06均衡与拍卖(09-10-23).ppt

6 均衡与拍卖 6 1市场均衡 MarketEquilibrium Amarketisinequilibriumwhentotalquantitydemandedbybuyersequalstotalquantitysuppliedbysellers 在某价格下 市场需求量等于市场供给量 此时的价格为市场均衡价格 此时的数量为均衡数量 6 1 1均衡的确定 p q q D p Marketdemand Marketsupply q S p p q D p S p themarketisinequilibrium MarketEquilibrium S p D p S p anexcessofquantitysuppliedoverquantitydemanded p p D p Marketpricemustfalltowardsp MarketEquilibrium D p D p S p anexcessofquantitydemandedoverquantitysupplied p S p Marketpricemustrisetowardsp p Twospecialcases whenquantitysuppliedisfixed independentofthemarketprice andwhenquantitysuppliedisextremelysensitivetothemarketprice 6 1 2比较静态学 需求变动对市场均衡的影响供给变动对市场均衡的影响需求和供给同时变动对市场均衡的影响 均衡的变动 供求同时变动对均衡的影响 6 2税负与Pareto最优 6 2 1从量税与市场均衡从量税收对市场均衡有何影响 如何影响价格 对均衡数量有何影响 由谁来负担税收 税收对社会福利有何影响 从量税 税率为t 买者支付的价格为pb 卖者得到的价格为ps 则有 在征收税收的情况下 市场均衡条件变为 从量税与市场均衡 均衡价格增加 均衡数量降低卖者只得到了ps pb t t pb qt ps 6 2 2谁承担了税收 Taxpaidbybuyers Taxpaidbysellers 弹性与税收的转嫁 税收的负担比例与该产品的需求弹性和供给弹性的大小相关 假定 需求曲线p a bq供给曲线p c dq每销售一单位产品需付税t销售者和购买者各负担多少 q O P S S D D q p ST ST A B C t D D A B C D D B C A 弹性与税收的转嫁 q O P S S D D q p ST ST A B C t S S ST ST t A B C S S ST ST t A B C 弹性与税收的转嫁 6 2 3税收的福利损失 税收对社会福利的影响 即消费者剩余变动和生产者剩余变动之和 税收的福利损失和自价格弹性 如果eD 0或eS 0 则社会福利损失为零 税收的福利损失和自价格弹性 p 市场需求 市场供给 p q 不征税的情形 q 无税收时的福利 CS PS 税收的福利损失 CS PS Tax 福利损失 税收的福利损失 税收的福利损失和自价格弹性 p q p q t pb qt ps 税收的福利损失和自价格弹性 p q p q t pb qt ps 税收的福利损失和自价格弹性 p q ps p t pb qt q 6 3Auctions WhoUsesAuctions Ownersofart cars stamps machines mineralrightsetc Whyauction Becausemanymarketsareimperfectanditishardtodiscoverpotentialbuyers truevaluationsofyourasset Auctionshelptodiscoverthisinformation 6 3 1TypesofAuctions Englishauction bidsarepublicannouncementsbidpricerisesuntiltherearenofurtherbidshighestbidwinswinnerpayshisbid 通常以保留价格起拍 每一个出价都要超出前一个出价某个最小的竞价增量 网上英式拍卖 传统拍卖对每件拍卖品来说 不需要事先确定拍卖时间 一般数分钟即可结束拍卖 而对于网上拍卖来说 则需要事先确定拍卖的起止时间 一般是数天或数周 例如 在eBay拍卖站点 拍卖的持续时间一般是7天 由于网上拍卖的持续时间较长 这使得许多网上竞买人具有 狙击 Sniping 情况 即直到拍卖结束前的最后数分钟才开始出价 试图提交一个能击败所有其他竞买人的出价 并使得其他竞买人没有时间进行反击 解决办法 解决在拍卖的最后时刻出价的一种方式是在固定的时期内增加 扩展期 例如 扩展期设定为五分钟 这意味着如果在最后五分钟内有出价 则拍卖的关闭时间自动延长五分钟 这一过程一直持续下去 直到五分钟以内没有出价 拍卖才终止 这种方式有效地解决了 狙击 现象 另一种方式是实施 代理竞价 机制 例如 eBay解释它的代理系统为 每一个竞买人都有一个代理帮助出价 竞买人只需告诉代理希望为该物品支付的最高价格 代理会自动出价 直到达到最高价格 英式拍卖的缺点 英式拍卖的缺点是 既然获胜的竞买人的出价只需比前一个最高价高一点 那么每个竞买人都不愿马上按照其预估价出价 另外 竞买人要冒一定的风险 他可能会被令人兴奋的竞价过程吸引 出价超出了预估价 这种心理现象称为 赢者诅咒 Winner sCurse TypesofAuctions Sealed bidfirst priceauction bidsareprivateinformationbidsaremadesimultaneouslyhighestbidwinswinnerpayshisbid TypesofAuctions Sealed bidsecond priceauction bidsareprivateinformationbidsaremadesimultaneouslyhighestbidderwinswinnerpayssecond highestbidalsoknownasaVickreyauction TypesofAuctions Dutchauction 荷兰式拍卖 auctioneerannouncesahighbidandthengraduallylowersthebidfirstbuyertoacceptwinsandpaysthatprice ReservePrice Asellerspecifiedbidlevelbelowwhichnosaleismade 6 3 2Economists ClassificationofAuctions 个人价值拍卖 Private valueauctions everypotentialbuyerknowsforsureherownvaluationoftheitemforsalealltheseindividualvaluationsareindependentofeachother Economists ClassificationofAuctions 共同价值拍卖 Common valueauctions itemforsalehasthesamevaluetoeverypotentialbuyerpotentialbuyersdifferintheirownestimatesofthiscommonvalue例如 拍卖一个里面装了一定数量钱的钱袋 6 3 3拍卖设计 Goals Paretoefficiency 帕累托有效 maximizationoftheseller sprofit AuctionDesign Paretoefficiency theitemmustselltothebuyerwiththehighestvaluationoftheitem WhichauctionsareParetoefficient AuctionsandEfficiency 不具有保留价格的英国式拍卖能够保证帕累托有效率结果的实现 荷兰式拍卖通常并没有保证评价最高的人一定会赢得商品 Sealed bidfirst priceauctionneednotbeefficient Nobuyerknowsotherbuyers valuations sothehighestvaluationbuyermaybidtoolowandlosetoanotherbidder AuctionsandEfficiencySealed bidsecond priceauctionisParetoefficient WhyUseaReservePrice Supposethereare2buyers Thesellerbelieveseachbuyer svaluationis 20withchance1 2and 50withchance1 2 i e withchance1 4each thesellerbelievesshefacesbuyervaluations 20 20 20 50 50 20 and 50 50 WhyUseaReservePrice UseanEnglishauction Bidsmustberaisedbyatleast 1 Withchance1 4each winningbidswillbe 20 21 21and 50ifthereisnoreserveprice Seller sexpectedrevenueis 20 21 21 50 4 28withnoreserveprice WhyUseaReservePrice Withchance1 4each thesellerbelievesshefacesbuyervaluations 20 20 20 50 50 20 and 50 50 Setareservepriceof 50 Withchance1 4therewillbenosale Withchance3 4thewinningbidwillbe 50 Seller sexpectedrevenueis ReservePriceandEfficiency Thereservepricecausesanefficiencylosssince withchance1 4 thereisnotrade Second Price Sealed BidAuction bidsareprivateinformationbidsaremadesimultaneouslyhighestbidderwinswinnerpayssecond highestbidalsoknownasaVickreyauction Second Price Sealed BidAuction Nobidderknowsanyotherbidder struevaluationoftheitemforsale Yet itisindividuallyrationalforeachbiddertostatetruthfullyhisownvaluation Why E g twobidderswithtruevaluationsv1andv2 Second Price Sealed BidAuction E g twobidderswithtruevaluationsv1andv2 Bidsareb1andb2 Expectedgaintobidder1is Second Price Sealed BidAuction Howisthismaximized Ifv1 b2 thenmaximizetheprob ofwinning i e setb1 v1 Ifv1 b2 thenminimizetheprob ofwinning i e setb1 v1 Eitherway tellingthetruthisbest Second Price Sealed BidAuction Sincetruth tellingisbestforeverybidder thehighestvaluationbidderwillwin Hencethesecond price sealed bidauctionisPareto efficient Common ValueAuctions Theitemforsalehasthesamevaluetoeverypotentialbuyer Potentialbuyersdifferintheirownestimatesofthiscommonvalue Bidderi sestimateisvi v i wherevisthecommonvalueand iisbidderi sestimationerror Common ValueAuctions Ifeverybidistruthful thewinneristhebidderwiththelargestestimationerror isoatruthfulwinnero