中级微观经济 学16Chapter SixteenEquilibrium 均衡StructureuMarket equilibriumuQuantity tax and equilibriumuTax incidence （税收分担）uDeadweight loss （额外净损失）Market EquilibriumuA market is in equilibrium when total quantity demanded by buyers equals total quantity supplied by sellers.uAlso called “market is cleared”uSupply may not equal productionMarket EquilibriumpD(p), S(p)q=D(p)Market demandMarket supply q=S(p)Market SettinguCompetitive market Contestable marketMarket EquilibriumpD(p), S(p)q=D(p)Market demandMarket supply q=S(p)p*q*D(p*) = S(p*); the market is in equilibrium.Market EquilibriumpD(p), S(p)q=D(p)Market demandMarket supply q=S(p)p*S(p)D(p) S(p”); an excess of quantity demanded over quantity supplied. p”S(p”)Market EquilibriumpD(p), S(p)q=D(p)Market demandMarket supply q=S(p)p*D(p”)D(p”) S(p”); an excess of quantity demanded over quantity supplied. p”S(p”) Market price must rise towards p*.Market Equilibrium Linear D that is, p* = (a-c)/b.Market quantity supplied is fixed, independent of price.Market EquilibriumS(p) = c+dp, so d=0 and S(p) c.pqD-1(q) = (a-q)/bMarket demandq* = cp* = D-1(q*); that is, p* = (a-c)/b.with d = 0 givep* = (a-c)/bMarket quantity supplied is fixed, independent of price.Market EquilibriumMarket quantity supplied is extremely sensitive to price. S-1(q) = p*.pqp*Market EquilibriumMarket quantity supplied is extremely sensitive to price. S-1(q) = p*.pqp*D-1(q) = (a-q)/bMarket demandq*Market EquilibriumMarket quantity supplied is extremely sensitive to price. S-1(q) = p*.pqp*D-1(q) = (a-q)/bMarket demandq* = a-bp*p* = D-1(q*) = (a-q*)/b so q* = a-bp*Comparative StaticsuShifting demand curves Income Price of other productsuShifting supply curves TechnologyuTaxesQuantity TaxesuA quantity tax levied at a rate of $t is a tax of $t paid on each unit traded.uIf the tax is levied on sellers then it is an excise tax.uIf the tax is levied on buyers then it is a sales tax.Quantity TaxesuWhat is the effect of a quantity tax on a markets equilibrium?uHow are prices affected?uHow is the quantity traded affected?uWho pays the tax?uHow are gains-to-trade altered?Quantity TaxesuA tax rate t makes the price paid by buyers, pb, higher by t from the price received by sellers, ps.Quantity TaxesuEven with a tax the market must clear.uI.e. quantity demanded by buyers at price pb must equal quantity supplied by sellers at price ps.Quantity Taxesand describe the markets equilibrium. Notice that these two conditions apply no matter if the tax is levied on sellers or on buyers. Hence, a sales tax rate $t has the same effect as an excise tax rate $t.Quantity Taxes & Market EquilibriumpD(p), S(p)Market demandMarket supplyp*q*No taxQuantity Taxes & Market EquilibriumpD(p), S(p)Market demandMarket supplyp*q*$tAn excise tax raises the market supply curve by $tQuantity Taxes & Market EquilibriumpD(p), S(p)Market demandMarket supplyp*q*An excise tax raises the market supply curve by $t, raises the buyers price and lowers the quantity traded.$tpbqtQuantity Taxes & Market EquilibriumpD(p), S(p)Market demandMarket supplyp*q*An excise tax raises the market supply curve by $t, raises the buyers price and lowers the quantity traded.$tpbqtAnd sellers receive only ps = pb - t.psQuantity Taxes & Market EquilibriumpD(p), S(p)Market demandMarket supplyp*q*No taxQuantity Taxes & Market EquilibriumpD(p), S(p)Market demandMarket supplyp*q*An sales tax lowers the market demand curve by $t$tQuantity Taxes & Market EquilibriumpD(p), S(p)Market demandMarket supplyp*q*An sales tax lowers the market demand curve by $t, lowers the sellers price and reduces the quantity traded.$tqtpsQuantity Taxes & Market EquilibriumpD(p), S(p)Market demandMarket supplyp*q*An sales tax lowers the market demand curve by $t, lowers the sellers price and reduces the quantity traded.$tpbpbqtpbAnd buyers pay pb = ps + t.psQuantity Taxes & Market EquilibriumpD(p), S(p)Market demandMarket supplyp*q*A sales tax levied at rate $t has the same effects on the markets equilibrium as does an excise tax levied at rate $t.$tpbpbqtpbps$tQuantity Taxes & Market EquilibriumuWho pays the tax of $t per unit traded?uThe division of the $t between buyers and sellers is the incidence of the tax (税收分担).Quantity Taxes & Market EquilibriumpD(p), S(p)Market demandMarket supplyp*q*pbpbqtpbpsQuantity Taxes & Market EquilibriumpD(p), S(p)Market demandMarket supplyp*q*pbpbqtpbpsTax paid bybuyersQuantity Taxes & Market EquilibriumpD(p), S(p)Market demandMarket supplyp*q*pbpbqtpbpsTax paid bysellersQuantity Taxes & Market EquilibriumpD(p), S(p)Market demandMarket supplyp*q*pbpbqtpbpsTax paid bybuyersTax paid bysellersQuantity Taxes & Market EquilibriumuE.g. suppose the market demand and supply curves are linear.Quantity Taxes & Market EquilibriumandQuantity Taxes & Market EquilibriumandWith the tax, the market equilibrium satisfiesandsoandQuantity Taxes & Market EquilibriumandWith the tax, the market equilibrium satisfiesandsoandSubstituting for pb g