Elasticity Elasticity 1. A definition & determinants of 1. A definition & determinants of elasticity elasticity • Price elasticity Price elasticity 2. Elasticity & consumer expenditure 2. Elasticity & consumer expenditure 3. Measurement of elasticity 3. Measurement of elasticity • Arc method Arc method • Point method Point method 4. Other measures of elasticity 4. Other measures of elasticity
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Elasticity 1. A definition & determinants of elasticity Price elasticityPrice elasticity 2. Elasticity & consumer expenditure 3. Measurement of elasticity.
fig Quantity Price O Q2Q2 Q1Q1 P1P1 S1S1 D a Market supply and demand
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ElasticityElasticity
1. A definition & determinants of elasticity1. A definition & determinants of elasticity• Price elasticityPrice elasticity
3. Measurement of elasticity3. Measurement of elasticity• Arc methodArc method• Point methodPoint method
4. Other measures of elasticity 4. Other measures of elasticity
1. Definitions and determinants1. Definitions and determinants
If price rises, demand will fallIf price rises, demand will fall• By how much?By how much?
• Responsiveness of demand – elasticityResponsiveness of demand – elasticity
DefinitionsDefinitions ‘‘the the responsivenessresponsiveness of demand and of demand and
supply to changes in price’supply to changes in price’ Price elasticity of demand Price elasticity of demand ((PPdd))::
• ‘‘The responsiveness of quantity demanded The responsiveness of quantity demanded to a change in price’to a change in price’
figfigQuantity
Pric
e
O Q2 Q1
P1
S1
D
a
Market supply and demandMarket supply and demand
Quantity
Pric
e
O Q2 Q1
P1
P2
b
S2
S1
D
a
Market supply and demandMarket supply and demand
figfigQuantity
Pric
e
O Q3 Q2 Q1
P1
P2
P3
c
S2
S1
D
D'a
b
Market supply and demandMarket supply and demand
Determinants of Determinants of PPdd
Why does the price elasticity vary?Why does the price elasticity vary?• 1. number and closeness of substitute goods1. number and closeness of substitute goods
The larger the number of substitute goods (that satisfy the The larger the number of substitute goods (that satisfy the
same need), the greater (same need), the greater (PPdd) will be) will be E.g. holidays v. electricityE.g. holidays v. electricity
• 2. 2. the proportion of income spent on the goodthe proportion of income spent on the good If this is high, a price rise will force a substantial reduction in If this is high, a price rise will force a substantial reduction in
demanddemand
• 3. Time3. Time Time to adjust spending patternsTime to adjust spending patterns Short run – inelasticShort run – inelastic Long run - elasticLong run - elastic
2. Elasticity and consumer expenditure2. Elasticity and consumer expenditure
Total expenditure (TE) Total expenditure (TE)
= = P x Q P x Q
= Total Revenue (TR)= Total Revenue (TR)
See figureSee figure
Consumers’ total expenditure Consumers’ total expenditure ==
Unit elastic demand (Unit elastic demand (PPDD = -1)= -1)
3. Measurement of elasticity3. Measurement of elasticity
Elasticity varies along the demand ( & supply) Elasticity varies along the demand ( & supply) curvecurve Price-elastic (>1)Price-elastic (>1) price-inelastic(0-1)price-inelastic(0-1) unitary (=1)unitary (=1)
(1) arc method (between two points on D)(1) arc method (between two points on D) price elasticity of demand: price elasticity of demand: Q/QQ/Q ÷ ÷ P/PP/P using the average or 'mid-point' methodusing the average or 'mid-point' method
Q/average QQ/average Q ÷ ÷ P/average PP/average P
0
2
4
6
8
10
0 10 20 30 40 50
P (£)
Q (000s)
m
n
Q Pmid Q mid PPd =
Demand
Measuring elasticity using the arc methodMeasuring elasticity using the arc method
0
2
4
6
8
10
0 10 20 30 40 50
P (£)
Q (000s)
m
n
Q Pmid Q mid PPd =
10 2 15 7=
= 10/15 x 7/2 = 70/30= 7/3 = 2.33
Demand
Measuring elasticity using the arc methodMeasuring elasticity using the arc method
Measurement of elasticityMeasurement of elasticity
(2) The Point Method(2) The Point Method• Price elasticity of demandPrice elasticity of demand
dQ / dP x P / QdQ / dP x P / Q
• ‘‘d’ – infinitesimally small change (see calculus)d’ – infinitesimally small change (see calculus)
• dQ / dP – rate of change of quantity demanded dQ / dP – rate of change of quantity demanded with respect to pricewith respect to price
P
Q
50
30
0 40 100
D
r
Pd = (1 / slope) x P/Q
Measuring elasticity at a pointMeasuring elasticity at a point
P
Q
50
30
0 40 100
D
r
Pd = (1 / slope) x P/Q
= dQ/dP i.e. invert dP/dQ (-50/100)
= 100/50 =-2 = /40) = -2 (0.75) = 1.5
Measuring elasticity at a pointMeasuring elasticity at a point
4. Other measures of elasticity4. Other measures of elasticity
Income elasticity of demandIncome elasticity of demand ‘…‘…the responsiveness of demand to a change in the responsiveness of demand to a change in
Cross-price elasticity of demandCross-price elasticity of demand ‘…‘…responsiveness of demand for one product to a responsiveness of demand for one product to a
change in the price of another product.’change in the price of another product.’ Substitutes or complementsSubstitutes or complements
Price elasticity of supplyPrice elasticity of supply Definition & determinants?Definition & determinants?