工雇用數
Elasticity and Tax Incidence
So, how is the burden of the tax divided?
The burden of a tax falls more
heavily on the side of the
market that is less elastic.
Price controls include price ceilings and price floors.
A price ceiling is a legal maximum on the price of a
good or service.
An example is rent control.
A price floor is a legal minimum on the price of a good
or a service.
An example is the minimum wage.
Taxes are used to raise revenue for public purposes.
When the government levies a tax on a good, the
equilibrium quantity of the good falls.
A tax on a good places a wedge between the price paid
by buyers and the price received by sellers.
The incidence of a tax refers to who bears the burden
of a tax.
The incidence of a tax does not depend on whether the
tax is levied on buyers or sellers.
The incidence of the tax depends on the price
elasticities of supply and demand.
The burden tends to fall on the side of the market that
is less elastic.