经济学应用与分析-chapter3

1、Chapter Three,The Analysis of Market Structure,Part II,The short-run and Long-Run Industry Supply Decision 行业的短期和长期供给,Supply From A Competitive Industry,How are the supply decisions of the many individual firms in a competitive industry to be combined to discover the market supply curve for the enti

2、re industry?,Since every firm in the industry is a price-taker, total quantity supplied at a given price is the sum of quantities supplied at that price by the individual firms.,Supply From A Competitive Industry,Short-Run Supply,In a short-run the number of firms in the industry is, temporarily, fi

3、xed. Let n be the number of firms;i = 1, ,n. Si(p) is firm is supply function.,In a short-run the number of firms in the industry is, temporarily, fixed. Let n be the number of firms;i = 1, ,n. Si(p) is firm is supply function. The industrys short-run supply function is,Short-Run Supply,Supply From

4、A Competitive Industry,Industrys Supply,Supply From A Competitive Industry,p,S1(p),p,S2(p),p,S(p) = S1(p) + S2(p),p”,p”,S1(p”),S1(p”)+S2(p”),S2(p”),Firm 1s Supply,Firm 2s Supply,Industrys Supply,Supply From A Competitive Industry,Supply From A Competitive Industry,Short-Run Industry Equilibrium,In a

5、 short-run, neither entry nor exit can occur. Consequently, in a short-run equilibrium, some firms may earn positive economics profits, others may suffer economic losses, and still others may earn zero economic profit.,Market demand,Short-run industrysupply,pse,Yse,Y,Short-run equilibrium price clea

6、rs themarket and is taken as given by each firm.,Short-Run Industry Equilibrium,pse,Short-Run Industry Equilibrium,Short-Run Industry Equilibrium,Short-Run Industry Equilibrium,In the long-run every firm now in the industry is free to exit and firms now outside the industry are free to enter. The in

7、dustrys long-run supply function must account for entry and exit as well as for the supply choices of firms that choose to be in the industry. How is this done?,Long-Run Industry Supply,Positive economic profit induces entry. Economic profit is positive when the market price pse is higher than a fir

8、ms minimum av. total cost; pse min AC(y). Entry increases industry supply, causing pse to fall. When does entry cease?,Long-Run Industry Supply,Long-Run Industry Supply,Long-Run Industry Supply,Long-Run Industry Supply,Long-Run Industry Supply,Long-Run Industry Supply,Long-Run Industry Supply,Long-R

9、un Industry Supply,Long-Run Industry Supply,Long-Run Industry Supply,Long-Run Industry Supply,Long-Run Industry Supply,Long-Run Industry Supply,Long-Run Industry Supply,S4(p),S3(p),Mkt. Demand,AC(y),MC(y),y,A “Typical” Firm,The Market,p,p,Y,p4,Each firm would produce less again. Eachfirms economic p

10、rofit would be negative.So the fourth firm would not enter.,y4*,P 0,p4,Long-Run Industry Supply,The long-run number of firms in the industry is the largest number for which the market price is at least as large as min AC(y).,Long-Run Industry Supply,第3章,满足三个条件时，实现长期的竞争均衡 行业中所有厂商均得到正常利润 所有厂商的经济利润均为零

11、市场价格是行业供给量与市场需求量相等时的价格,第3章,完全竞争的零经济利润 零经济利润不等于零会计利润 只要会计利润等于隐性成本，意味着厂商的经济资源获得社会的平均收益,Now we can construct the industrys long-run supply curve. Suppose that market demand is large enough to sustain only two firms in the industry.,Long-Run Industry Supply,Long-Run Industry Supply,Suppose that market d

12、emand is large enough to sustain only two firms in the industry. When market demand increases, the market price rises, each firm produces more, and earns a higher economic profit.,Long-Run Industry Supply,Long-Run Industry Supply,Long-Run Industry Supply,Long-Run Industry Supply,Long-Run Industry Su

13、pply,As market demand increases further, the market price rises further, the two incumbent firms each produce more and earn still higher economic profits - until a 3rd firm becomes indifferent between entering and staying out.,Long-Run Industry Supply,Long-Run Industry Supply,S2(p),S3(p),Mkt. Demand

14、,AC(y),MC(y),y,A “Typical” Firm,The Market,p,p,Y,y2*,p2”,p2”,Long-Run Industry Supply,p2”,S2(p),S3(p),Mkt. Demand,AC(y),MC(y),y,A “Typical” Firm,The Market,p,p,Y,y2*,A third firm can now enter, causing all firmsto earn zero economic profits.,p2”,Long-Run Industry Supply,So any further increase in ma

15、rket demand will cause the number of firms in the industry to rise to three.,Long-Run Industry Supply,S2(p),S3(p),Mkt. Demand,AC(y),MC(y),y,A “Typical” Firm,The Market,p,p,Y,y2*,The only relevant part of the short-runsupply curve for n = 2 firms in the industry.,p2”,p2”,Long-Run Industry Supply,How

16、much further can market demand increase before a fourth firm enters the industry?,Long-Run Industry Supply,Mkt. Demand,AC(y),MC(y),y,A “Typical” Firm,The Market,p,p,Y,p3,y3*,S3(p),S4(p),p3,Long-Run Industry Supply,Mkt. Demand,AC(y),MC(y),y,A “Typical” Firm,The Market,p,p,Y,p3,y3*,A 4th firm would no

17、w earn negativeeconomic profits if it entered the industry.,p3,S3(p),S4(p),Long-Run Industry Supply,Long-Run Industry Supply,Long-Run Industry Supply,Continuing in this manner builds the industrys long-run supply curve, one section at-a-time from successive short-run industry supply curves.,Long-Run

18、 Industry Supply,p,Long-Run Industry Supply,AC(y),MC(y),y,A “Typical” Firm,The MarketLong-RunSupply Curve,p,p,Y,y3*,Notice that the bottom of each segment ofthe supply curve is min AC(y).,Long-Run Industry Supply,As each firm gets “smaller” relative to the industry, the long-run industry supply curv

19、e approaches a horizontal line at the height of min AC(y).,Long-Run Industry Supply,AC(y),MC(y),y,A “Typical” Firm,The MarketLong-RunSupply Curve,p,p,Y,y3*,Notice that the bottom of each segment ofthe supply curve is min AC(y).,Long-Run Industry Supply,AC(y),MC(y),y,A “Typical” Firm,The MarketLong-R

20、unSupply Curve,p,p,Y,y*,The bottom of each segment of the supplycurve is min AC(y). As firms get “smaller”the segments get shorter.,Long-Run Industry Supply,Long-Run Industry Supply,AC(y),MC(y),y,A “Typical” Firm,The MarketLong-RunSupply Curve,p,p,Y,y*,In the limit, as firms become infinitesimallysm

21、all, the industrys long-run supplycurve is horizontal at min AC(y).,第3章,行业的长期供给曲线 不能把厂商长期供给曲线加总，得到市场长期供给曲线：因为长期内，厂商有进出 由于长期内厂商的最优产量水平一定处于长期平均成本的最低点，所以，行业长期供给曲线是厂商长期平均成本最低点变动的轨迹 分三种情况：成本不变行业、成本递增行业、成本递减行业,第3章,行业产量扩大对要素需求的增加，不会引起要素价格的上涨，则单位产品的成本不会随产量的扩大而提高，即LAC不变，这样的行业称为成本不变行业 成本不变行业的长期供给曲线(见图),B,S2,Q2,