Imperfect Competition
AP Microeconomics Topic 4 8:32 English narration · English + 中文 subtitles burned in
Chapters
Transcript
Look outside the textbook.
看看课本之外的世界。
A car company sets its own price.
汽车公司自己定价。
Your city has one water supplier, and no second one to choose.
你所在的城市只有一家自来水公司， 没有第二家可选。
These firms do not take the price, they choose it.
这些企业不是价格的接受者，而是价格的制定者。
That power changes what gets made, what you pay, and who gains.
这种力量改变了产量、你要付的价格，以及谁从中获益。
Here is the plan.
本节的安排是这样的。
First, market power: why marginal revenue sits below price.
首先是市场势力：边际收益为什么低于价格。
Then monopoly, the biggest diagram in this unit.
然后是垄断，本单元最重要的一张图。
Then price discrimination, one good at two prices.
接着是价格歧视，同一件商品两种价格。
Then monopolistic competition, where profit never lasts.
再然后是垄断竞争，那里的利润永远留不住。
And last, oligopoly and game theory.
最后是寡头垄断和博弈论。
Market structures sit on a line.
市场结构排在一条线上。
At the left end, perfect competition: many small firms, one identical product.
最左端是完全竞争：许多小企业，产品完全相同。
Next, monopolistic competition: many firms, each product a little different.
往右是垄断竞争：企业仍然很多，但每家的产品都有一点不同。
Then oligopoly: a few large firms.
再往右是寡头垄断：只有少数几家大企业。
And at the right end, monopoly: one firm, no competition.
最右端是垄断：只有一家企业，没有竞争。
Everything except the far left is imperfectly competitive.
除了最左端以外，其余全都是不完全竞争。
A firm with market power faces a downward-sloping demand curve.
有市场势力的企业面对的是整条需求曲线。
To sell one more unit it must lower the price on all units it sells.
要多卖出一单位， 它必须对卖出的每一单位都降价。
Sell one unit at ninety-nine dollars, and revenue is ninety-nine.
只卖一单位，价格是九十九美元，收入就是九十九。
Sell two, and the price falls to ninety-eight on both, so revenue is one hundred and ninety-six.
卖两单位，价格降到九十八，两单位都是这个价，所以收入是一百九十六。
The second unit added only ninety-seven dollars, less than its own price.
第二单位只带来了九十七美元，比它自己的价格还少。
That is marginal revenue, and it always sits below price.
这就是边际收益，它总是低于价格。
Here is the same idea as a picture.
把同样的道理画成图就是这样。
The demand curve is also the firm's average revenue.
需求曲线同时也是企业的平均收益。
Marginal revenue starts at the same point but falls twice as fast, so it always lies below demand.
边际收益从同一点出发，但下降的速度是两倍，所以它始终位于需求曲线下方。
Remember that shape: every diagram in this unit is built on it.
记住这个形状：本单元的每一张图都建立在它之上。
Here is a monopoly at work.
这就是垄断企业的做法。
It picks the quantity where marginal revenue meets marginal cost, then charges the highest price the demand curve allows, read straight up from that quantity.
它先选定边际收益等于边际成本的产量， 再从这个产量沿着需求曲线向上读出价格——也就是需求曲线允许的最高价。
A monopoly survives because something blocks new firms from getting in.
垄断之所以能存在，是因为有东西挡住了新企业进入。
Four common barriers.
常见的壁垒有四种。
First, very high start-up costs: one big firm supplies the whole market more cheaply than two, and that is a natural monopoly.
第一，极高的启动成本：一家大企业供应整个市场比两家更便宜，那就是自然垄断。
Second, control of a key resource.
第二，控制关键资源。
Third, a patent, the legal right to an invention.
第三，专利，也就是对一项发明的合法权利。
And fourth, a government licence.
第四，政府颁发的许可证。
Barriers are why monopoly profit lasts.
正是这些壁垒，让垄断利润能够持续。
This is the diagram the exam wants. Learn every part.
这就是考试要考的那张图，每一部分都要学会。
Demand is also average revenue.
需求曲线同时也是平均收益。
Marginal revenue lies below it.
边际收益位于它的下方。
Find the quantity where marginal revenue meets marginal cost.
先找到边际收益与边际成本相交处的产量。
Go straight up to the demand curve to read the price.
然后垂直向上到需求曲线，读出价格。
Now add average total cost.
现在把平均总成本加进来。
The gap between price and average total cost is the shaded profit box.
价格与平均总成本之间的差距，就是图中阴影的利润方框。
Entry is blocked, so that profit stays.
因为进入被挡住了，这份利润会一直留着。
So what is wrong with a monopoly?
那么垄断到底哪里不好？
Remember the two steps: produce where marginal revenue equals marginal cost, then charge the price up on demand.
记住那两个步骤：在边际收益等于边际成本处生产， 然后沿着需求曲线向上收取价格。
That price sits above marginal cost.
这个价格高于边际成本。
So the last unit is worth more to buyers than it costs to make, yet nobody makes it.
于是最后那一单位对买家的价值高于它的制造成本，却没有人去生产。
Output is too low, and the value everybody loses is deadweight loss.
产量太低，而所有人损失掉的那部分价值就是无谓损失。
That is what allocatively inefficient means.
这就是配置无效率的意思。
So governments step in.
于是政府出手了。
Antitrust law blocks or breaks up market power.
反垄断法阻止或拆分市场势力。
But some monopolies are useful: nobody wants four sets of water pipes under one street.
但有些垄断是有用的：没有人希望一条街底下埋四套自来水管。
So for a natural monopoly like this power plant, regulators allow one firm and control its price: at marginal cost, the socially optimal price, which is efficient but may cause a loss, or at average total cost — fair-return pricing, where the firm just breaks even.
所以对于像这座电厂这样的自然垄断，监管者允许只有一家企业，但控制它的价格： 定在边际成本，是有效率的，但企业可能亏损； 定在平均总成本，企业就刚好保本。
Now a worked example.
现在做一道例题。
A monopoly faces demand where price equals one hundred minus the quantity, and marginal cost is fixed at twenty.
一家垄断企业面对的需求是：价格等于一百减去产量， 边际成本固定为二十。
Find the quantity and the price.
求产量和价格。
Pause here and try it.
先暂停，自己试一试。
Ready?
好了吗？
Step one: marginal revenue falls twice as fast, so it is one hundred minus twice the quantity.
第一步：边际收益下降的速度是两倍， 所以它等于一百减去两倍的产量。
Step two: set marginal revenue equal to marginal cost, and the quantity comes out at forty.
第二步：令边际收益等于边际成本， 解出产量是四十。
Step three: take forty up to the demand curve, and the price is sixty.
第三步：把四十向上带到需求曲线，价格就是六十。
Sixty against a marginal cost of twenty is a very wide gap: profit, and deadweight loss.
六十对上二十的边际成本，差距非常大：这就是利润，也是无谓损失。
A firm with market power can charge different buyers different prices.
有市场势力的企业，可以对不同的买家收取不同的价格。
That is price discrimination: student tickets are the everyday example.
这就是价格歧视：学生票就是最常见的例子。
First, it needs market power.
第一，它需要市场势力。
Second, a way to separate buyers by what they will pay.
第二，需要办法按支付意愿把买家分开。
Third, a way to prevent resale.
第三，需要办法阻止转售。
At the extreme, perfect price discrimination — first-degree — charges every buyer their own maximum: output becomes efficient and deadweight loss vanishes, but all the consumer surplus is converted into producer surplus, the firm's profit.
在极端情形下，完全价格歧视向每个买家收取他愿付的最高价： 产量变得有效率，无谓损失消失，但全部消费者剩余都变成了利润。
Monopolistic competition sits between the two ends.
垄断竞争位于两端之间。
Many firms, easy entry and exit, but each product is differentiated — a little different from the rest: restaurants, salons, clothing brands.
企业很多，进入和退出都容易， 但每家的产品都有一点不同：餐馆、理发店、服装品牌。
That differentiation gives every firm a little market power, and a downward-sloping demand curve.
这让每家企业都有一点市场势力，以及一条向下倾斜的需求曲线。
In the short run it acts like a small monopoly: marginal revenue equals marginal cost, and profit or loss are both possible.
在短期，它的行为像一个小型垄断者：边际收益等于边际成本，盈利或亏损都有可能。
In the long run, free entry changes everything.
而在长期，自由进入会改变一切。
This firm is making profit, so new firms enter with their own version.
这家企业正在盈利，于是新企业带着自己版本的产品进入市场。
Each rival takes some customers away, so this firm's demand curve slides to the left.
每一个对手都抢走一些顾客，所以这家企业的需求曲线向左移动。
It slides until demand only just touches average total cost, so economic profit falls to zero.
它一直移动，直到需求曲线刚好与平均总成本相切，经济利润降到零。
And look: that point sits left of the lowest point of average total cost.
再看：那个点在平均总成本最低点的左边。
That is excess capacity, and price is still above marginal cost.
这就是过剩产能，而且价格仍然高于边际成本。
The trade-off is variety.
换回来的，是产品的多样性。
Now the last structure: oligopoly.
最后一种结构：寡头垄断。
A few large firms, and the key word is interdependent: each firm's best move depends on its rivals.
少数几家大企业，关键词是相互依存： 每家企业的最优选择，取决于对手怎么做。
If they all agree to cut output and raise the price, they can act like one monopoly.
如果它们一起同意减产、提价，就能像一个垄断者那样行事。
That agreement is collusion, and a formal group is a cartel.
这种约定叫做合谋，正式的组织叫做卡特尔。
But cartels are unstable: every member can earn more by cheating.
但卡特尔并不稳定：每一个成员都能靠违约多赚钱。
To see why, we need game theory.
要弄清原因，我们需要博弈论。
The exam's favourite table.
这就是考试最爱考的表格。
Two firms, A and B, each choosing a high or a low price.
两家企业，A 和 B，各自选择高价或低价。
The numbers are profits: A first, B second. Think like firm A.
表里的数字是利润：A 在前，B 在后。
If B goes high, A gets ten by going high, or fourteen by going low.
站在企业 A 的角度想。
Low wins. If B goes low, A gets four by going high, or six by going low.
如果 B 选高价，A 选高价得十，选低价得十四。
Low wins again.
低价更好。
So low is better regardless of what B does, and that is called a dominant strategy.
如果 B 选低价，A 选高价得四，选低价得六。 低价还是更好。
This table has a name too: a payoff matrix.
所以不论 B 怎么选，低价都更好，这就叫做优势策略。
B's choices are a mirror image, so low is dominant for B too.
B 的情况完全对称，所以低价对 B 也是优势策略。
Both play low and land on six and six.
两家都选低价，落在六和六。
That is the Nash equilibrium: neither firm can do better by changing alone.
这就是纳什均衡：任何一方单独改变都不会更好。
Now look at what they lost.
再看看它们损失了什么。
If both had kept the high price, each would have earned ten.
如果两家都守住高价，各自本可以赚十。
Instead each earns six.
结果各自只赚六。
Both are worse off, and neither did anything stupid: each just followed its own best choice.
两家都变差了，而且谁也没有做傻事： 各自只是选了对自己最好的一步。
That is the prisoners' dilemma, and it is why cartels break down.
这就是囚徒困境，也正是卡特尔会瓦解的原因。
Both firms would gain by colluding, but each has an incentive to cheat, so they end up at the lower-profit outcome. Every member does better if all cooperate, and better still by cheating while others do not.
每个成员在大家都合作时会更好，而在别人守约、自己违约时会更好。
Three marks students give away.
三个学生常常白白丢掉的分。
First, marginal revenue is not price: draw it below demand, twice the slope, every time.
第一，边际收益不是价格： 每一次都要把它画在需求曲线下方，斜率是两倍。
Second, read the monopoly price up on the demand curve, never off the marginal revenue line.
第二，垄断的价格要沿着需求曲线向上读，绝不能从边际收益线上读。
Third, in monopolistic competition the long run gives zero profit, with demand tangent to average total cost.
第三，垄断竞争在长期的利润为零，需求曲线与平均总成本相切。
Get those right and this unit is yours.
把这些做对，这个单元就是你的了。