微观经济学课件清华大学 Tsinghua Micro Ch15 021025.ppt

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1、ChapterFifteenMarketDemandFromIndividualtoMarketDemandFunctionsThinkofaneconomycontainingnconsumers,denotedbyi=1,…,n.Consumeri’sordinarydemandfunctionforcommodityjisFromIndividualtoMarketDemandFunctionsWhenallconsumersareprice-takers,themarketdemandfunctionforcommodityjisFromIndividualtoMarketDe

2、mandFunctionsp1p1p1201535p1’p1”p1’p1”p1’p1”The“horizontalsum”ofthedemandcurvesofindividualsAandB.ElasticitiesElasticitymeasuresthe“sensitivity”ofonevariablewithrespecttoanother.TheelasticityofvariableXwithrespecttovariableYisOwn-PriceElasticityofDemandQ:Whynotjustusetheslopeofademandcurvetomea

3、surethesensitivityofquantitydemandedtoachangeinacommodity’sownprice?A:Becausethevalueofsensitivitythendependsuponthe(arbitrary)unitsofmeasurementusedforquantitydemanded.ArcandPointElasticitiesAn“average”own-priceelasticityofdemandforcommodityioveranintervalofvaluesforpiisanarc-elasticity,usually

4、computedbyamid-pointformula.Elasticitycomputedforasinglevalueofpiisapointelasticity.ArcOwn-PriceElasticitypiXi*pi’pi’+hpi’-hWhatisthe“average”own-priceelasticityofdemandforpricesinanintervalcenteredonpi’?ArcOwn-PriceElasticitypiXi*pi’pi’+hpi’-hWhatisthe“average”own-priceelasticityofdemandforp

5、ricesinanintervalcenteredonpi’?PointOwn-PriceElasticitypiXi*pi’pi’+hpi’-hWhatistheown-priceelasticityofdemandinaverysmallintervalofpricescenteredonpi’?Ash®0,PointOwn-PriceElasticitypiXi*pi’Whatistheown-priceelasticityofdemandinaverysmallintervalofpricescenteredonpi’?istheelasticityatthepoint

6、PointOwn-PriceElasticityE.g.Supposepi=a-bXi.ThenXi=(a-pi)/bandTherefore,PointOwn-PriceElasticitypiXi*api=a-bXi*a/ba/2a/2bPointOwn-PriceElasticitypiXi*api=a-bXi*a/ba/2a/2bown-priceelasticown-priceinelastic(own-priceunitelastic)PointOwn-PriceElasticityE.g.ThensoPointOwn-PriceElasticitypiXi*everyw

7、herealongthedemandcurve.RevenueandOwn-PriceElasticityofDemandIfraisingacommodity’spricecauseslittle(alotof)decreaseinquantitydemanded,thensellers’revenuesrise.Henceown-priceinelastic(elastic)demandcausessellers’revenuestori