Price Change: Income and
Substitution Effects
THE IMPACT OF A PRICE
CHANGE
Economists often separate the
impact of a price change into two
components:
–the substitution effect; and
–the income effect.
THE IMPACT OF A PRICE
CHANGE
The substitution effect involves the
substitution of good x1 for good x2 or vice-
versa due to a change in relative prices of
the two goods.
The income effect results from an increase
or decrease in the consumer’s real income
or purchasing power as a result of the
price change.
The sum of these two effects is called the
price effect.
THE IMPACT OF A PRICE
CHANGE
The decomposition of the price effect
into the income and substitution
effect can be done in several ways
There are two main methods:
(i) The Hicksian method; and
(ii) The Slutsky method
THE HICKSIAN METHOD
Sir John R.Hicks (1904-1989)
Awarded the Nobel Laureate in
Economics (with Kenneth J. Arrrow)
in 1972 for work on general
equilibrium theory and welfare
economics.
THE HICKSIAN METHOD
X2
X1
Ea
I1
xa
Optimal bundle is Ea, on
indifference curve I1.
THE HICKSIAN METHOD
X2
X1
I1
xa
Ea
A fall in the price of X1
The budget line pivots
out from PP*
THE HICKSIAN METHOD
X2
X1
Eb
I1
I2
xa xb
Ea
The new optimum is
Eb on I2.
The Total Price
Effect is xa to xb
THE HICKSIAN METHOD
To isolate the substitution effect we ask….
“what would the consumer’s optimal
bundle be if s/he faced the new lower price
for X1 but experienced no change in real
income?”
This amounts to returning the consumer
to the original indifference curve (I1)
THE HICKSIAN METHOD
X2
X1
Eb
I1
I2
xa xb
Ea
The new optimum is
Eb on I2.
The Total Price
Effect is xa to xb
THE HICKSIAN METHOD
X2
X1
I1
I2
xa xb
Ea
Eb
Draw a line parallel to
the new budget line and
tangent to the old
indifference curve
THE HICKSIAN METHOD
X2
X1
Ec I1
I2
xa xc xb
Ea
Eb
The new optimum on I1 is
at Ec. The movement from
Ea to Ec (the increase in
quantity demanded from
Xa to Xc) is solely in
response to a change in
relative prices
THE HICKSIAN METHOD
X2
X1
I1
I2
Substitution
Effect
Ea
Eb
Ec
This is the
substitution effect.
Xa Xc
THE HICKSIAN METHOD
To isolate the income effect …
Look at the remainder of the total
price effect
This is due to a change in real
income.
THE HICKSIAN METHOD
X2
X1
I1
I2
Income Effect
Ea
Eb
Ec
The remainder of the total
effect is due to a change
in real income. The
increase in real income is
evidenced by the
movement from I1 to I2
Xc
Xb
THE HICKSIAN METHOD
X2
X1
I1
I2
xa xc xb
Sub
Effect
Income
Effect
Ea
Eb
Ec
HICKSIAN ANALYSIS and DEMAND CURVES
22111 xpxpM +=
P1
P1*
22111 xpxpM += ∗
A
A
B
B
C
Hicksian Demand
Curve (A & C)
Marshallian Demand
Curve (A & B)
P
X1
X1
P
A fall in price
from p1 to p1
*
C
HICKSIAN ANALYSIS and DEMAND
CURVES
Hicksian (compensated) demand
curves cannot be upward-sloping
(i.e. substitution effect cannot be
positive)
THE SLUTSKY METHOD
Eugene Slutsky (1880-1948)
Russian economist expelled from the
University of Kiev for participating in
student revolts.
In his 1915 paper, “On the theory of
the Budget of the Consumer” he
introduced “Slutsky Decomposition”.
THE SLUTSKY METHOD
X2
X1
Ea
I1
xa
Optimal bundle is Ea, on
indifference curve I1.
THE SLUTSKY METHOD
X2
X1
I1
xa
Ea
A fall in the price of X1
The budget line pivots
out from PP*
THE SLUTSKY METHOD
X2
X1
Eb
I1
I2
xa xb
Ea
The new optimum is
Eb on I2.
The Total Price
Effect is xa to xb
THE SLUTSKY METHOD
Slutsky claimed that if, at the new prices,
– less income is needed to buy the original
bundle then “real income” has increased
– more income is needed to buy the
original bundle then “real income” has
decreased
Slutsky isolated the change in demand due
only to the change in relative prices by
asking “What is the change in demand
when the consumer’s income is adjusted
so that, at the new prices, s/he can just
afford to buy the original bundle?”
THE SLUTSKY METHOD
To isolate the substitution effect we
adjust the consumer’s money
income so that s/he change can just
afford the original consumption
bundle.
In other words we are holding
purchasing power constant.
THE SLUTSKY METHOD
X2
X1
Eb
I1
I2
xa xb
Ea
The new optimum is
Eb on I2.
The Total Price
Effect is xa to xb
THE SLUTSKY METHOD
X2
X1
Eb
I1
I2
xa xb
Ea
Draw a line parallel
to the new budget
line which passes
through the point
Ea.
THE SLUTSKY METHOD
X2
X1
Eb
I3
I2
xa xb
Ea
The new optimum
on I3 is at Ec. The
movement from Ea
to Ec is the
substitution effect
Ec
xc
THE SLUTSKY METHOD
X2
X1
Eb
I3
I2
xa
Ea
The new optimum
on I3 is at Ec. The
movement from Ea
to Ec is the
substitution effect
Ec
xc
Substitution Effect
THE SLUTSKY METHOD
X2
X1
Eb
I3
I2Ea
The remainder of
the total price effect
is the Income Effect.
The movement from
Ec to Eb.
Ec
xc
Income Effect
xb
THE SLUTSKY METHOD for NORMAL
GOODS
Most goods are normal (i.e. demand
increases with income).
The substitution and income effects
reinforce each other when a normal
good’s own price changes.
THE SLUTSKY METHOD for
NORMAL GOODS
X2
X1
Eb
I3
I2Ea
The income and
substitution effects
reinforce each
other.
Ec
xc xbxa
Since both the substitution and
income effects increase demand
when own-price falls, a normal
good’s ordinary demand curve
slopes downwards.
The “Law” of Downward-Sloping
Demand therefore always applies to
normal goods.
THE SLUTSKY METHOD for NORMAL
GOODS
THE SLUTSKY EQUATION
Let
be the original budget constraint
and let
22111 xpxpM +=
22112 xpxpM += ∗
represent the budget constraint after the
Slutsky compensating variation in income
has been carried out.
THE SLUTSKY EQUATION
X2
X1
Ea
xa
22111 xpxpM +=
22112 xpxpM += ∗
Demand for x1 is
( )Mppxx d
,, 211 =
M2 < M1
THE SLUTSKY EQUATION
M2 - M1
( ) ( )
( )
( ) 11111
11112
111112
2211221112
2211221112
-
-M
-M
-M
-M
pppaspxM
ppxMM
xpxpMM
xpxpxpxpMM
xpxpxpxpMM
∆=∆=∆
=−=∆
=−=∆
−+=−=∆
++=−=∆
∗
∗
∗
∗
∗
∆M=x1∆p1
gives the change in money
income needed to
consume the original
bundle of goods (at EA)
THE SLUTSKY EQUATION
( ) ( )1211211 ,,,, MppxMppxx dd
−=∆ ∗
The demand curve holding M
constant is given by
which is the change in demand for x1 due to
the change in its own price, holding M and
the price of x2 constant
(1)
THE SLUTSKY EQUATION
( ) ( ),,,, 121221 MppxMppxx dd
s −=∆ ∗
The change in demand due to the Slutsky
substitution effect is given by
(3)
( ) ( ),,,, 221121 MppxMppxx dd
m
∗∗
−=∆
The income effect is given by
(2)
THE SLUTSKY EQUATION
( ) ( )121221 ,,,, MppxMppxx dd
s −=∆ ∗
( ) ( )221121 ,,,, MppxMppxx dd
m
∗∗
−=∆
( ) ( )1211211 ,,,, MppxMppxx dd
−=∆ ∗
ms xxx ∆+∆=∆ 1
Given
Claim
Show this by substituting equations (1), (2)
and (3) into equation (4)
(1)
(2)
(4)
(3)
THE SLUTSKY EQUATION
ms xxx ∆+∆=∆ 1
Divide across by ∆p1
111
1
p
x
p
x
p
x ms
∆
∆
+
∆
∆
=
∆
∆
Recall
11 pxM ∆=∆
so 11 )( xMp ∆−=∆
THE SLUTSKY EQUATION
Substituting
11 )( xMp ∆−=∆
111
1
p
x
p
x
p
x ms
∆
∆
+
∆
∆
=
∆
∆
Gives
1
11
1
x
M
x
p
x
p
x ms
∆
∆
−
∆
∆
=
∆
∆ THE
SLUTSKY
EQUATION
THE SLUTSKY METHOD: INFERIOR
GOODS
Some goods are (sometimes) inferior
(i.e. demand is reduced by higher
income).
The substitution and income effects
“oppose” each other when an
inferior good’s own price changes.
THE SLUTSKY METHOD: INFERIOR
GOODS
X2
X1
Eb
I3
I2
Ea
The substitution
effect is as per
usual. But, the
income effect is
in the opposite
direction.
Ec
xcxbxa
xa to xc
xc to xb
GIFFEN GOODS
In rare cases of extreme inferiority,
the income effect may be larger in
size than the substitution effect,
causing quantity demanded to rise
as own price falls.
Such goods are Giffen goods.
Giffen goods are very inferior goods.
THE SLUTSKY METHOD for
INFERIOR GOODS
X2
X1
Eb
I3
I2
Ea
In rare cases of
extreme income-
inferiority, the income
effect may be larger
in size than the
substitution effect,
causing quantity
demanded to fall as
own-price falls.Ec
xb xcxa
xa to xc
xc to xb
SLUTSKY’S EFFECT FOR
GIFFEN GOODS
Slutsky’s decomposition of the effect
of a price change into a pure
substitution effect and an income
effect thus explains why the “Law”
of Downward-Sloping Demand is
violated for very inferior goods.
DECOMPOSITION of TOTAL PRICE EFFECT:
PERFECT COMPLEMENTS
I1
I2 No substitution
effect
X2
X1
A=C
B
Original
Budget
Constraint
New
Budget
Constraint
A fall in the price of X1
DECOMPOSITION of TOTAL PRICE EFFECT
PERFECT SUBSTITUTES
?

Hicks slutsky income and substitution effect

  • 1.
    Price Change: Incomeand Substitution Effects
  • 2.
    THE IMPACT OFA PRICE CHANGE Economists often separate the impact of a price change into two components: –the substitution effect; and –the income effect.
  • 3.
    THE IMPACT OFA PRICE CHANGE The substitution effect involves the substitution of good x1 for good x2 or vice- versa due to a change in relative prices of the two goods. The income effect results from an increase or decrease in the consumer’s real income or purchasing power as a result of the price change. The sum of these two effects is called the price effect.
  • 4.
    THE IMPACT OFA PRICE CHANGE The decomposition of the price effect into the income and substitution effect can be done in several ways There are two main methods: (i) The Hicksian method; and (ii) The Slutsky method
  • 5.
    THE HICKSIAN METHOD SirJohn R.Hicks (1904-1989) Awarded the Nobel Laureate in Economics (with Kenneth J. Arrrow) in 1972 for work on general equilibrium theory and welfare economics.
  • 6.
    THE HICKSIAN METHOD X2 X1 Ea I1 xa Optimalbundle is Ea, on indifference curve I1.
  • 7.
    THE HICKSIAN METHOD X2 X1 I1 xa Ea Afall in the price of X1 The budget line pivots out from PP*
  • 8.
    THE HICKSIAN METHOD X2 X1 Eb I1 I2 xaxb Ea The new optimum is Eb on I2. The Total Price Effect is xa to xb
  • 9.
    THE HICKSIAN METHOD Toisolate the substitution effect we ask…. “what would the consumer’s optimal bundle be if s/he faced the new lower price for X1 but experienced no change in real income?” This amounts to returning the consumer to the original indifference curve (I1)
  • 10.
    THE HICKSIAN METHOD X2 X1 Eb I1 I2 xaxb Ea The new optimum is Eb on I2. The Total Price Effect is xa to xb
  • 11.
    THE HICKSIAN METHOD X2 X1 I1 I2 xaxb Ea Eb Draw a line parallel to the new budget line and tangent to the old indifference curve
  • 12.
    THE HICKSIAN METHOD X2 X1 EcI1 I2 xa xc xb Ea Eb The new optimum on I1 is at Ec. The movement from Ea to Ec (the increase in quantity demanded from Xa to Xc) is solely in response to a change in relative prices
  • 13.
  • 14.
    THE HICKSIAN METHOD Toisolate the income effect … Look at the remainder of the total price effect This is due to a change in real income.
  • 15.
    THE HICKSIAN METHOD X2 X1 I1 I2 IncomeEffect Ea Eb Ec The remainder of the total effect is due to a change in real income. The increase in real income is evidenced by the movement from I1 to I2 Xc Xb
  • 16.
    THE HICKSIAN METHOD X2 X1 I1 I2 xaxc xb Sub Effect Income Effect Ea Eb Ec
  • 17.
    HICKSIAN ANALYSIS andDEMAND CURVES 22111 xpxpM += P1 P1* 22111 xpxpM += ∗ A A B B C Hicksian Demand Curve (A & C) Marshallian Demand Curve (A & B) P X1 X1 P A fall in price from p1 to p1 * C
  • 18.
    HICKSIAN ANALYSIS andDEMAND CURVES Hicksian (compensated) demand curves cannot be upward-sloping (i.e. substitution effect cannot be positive)
  • 19.
    THE SLUTSKY METHOD EugeneSlutsky (1880-1948) Russian economist expelled from the University of Kiev for participating in student revolts. In his 1915 paper, “On the theory of the Budget of the Consumer” he introduced “Slutsky Decomposition”.
  • 20.
    THE SLUTSKY METHOD X2 X1 Ea I1 xa Optimalbundle is Ea, on indifference curve I1.
  • 21.
    THE SLUTSKY METHOD X2 X1 I1 xa Ea Afall in the price of X1 The budget line pivots out from PP*
  • 22.
    THE SLUTSKY METHOD X2 X1 Eb I1 I2 xaxb Ea The new optimum is Eb on I2. The Total Price Effect is xa to xb
  • 23.
    THE SLUTSKY METHOD Slutskyclaimed that if, at the new prices, – less income is needed to buy the original bundle then “real income” has increased – more income is needed to buy the original bundle then “real income” has decreased Slutsky isolated the change in demand due only to the change in relative prices by asking “What is the change in demand when the consumer’s income is adjusted so that, at the new prices, s/he can just afford to buy the original bundle?”
  • 24.
    THE SLUTSKY METHOD Toisolate the substitution effect we adjust the consumer’s money income so that s/he change can just afford the original consumption bundle. In other words we are holding purchasing power constant.
  • 25.
    THE SLUTSKY METHOD X2 X1 Eb I1 I2 xaxb Ea The new optimum is Eb on I2. The Total Price Effect is xa to xb
  • 26.
    THE SLUTSKY METHOD X2 X1 Eb I1 I2 xaxb Ea Draw a line parallel to the new budget line which passes through the point Ea.
  • 27.
    THE SLUTSKY METHOD X2 X1 Eb I3 I2 xaxb Ea The new optimum on I3 is at Ec. The movement from Ea to Ec is the substitution effect Ec xc
  • 28.
    THE SLUTSKY METHOD X2 X1 Eb I3 I2 xa Ea Thenew optimum on I3 is at Ec. The movement from Ea to Ec is the substitution effect Ec xc Substitution Effect
  • 29.
    THE SLUTSKY METHOD X2 X1 Eb I3 I2Ea Theremainder of the total price effect is the Income Effect. The movement from Ec to Eb. Ec xc Income Effect xb
  • 30.
    THE SLUTSKY METHODfor NORMAL GOODS Most goods are normal (i.e. demand increases with income). The substitution and income effects reinforce each other when a normal good’s own price changes.
  • 31.
    THE SLUTSKY METHODfor NORMAL GOODS X2 X1 Eb I3 I2Ea The income and substitution effects reinforce each other. Ec xc xbxa
  • 32.
    Since both thesubstitution and income effects increase demand when own-price falls, a normal good’s ordinary demand curve slopes downwards. The “Law” of Downward-Sloping Demand therefore always applies to normal goods. THE SLUTSKY METHOD for NORMAL GOODS
  • 33.
    THE SLUTSKY EQUATION Let bethe original budget constraint and let 22111 xpxpM += 22112 xpxpM += ∗ represent the budget constraint after the Slutsky compensating variation in income has been carried out.
  • 34.
    THE SLUTSKY EQUATION X2 X1 Ea xa 22111xpxpM += 22112 xpxpM += ∗ Demand for x1 is ( )Mppxx d ,, 211 = M2 < M1
  • 35.
    THE SLUTSKY EQUATION M2- M1 ( ) ( ) ( ) ( ) 11111 11112 111112 2211221112 2211221112 - -M -M -M -M pppaspxM ppxMM xpxpMM xpxpxpxpMM xpxpxpxpMM ∆=∆=∆ =−=∆ =−=∆ −+=−=∆ ++=−=∆ ∗ ∗ ∗ ∗ ∗ ∆M=x1∆p1 gives the change in money income needed to consume the original bundle of goods (at EA)
  • 36.
    THE SLUTSKY EQUATION () ( )1211211 ,,,, MppxMppxx dd −=∆ ∗ The demand curve holding M constant is given by which is the change in demand for x1 due to the change in its own price, holding M and the price of x2 constant (1)
  • 37.
    THE SLUTSKY EQUATION () ( ),,,, 121221 MppxMppxx dd s −=∆ ∗ The change in demand due to the Slutsky substitution effect is given by (3) ( ) ( ),,,, 221121 MppxMppxx dd m ∗∗ −=∆ The income effect is given by (2)
  • 38.
    THE SLUTSKY EQUATION () ( )121221 ,,,, MppxMppxx dd s −=∆ ∗ ( ) ( )221121 ,,,, MppxMppxx dd m ∗∗ −=∆ ( ) ( )1211211 ,,,, MppxMppxx dd −=∆ ∗ ms xxx ∆+∆=∆ 1 Given Claim Show this by substituting equations (1), (2) and (3) into equation (4) (1) (2) (4) (3)
  • 39.
    THE SLUTSKY EQUATION msxxx ∆+∆=∆ 1 Divide across by ∆p1 111 1 p x p x p x ms ∆ ∆ + ∆ ∆ = ∆ ∆ Recall 11 pxM ∆=∆ so 11 )( xMp ∆−=∆
  • 40.
    THE SLUTSKY EQUATION Substituting 11)( xMp ∆−=∆ 111 1 p x p x p x ms ∆ ∆ + ∆ ∆ = ∆ ∆ Gives 1 11 1 x M x p x p x ms ∆ ∆ − ∆ ∆ = ∆ ∆ THE SLUTSKY EQUATION
  • 41.
    THE SLUTSKY METHOD:INFERIOR GOODS Some goods are (sometimes) inferior (i.e. demand is reduced by higher income). The substitution and income effects “oppose” each other when an inferior good’s own price changes.
  • 42.
    THE SLUTSKY METHOD:INFERIOR GOODS X2 X1 Eb I3 I2 Ea The substitution effect is as per usual. But, the income effect is in the opposite direction. Ec xcxbxa xa to xc xc to xb
  • 43.
    GIFFEN GOODS In rarecases of extreme inferiority, the income effect may be larger in size than the substitution effect, causing quantity demanded to rise as own price falls. Such goods are Giffen goods. Giffen goods are very inferior goods.
  • 44.
    THE SLUTSKY METHODfor INFERIOR GOODS X2 X1 Eb I3 I2 Ea In rare cases of extreme income- inferiority, the income effect may be larger in size than the substitution effect, causing quantity demanded to fall as own-price falls.Ec xb xcxa xa to xc xc to xb
  • 45.
    SLUTSKY’S EFFECT FOR GIFFENGOODS Slutsky’s decomposition of the effect of a price change into a pure substitution effect and an income effect thus explains why the “Law” of Downward-Sloping Demand is violated for very inferior goods.
  • 46.
    DECOMPOSITION of TOTALPRICE EFFECT: PERFECT COMPLEMENTS I1 I2 No substitution effect X2 X1 A=C B Original Budget Constraint New Budget Constraint A fall in the price of X1
  • 47.
    DECOMPOSITION of TOTALPRICE EFFECT PERFECT SUBSTITUTES ?