Chapter 20 Elasticity of Supply and Demand

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1、Elasticity of Demand&Supply20C H A P T E RPrice Elasticity of DemandThe law of demand tells us that consumers will respond to a price decrease by buying more of a product(other things remaining constant),but it does not tell us how much more.The degree of responsiveness or sensitivity of consumers t

2、o a change in price is measured by the concept of price elasticity of demand.If consumers are relatively responsive to price changes,demand is said to be elastic.If consumers are relatively unresponsive to price changes,demand is said to be inelastic.Note that with both elastic and inelastic demand,

3、consumers behave according to the law of demand;that is,they are responsive to price changes.The terms elastic or inelastic describe the degree of responsiveness.Price elasticity formulaQuantitative measure of elasticity:Ed=%change in quantity/%change in price.Calculate the percentage change in quan

4、tity by dividing the absolute change in quantity by the original quantity.Calculate the percentage change in price by dividing the absolute change in price by the original price.The percentage change in priceThe percentage change in quantity12Elasticity is.5QPP1P2Q1Q2DMeasures Responsiveness to Pric

5、e ChangesPRICE ELASTICITY OF DEMANDThe percentage change in priceThe percentage change in quantityQPP1P2Q1Q2DCommonly Expressed asPRICE ELASTICITY OF DEMAND%P%QdElasticity is.5PRICE ELASTICITY OF DEMANDElastic DemandEd 42=2Inelastic DemandEd 12=.5Unit ElasticityEd 22=1=Percentages makes it possible

6、to compare elasticities of demand for different products.Because of the inverse relationship between price and quantity demanded,the actual elasticity of demand will be a negative number.However,we ignore the minus sign and use the absolute value of both percentage changes.If the coefficient of elas

7、ticity of demand is a number greater than one,we say demand is elastic;if the coefficient is less than one,we say demand is inelastic.In other words,the quantity demanded is“relatively responsive”when Ed is greater than 1 and“relatively unresponsive”when Ed is less than 1.A special case is if the co

8、efficient equals one;this is called unit elasticity.Note:Inelastic demand does not mean that consumers are completely unresponsive.This extreme situation called perfectly inelastic demand would be very rare,and the demand curve would be vertical.Likewise,elastic demand does not mean consumers are co

9、mpletely responsive to a price change.This extreme situation,in which a small price reduction would cause buyers to increase their purchases from zero to all that it is possible to obtain,is perfectly elastic demand,and the demand curve would be horizontal.Ed=Change inquantitySum ofQuantities/2Chang

10、e inpriceSum ofprices/2 The midpoint formula for elasticity is Ed=(change in Q)/(sum of Qs/2)divided by (change in P)/(sum of Ps/2)Summary of Price elasticitie of Demandrelatively elastic Ed 1,unitary elastic Ed=1,relative inelastic Ed 1,Extreme cases:perfectly elastic Ed=,perfectly inelastic Ed=0.E

11、xtreme CasesPRICE ELASTICITY OF DEMANDPerfectly Inelastic DemandPerfectly Elastic DemandP0P0D1Ed=0D2Ed=QQElasticity varies over range of pricesDemand is more elastic in upper left portion of curve(because price is higher and quantity smaller).Demand is more inelastic in lower right portion of curve(

12、because price is lower and quantity larger).It is impossible to judge elasticity of a single demand curve by its flatness or steepness,since demand elasticity can measure both as elastic and as inelastic at different points on the same demand curve.Total Revenue TestA total-revenue test is the easie

13、st way to judge whether demand is elastic or inelastic.This test can be used in place of an elasticity formula,unless there is a need to determine the elasticity coefficient.Elastic demand and the total-revenue test:Demand is elastic if a decrease in price results in a rise in total revenue,or if an

14、 increase in price results in a decline in total revenue.(Price and revenue move in opposite directions).Inelastic demand and the total-revenue test:Demand is inelastic if a decrease in price results in a fall in total revenue,or an increase in price results in a rise in total revenue.(Price and rev

15、enue move in same direction).Unit elasticity and the total-revenue test:Demand has unit elasticity if total revenue does not change when the price changes.The graphical representation of the relationship between total revenue and price elasticity is shown in Fig.20-2.QPDWhen prices are low,TRQuantit

16、y DemandedPRICE ELASTICITY&TOTAL REVENUESo is total revenueQPDTotal revenue riseswith price to a point.TRQuantity DemandedPRICE ELASTICITY&TOTAL REVENUEQPDTotal revenue riseswith price to a point.then declinesTRQuantity DemandedPRICE ELASTICITY&TOTAL REVENUEQPDTotal revenue riseswith price to a poin

17、t.then declinesTRQuantity DemandedPRICE ELASTICITY&TOTAL REVENUEQPDTotal revenue riseswith price to a point.then declinesTRQuantity DemandedPRICE ELASTICITY&TOTAL REVENUETotal Revenue Test QPDTotal revenue riseswith price to a point.then declinesInelasticDemandInelasticDemandTRQuantity DemandedPRICE

18、 ELASTICITY&TOTAL REVENUEQPDTotal revenue riseswith price to a point.then declinesElasticDemandElasticDemandInelasticDemandTRQuantity DemandedPRICE ELASTICITY&TOTAL REVENUEInelasticDemandQPDTotal revenue riseswith price to a point.then declinesElasticDemandElasticDemandInelasticDemandTRQuantity Dema

19、ndedPRICE ELASTICITY&TOTAL REVENUEInelasticDemandUnitElasticDeterminants of Price Elasticity:1.Substitutes for the product:Generally,the more substitutes,the more elastic the demand.2.The proportion of price relative to income:Generally,the larger the expenditure relative to someones budget,the more

20、 elastic the demand,because buyers notice the change in price more.3.Luxury versus necessary Products:Generally,the less necessary the item,the more elastic the demand.4.Time:Generally,the longer the time period involved,the more elastic the demand becomes.The practical applications of the price ela

21、sticity of demand1.Inelastic demand for agricultural products helps to explain why good crops depress the prices and total revenues for farmers.2.Governments look at elasticity of demand when levying excise taxes.Excise taxes on products with inelastic demand will raise the most revenue and have the

22、 least impact on quantity demanded for those products.3.Demand for drugs is highly inelastic and presents problems for law enforcement.Stricter enforcement reduces supply,raises prices and revenues for sellers,and provides more incentives for sellers to remain in business.Crime may also increase as

23、buyers have to find more money to buy their drugs.Price Elasticity of SupplyThe concept of price elasticity also applies to supply.The elasticity formula is the same as that for demand,but we must substitute the word“supplied”for the word“demanded”everywhere in the formula.Es=percentage change in qu

24、antity supplied/percentage change in priceAs with price elasticity of demand,the midpoints formula is more accurate.Now,compare the immediate market period,the short-run,and long run.PRICE ELASTICITY OF SUPPLYEs=Percentage change in quantitysupplied of good XPercentage change in the price of good XT

25、he ease of shifting resources between alternative uses is very important in price elasticity of supply because it will determine how much flexibility a producer has to adjust his or her output to a change in the price.The degree of flexibility,and therefore the time period,will be different in diffe

26、rent industries.(Figure 20-3)The market period is so short that elasticity of supply is inelastic;it could be almost perfectly inelastic or vertical.In this situation,it is virtually impossible for producers to adjust their resources and change the quantity supplied.(Think of adjustments on a farm o

27、nce the crop has been planted.)PoPQD1QoAn increase indemand withoutenough time tochange supplycausesSmImmediate Market periodPRICE ELASTICITY OF SUPPLYPoPmPQD1QoD2An increase indemand withoutenough time tochange supplycauses anincrease in priceSmImmediate Market periodPRICE ELASTICITY OF SUPPLYPoPQD

28、1QoShort RunPRICE ELASTICITY OF SUPPLYAn increase indemand withless intensitysupply usecauses.SsPoPQD1QoD2Short RunPRICE ELASTICITY OF SUPPLYPsAn increase indemand withless intensitysupply usecauses.a lowerincrease in priceSsQsPoPQD1QoLong RunPRICE ELASTICITY OF SUPPLYAn increase indemand in thelong

29、 run allowsgreater changecausing.SLPoPQD1QoD2Long RunPRICE ELASTICITY OF SUPPLYPLAn increase indemand in thelong run allowsgreater changecausing.SLQLEven more elasticresponse-lessprice increaseThe shortrun supply elasticity is more elastic than the market period and will depend on the ability of pro

30、ducers to respond to price change.Industrial producers are able to make some output changes by having workers work overtime or by bringing on an extra shift.The longrun supply elasticity is the most elastic,because more adjustments can be made over time and quantity can be changed more relative to a

31、 small change in price,as in Figure 20-3c.The producer has time to build a new plant.Applications of the price elasticity of supply.1.Antiques and other non-reproducible commodities are inelastic in supply,sometimes the supply is perfectly inelastic.This makes their prices highly susceptible to fluc

32、tuations in demand.2.Gold prices are volatile because the supply of gold is highly inelastic,and unstable demand resulting from speculation causes prices to fluctuate significantly.Cross Elasticity of Demand:Cross elasticity of demand refers to the effect of a change in a products price on the quant

33、ity demanded for another product.Numerically,the formula is shown for products X and Y.Exy=(percentage change in quantity of X)/(percentage change in price of Y)If cross elasticity is positive,then X and Y are substitutes.If cross elasticity is negative,then X and Y are complements.Note:if cross ela

34、sticity is zero,then X and Y are unrelated,independent products.CROSS ELASTICITY OF DEMANDExy=Percentage change in quantitydemanded of good XPercentage change in the price of good yPositive Sign Goods are SubstitutesNegative SignGoods are ComplementaryZero or Near-Zero ValueGoods are IndependentInco

35、me Elasticity of DemandIncome elasticity of demand refers to the percentage change in quantity demanded that results from some percentage change in consumer incomes.Ei=(%in quantity demanded)/(%in income)A positive income elasticity indicates a normal or superior good.A negative income elasticity indicates an inferior good.Those industries that are income elastic will expand at a higher rate as the economy grows.