1 equilibrium molly w. dahl georgetown university econ 101 – spring 2009
TRANSCRIPT
1
Equilibrium
Molly W. DahlGeorgetown UniversityEcon 101 – Spring 2009
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Market Equilibrium
A market is in equilibrium when total quantity demanded by buyers equals total quantity supplied by sellers.
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Market Equilibrium
p
D(p), S(p)
q=D(p)
Marketdemand
Marketsupply
q=S(p)
p*
q*
D(p*) = S(p*): the marketis in equilibrium.
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Market Equilibrium
p
D(p), S(p)
q=D(p)
Marketdemand
Marketsupply
q=S(p)
p*
S(p’)
D(p’) < S(p’): an excessof quantity supplied overquantity demanded.
p’
D(p’)
Market price must fall towards p*.
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Market Equilibrium
p
D(p), S(p)
q=D(p)
Marketdemand
Marketsupply
q=S(p)
p*
D(p”)
D(p”) > S(p”): an excessof quantity demandedover quantity supplied.
p”
S(p”)
Market price must rise towards p*.
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Market Equilibrium
In class: Calculating the market equilibrium when the
market demand and supply curves are linear.Calculating the market equilibrium using the
inverse market demand and supply curves.
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Quantity Taxes
A quantity tax levied at a rate of $t is a tax of $t paid on each unit traded.Excise Tax: tax is levied on sellers.Sales Tax: tax is levied on buyers.
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Quantity Taxes
What is the effect of a quantity tax on a market’s equilibrium?
How are prices affected? How is the quantity traded affected? Who pays the tax? How are gains-to-trade altered?
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Quantity Taxes
A tax rate t makes the price paid by buyers, pb, higher by t from the price received by sellers, ps.
p p tb s
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Quantity Taxes
Even with a tax the market must clear. That is, the quantity demanded by buyers
at price pb must equal quantity supplied by sellers at price ps.
D p S pb s( ) ( )
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Quantity Taxes
p p tb s D p S pb s( ) ( )and
describe the market’s equilibrium.
Notice that these two conditions apply nomatter if the tax is levied on sellers or onbuyers.
Hence, a sales tax rate $t has thesame effect as an excise tax rate $t.
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Quantity Taxes & Market Equilibrium
p
D(p), S(p)
Marketdemand
Marketsupply
p*
q*
No tax
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Quantity Taxes & Market Equilibrium
p
D(p), S(p)
Marketdemand
Marketsupply
p*
q*
An excise taxraises the marketsupply curve by $t,raises the buyers’price and lowers thequantity traded.
$tpb
qt
And sellers receive only ps = pb - t.
ps
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Quantity Taxes & Market Equilibrium
p
D(p), S(p)
Marketdemand
Marketsupply
p*
q*
No tax
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Quantity Taxes & Market Equilibrium
p
D(p), S(p)
Marketdemand
Marketsupply
p*
q*
An sales tax lowersthe market demandcurve by $t, lowersthe sellers’ price andreduces the quantitytraded.$t
pbpb
qt
pb
And buyers pay pb = ps + t.
ps
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Quantity Taxes & Market Equilibrium
p
D(p), S(p)
Marketdemand
Marketsupply
p*
q*
A sales tax levied atrate $t has the sameeffects on themarket’s equilibriumas does an excise taxlevied at rate $t.$t
pbpb
qt
pb
ps
$t
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Tax Incidence
Who pays the tax of $t per unit traded? The division of the $t between buyers and
sellers is the tax incidence.
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Tax Incidence
p
D(p), S(p)
Marketdemand
Marketsupply
p*
q*
pbpb
qt
pb
ps
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Tax Incidence
p
D(p), S(p)
Marketdemand
Marketsupply
p*
q*
pbpb
qt
pb
ps
Tax paid by buyers
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Tax Incidence
p
D(p), S(p)
Marketdemand
Marketsupply
p*
q*
pbpb
qt
pb
psTax paid by sellers
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Tax Incidence
p
D(p), S(p)
Marketdemand
Marketsupply
p*
q*
pbpb
qt
pb
ps
Tax paid by buyers
Tax paid by sellers
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Tax Incidence and Own-Price Elasticities
The incidence of a quantity tax depends upon the own-price elasticities of demand and supply.The incidence of a tax is usually shared,
though not always.
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Tax Incidence and Own-Price Elasticities
p
D(p), S(p)
Marketdemand
Marketsupply
p*
q*
$tpb
qt
ps
As market demandbecomes less own-price elastic, taxincidence shifts moreto the buyers.
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Tax Incidence and Own-Price Elasticities
p
D(p), S(p)
Marketdemand
Marketsupply
p*
q*
$tpb
qt
ps
As market demandbecomes less own-price elastic, taxincidence shifts moreto the buyers.
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Tax Incidence and Own-Price Elasticities
p
D(p), S(p)
Marketdemand
Marketsupply
ps= p*
$tpb
qt = q*
As market demandbecomes less own-price elastic, taxincidence shifts moreto the buyers.
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Tax Incidence and Own-Price Elasticities
Perfectly Inelastic Demand Demander pays all tax
Perfectly Elastic Demand Supplier pays all tax
Perfectly Inelastic Supply Supplier pays all tax
Perfectly Elastic Supply Demander pays all tax
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DWL and Own-Price Elasticities
p
D(p), S(p)
Marketdemand
Marketsupply
p*
q*
$tpb
qt
ps
CS
PS
The tax reducesboth CS and PS,transfers surplusto government,and lowers total surplus.
Tax
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DWL and Own-Price Elasticities
p
D(p), S(p)
Marketdemand
Marketsupply
p*
q*
$tpb
qt
ps
CS
PSTax
Deadweight loss
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DWL and Own-Price Elasticities
p
D(p), S(p)
Marketdemand
Marketsupply
p*
q*
$tpb
qt
ps
Deadweight loss fallsas market demandbecomes less own-price elastic.
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DWL and Own-Price Elasticities
p
D(p), S(p)
Marketdemand
Marketsupply
p*
q*
$tpb
qt
ps
Deadweight loss fallsas market demandbecomes less own-price elastic.
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DWL and Own-Price Elasticities
p
D(p), S(p)
Marketdemand
Marketsupply
ps= p*
$tpb
qt = q*
Deadweight loss fallsas market demandbecomes less own-price elastic.
When demand is perfectly inelastic, the tax causes no deadweight loss.
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DWL and Own-Price Elasticities
Deadweight loss due to a quantity tax rises as either market demand or market supply becomes more own-price elastic.
If either demand or supply are perfectly inelastic, then the deadweight loss is zero.