Chapter 13 垄断 Nicholson and Snyder, Copyright ©2008 by Thomson South-Western. All rights reserved.

垄断 A 垄断 is a single supplier to a market 该厂商可以选择在市场需求曲线的任何一点上生产。

进入壁垒 Barriers to Entry Barriers to entry 是所有垄断权力的根源 两种进入壁垒 technical barriers legal barriers

进入的技术进入壁垒 基本的技术壁垒：商品的是那个站在一个大的产出水平范围内呈现边际和平均成本递减 规模相对大厂商为低成本生产者 firms may find it profitable to drive others out of the industry by cutting prices this situation is known as 自然垄断 once the 垄断 is established, entry of new firms will be difficult

进入的技术进入壁垒 另一个技术壁垒为掌握了一项低成本生产技术的特殊知识。 此外，拥有独特资源的权利也是维持垄断的基础。 it may be difficult to keep this knowledge out of the hands of other firms 此外，拥有独特资源的权利也是维持垄断的基础。

法律进入壁垒 Many pure monopolies are created as a matter of law a patent, 专利 an exclusive franchise 服务的特许权

进入壁垒的设立 一些进入壁垒可能来自厂商的行为 垄断者设置进入壁垒的努力可能要付出现实的资源成本。寻租行为 research and development of new products or technologies purchase of unique resources lobbying efforts to gain 垄断 power 垄断者设置进入壁垒的努力可能要付出现实的资源成本。寻租行为

利润最大化 To maximize profits, a monopolist will choose to produce that output level for which 边际收益等于边际成本 MR<P

利润最大化 Since MR = MC at the profit-maximizing output and P > MR for a monopolist, 垄断者设置价格高于边际成本

利润最大化 The monopolist will maximize profits where MR = MC Q* The monopolist will maximize profits where MR = MC Price MC P* The firm will charge a price of P* AC C Profits can be found in the shaded rectangle D MR Quantity

逆弹性规则 Inverse 逆弹性规则 where eQ,P is the elasticity of demand for the entire market

逆弹性规则 垄断者只会在有弹性的需求地方生产 eQ,P < -1 The firm’s “markup” over marginal cost depends inversely on the elasticity of market demand

垄断利润 垄断利润 will be positive as long as P > AC 垄断利润 can continue into the long run because entry is not possible some economists refer to the profits that a 垄断 earns in the long run as 垄断租金 the return to the factor that forms the basis of the 垄断

垄断利润 The size of 垄断利润 in the long run will depend on the relationship between average costs and market demand for the product

垄断利润 Positive profits Zero profit Price Price Quantity Quantity MC MC AC AC P*=AC P* C D D MR MR Q* Quantity Q* Quantity Positive profits Zero profit

没有垄断供给曲线 供给曲线的定义？ 对于一条固定的需求曲线，一个垄断者的供给“曲线”仅仅是一个点 the price-output combination where MR = MC 如果需求曲线移动，边际收益曲线也将移动，将选择一个新的利润最大化的产出 连接由此产生的一系列市场需求曲线上的均衡点没有含义，这个轨迹可能为一个奇怪形状

计算垄断产量 Suppose that the market for frisbees 飞碟为线性需求曲线 or Q = 2,000 - 20P or P = 100 - Q/20 The total costs of the frisbee producer are given by C(Q) = 0.05Q2 + 10,000

计算垄断产量 To maximize profits, MR = MC We need to find total revenue TR = PQ = 100Q - Q2/20 Therefore, marginal revenue is MR = 100 - Q/10 while marginal cost is MC = 0.1Q

计算垄断产量 Thus, MR = MC where At the profit-maximizing output, 100 - Q/10 = 0.01Q Q* = 500 P* = 75 At the profit-maximizing output, C(Q) = 0.05(500)2 + 10,000 = 22,500 AC = 22,500/500 = 45  = (P* - AC)Q = (75 - 45)500 = 15,000

常弹性需求的垄断 Suppose that the demand function is of the form In this case Q = aPe In this case MR = P(1 + 1/e)

常弹性需求的垄断 利润最大化 requires Because e < -1 for 利润最大化, P > MC MR = P(1 + 1/e) = c P = c(e/(1 + e) Because e < -1 for 利润最大化, P > MC the gap will be larger the closer e is to -1

垄断与资源配置 Price If this market was 完全竞争, output would be Q* and price would be P* Q* P* Under a 垄断, output would be Q** and price would rise to P** Q** P** MC=AC D MR Quantity

垄断与资源配置 Consumer surplus would fall Producer surplus will rise Price Consumer surplus would fall Producer surplus will rise Consumer surplus falls by more than producer surplus rises. P** There is a deadweight loss 无谓损失 MC=AC P* D MR Q** Q* Quantity

例13.2 福利损失与弹性 假设需求为指数形式: Q = Pe where e is the price elasticity of demand (e < -1) 边际成本和平均成本为常数c

例13.2 福利损失与弹性 The competitive price in this market will be Pc = c and the 垄断 price is given by

例13.2 福利损失与弹性 任何价格 (P0) 下的消费者剩余 e < -1

例13.2 福利损失与弹性 Therefore, under perfect competition and under 垄断

例13.2 福利损失与弹性 Taking the ratio of these two surplus measures yields If e = -2, this ratio is ½ consumer surplus under 垄断 is half what it is under perfect competition

例13.2 福利损失与弹性 垄断利润 are given by

例13.2 福利损失与弹性 To find the transfer from consumer surplus into 垄断利润 we can divide 垄断利润 by the competitive consumer surplus If e = -2, this ratio is ¼

垄断与产品质量 Market power 将影响 market price，type, quality, or diversity of goods Higher-quality or lower-quality than competitive firms? 取决于消费者需求与厂商的成本性质

垄断与产品质量 假设消费者愿意为质量X 支付由 逆需求函数 P(Q,X) 给定 P/Q < 0 and P/X > 0 If costs are given by C(Q,X), the 垄断 will choose Q and X to maximize  = P(Q,X)Q - C(Q,X)

垄断与产品质量 First-order conditions for a maximum are MR = MC for output decisions the marginal revenue from increasing quality by one unit is equal to the marginal cost of making such an increase

垄断与产品质量 在完全竞争条件下，产品质量的选择水平为最大化净社会福利 Maximizing with respect to X yields

垄断与产品质量 两者的质量水平的差异: 所以，两者即使选择统一产出水平，由于边际值不同，选择不同的质量水平 垄断者着眼于产量Q 在其利润最大时增加以单位质量的边际价值 而完全竞争条件下着眼于所有产出水平平均质量的边际价值 所以，两者即使选择统一产出水平，由于边际值不同，选择不同的质量水平

价格歧视 定义：如果能以不同的价格销售相同单位的产品 Whether 价格歧视 is feasible depends on the inability of buyers to practice arbitrage 套利

一级价格歧视 It may be possible to charge each buyer the maximum price he would be willing to pay for the good perfect or first-degree 价格歧视 extracts all consumer surplus no deadweight loss

一级价格歧视 Under perfect 价格歧视, the monopolist charges a different price to each buyer Price Q1 P1 The first buyer pays P1 for Q1 units Q2 P2 The second buyer pays P2 for Q2-Q1 units The monopolist will continue this way until the marginal buyer is no longer willing to pay the good’s marginal cost MC D Quantity Q2

例13.3 First-Degree 价格歧视 生产飞碟例子

例13.3 First-Degree 价格歧视 Therefore, P = 100 - Q/20 = MC = 0.1Q Q* = 666 Total revenue and total costs will be Profit is much larger (23,333 > 15,000)

市场分割 Perfect 价格歧视 requires the monopolist to know the demand function for each potential buyer We can also assume that a 垄断能够将买者分割到不同的市场中 can follow a different pricing policy in each market 三级价格歧视

市场分割 垄断者需要知道每个市场的需求价格弹性 根据逆弹性规则决定价格 If the marginal cost is the same in all markets,

市场分割 This implies that The profit-maximizing price will be higher in markets where demand is less elastic

市场分割 If two markets are separate, maximum profits occur by setting different prices in the two markets Price The market with the less elastic demand will be charged the higher price P1 P2 MC MC D D MR MR Quantity in Market 1 Q1* Q2* Quantity in Market 2

Third-Degree 价格歧视 Suppose that the inverse demand curves in two separated markets are given by P1 = 24 – Q1 P2 = 12 – 0.5Q2 Suppose that MC = 6 利润最大化 requires that MR1 = 24 – 2Q1 = 6 = MR2 = 12 – Q2

例13.4 三级价格歧视 Optimal choices and prices are Profits for the 垄断 are Q1* = 9 P1* = 15 Q2* = 6 P2* = 9 Profits for the 垄断 are  = (P1 - 6)Q1 + (P2 - 6)Q2 = 81 + 18 = 99

例13.4 三级价格歧视 We can calculate the deadweight losses in the two markets note that the competitive output would be 18 in market 1 and 12 in market 2 DW1 = 0.5(P1-MC)(18-Q1) = 0.5(15-6)(18-9) = 40.5 DW2 = 0.5(P2-MC)(12-Q2) = 0.5(9-6)(12-6) = 9

例13.4 三级价格歧视 If this 垄断 were constrained to charge a single price, it would set P = 15 and sell only in the first market Deadweight loss increases total potential consumer surplus in market 2 is lost DW = DW1 + DW2 = 40.5 + 0.5(12 – 6)(12 – 0) DW = 40.5 + 36 = 76.5

二级价格歧视 价格计划：数量折扣、最小购买要求或“保证金”收费与搭售 使得需求者根据他们自己的意愿支付的价格自动归类 也可获得更高的利润

两部收费制 迪斯尼（曾经），国内大部分游乐园 Linear two-part tariff 固定费和单位产品费用 T(q) = a + pq the monopolist’s goal is to choose a and p to maximize profits, given the demand for the product

两部收费制 Two-Part Tariffs Because the average price paid by any demander is

两部收费制 The tariff is only feasible if resale can be prevented between those who pay a low price and those who pay a high price

两部收费制 利润最大化的一个可行的方法是 厂商设置 p = MC ，然后确定 a，等于最不迫切买者（the least eager buyer）消费时的消费者剩余 this might not be the most profitable approach in general, optimal pricing schedules will depend on a variety of contingencies

例13.5 Two-Part Tariffs Suppose there are two different buyers with the demand functions q1 = 24 - p1 q2 = 24 - 2p2 If MC = 6, one way for the monopolist to implement a two-part tariff would be to set p1 = p2 = MC = 6 q1 = 18 q2 = 12

例13.5 Two-Part Tariffs With this marginal price, demander 2 （最不迫切的买主）obtains consumer surplus of 36 this would be the maximum entry fee that can be charged without causing this buyer to leave the market This means that the two-part tariff in this case would be T(q) = 36 + 6q

例13.5 Two-Part Profits for the firm would be  = T(q1) + T(q2) – AC(q1 + q2)  = 72 + (6 · 30) – (6 ·30) = 72

垄断管制 Natural monopolies such as the utility, communications, and transportation industries are highly regulated in many countries

垄断管制 An enforced policy of marginal cost pricing will cause a natural 垄断 to operate at a loss natural monopolies exhibit declining average costs over a wide range of output

垄断管制 AC MC Because natural monopolies exhibit decreasing costs, MC falls below AC Price P1 Q1 An unregulated 垄断 will maximize profit at Q1 and P1 P2 Q2 If regulators force the 垄断 to charge a price of P2, the firm will suffer a loss because P2 < C2 C1 C2 MR Quantity D

垄断管制 Suppose that the regulatory commission allows the 垄断 to charge a price of P1 to some users P1 Q1 Price Other users are offered the lower price of P2 P2 Q2 The profits on the sales to high-price customers are enough to C1 cover the losses on the sales to low-price customers C2 AC MC Quantity D

垄断管制 One way to avoid this dilemma is the implementation of a multiprice system charge some users a high price maintain a low price for marginal users

垄断管制 The 垄断 could charge some users the high price (P1) and others a low price (P2) Price The profits from one class of user would then subsidize the losses from the other users P1 AC MC P2 Quantity Q1 Q2 D

垄断管制 Another approach would be to allow the 垄断 to charge a price above marginal cost that is sufficient to earn a “fair” rate of return on investment

垄断管制 Suppose that a regulated utility has a production function of the form q = f (k,l) 厂商的资本实际回报率定义为

ℒ = pf (k,l) – wl – vk + [wl + s0k – pf (k,l)] 垄断管制 假设回报率限定为 s0, then the firm’s problem is to maximize profits  = pf (k,l) – wl – vk subject to this constraint The Lagrangian for this problem is ℒ = pf (k,l) – wl – vk + [wl + s0k – pf (k,l)]

垄断管制 If =0, regulation is ineffective and the 垄断 behaves like any profit-maximizing firm If =1, the Lagrangian reduces to ℒ = (s0 – v)k which (assuming s0>v), will mean that the 垄断 will hire infinite amounts of capital

垄断管制 Therefore, 0<<1 and the FOCs for a maximum are: ℒ /l = pfl – w + (w – pfl) = 0 ℒ /k = pfk – v + (s0 – pfk) = 0 ℒ / = wl + s0k – pf (k,l) = 0

垄断管制 Because s0>v and <1, this means that pfk < v The firm will hire more capital than it would under unregulated conditions it will also achieve a lower marginal productivity of capital

Dynamic Views of 垄断 Some economists have stressed the beneficial role that 垄断利润 can play in the process of economic development provide funds that can be invested in research and development provides an incentive to keep one step ahead of potential competitors