Information and market power
International Baccalaureate · IB Diploma · Economics · HL Topic 4 7:32 English narration · English + 中文 subtitles burned in
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In 2021 China's market regulator fined Alibaba eighteen point two billion yuan.
2021 年，中国市场监管机构对阿里巴巴罚款 182 亿元。
It had told sellers they could not also sell on rival platforms.
它曾要求商家不得同时在竞争平台上销售。
A firm can only give such orders when people have few other choices: that is market power.
只有当买卖双方几乎没有别的选择时，企业才能下这样的命令：这就是市场力量。
This lesson covers information gaps, market power, and the four market structures.
本课讲信息不对称、市场力量和四种市场结构。
Asymmetric information means one side of a deal knows more than the other.
信息不对称指交易一方比另一方知道得多。
Adverse selection happens before the contract: one side hides facts about itself.
逆向选择发生在签约之前：一方隐瞒了自己的情况。
Moral hazard happens after it: once protected, people take more risk, because someone else pays.
道德风险发生在签约之后：一旦有了保障，人们就会冒更大的风险，因为损失由别人承担。
Buyers cannot tell good used cars from bad ones, so they pay only an average price.
买家分不清二手车的好坏，只愿付平均价格。
Owners of good cars will not sell at that price, so they leave.
好车车主不愿按这个价格卖，于是退出市场。
Now the average car is worse, so buyers offer even less.
剩下的车平均更差，买家出价更低。
In the end, mostly bad cars are left.
最后市场上几乎只剩坏车。
The side that knows less can screen: insurers ask for health checks.
信息少的一方可以筛选：保险公司要求体检。
The side that knows more can signal: a seller offers a warranty.
信息多的一方可以发信号：卖家提供保修。
Governments regulate with labels and licences.
政府用标签和执照进行监管。
An excess keeps some risk with the insured, which reduces moral hazard.
免赔额让投保人自己承担一部分风险，减少道德风险。
Each response has a limit.
每种办法都有局限。
A firm faces demand P equals seventy minus Q over two.
企业面对的需求是 P = 70 − Q/2。
Average revenue is the price, so this is also the AR curve.
平均收益就是价格，所以这也是 AR 曲线。
Marginal revenue falls twice as fast, because to sell one more unit the firm lowers the price on all its units.
边际收益下降速度是它的两倍，因为多卖一件，企业要降低所有产品的价格。
MR is seventy minus Q, and it reaches zero at seventy units, where total revenue is largest.
MR = 70 − Q，在 70 件时为零，此时总收益最大。
Every firm produces where marginal revenue equals marginal cost.
每家企业都在边际收益等于边际成本处生产。
The table shows why revenue slows: from twenty to forty units it rises by eight hundred, from forty to sixty by only four hundred, and then not at all.
表格显示收益增长在放慢：从 20 件到 40 件增加 800，从 40 件到 60 件只增加 400，之后不再增加。
Profit is largest where one more unit adds as much to cost as to revenue.
当多生产一件给成本和收益带来的增量相等时，利润最大。
Compare price with average total cost. Above it, profit is abnormal; equal, normal; below, a loss. Two tests judge efficiency. Allocative efficiency is price equal to marginal cost, so society gets the right amount. Productive efficiency is output at the lowest average cost.
把价格和平均总成本比较：高于它是超额利润，相等是正常利润，低于它是亏损。 效率有两个检验：配置效率是价格等于边际成本，社会得到合适的数量；生产效率是在平均成本最低点生产。
Perfect competition has very many small firms, identical products, no barriers to entry, and perfect information.
完全竞争有非常多的小企业、完全相同的产品、没有进入壁垒，信息完全。
No firm can charge more, because buyers would go elsewhere.
任何企业都不能抬价，否则买家会去别家。
So each firm is a price-taker, and the market price is its demand, its average revenue and its marginal revenue.
所以每家企业都是价格接受者，市场价格就是它的需求、平均收益和边际收益。
At a price of thirty-six, the firm sets MR equal to MC and makes sixteen units.
价格为 36 时，企业按 MR = MC 生产 16 件。
Average cost is twenty-six twenty-five, so abnormal profit is one hundred and fifty-six a day.
平均成本是 26.25，所以每天超额利润为 156。
New firms enter, supply shifts right and the price falls until it reaches the lowest average cost, twenty-four, at ten units.
新企业进入，供给右移，价格一直下降到最低平均成本 24，此时产量为 10 件。
In the long run, price equals marginal cost, so the market is allocatively efficient, and each firm produces at the lowest average cost, so it is productively efficient too.
长期来看，价格等于边际成本，市场具有配置效率；每家企业都在平均成本最低点生产，也具有生产效率。
If price were below average cost, firms would leave until the price rose back to normal profit.
如果价格低于平均成本，企业会退出，直到价格回升到正常利润水平。
A monopoly is one firm with no close substitutes.
垄断是一家没有相近替代品的企业。
It chooses the price and accepts the quantity buyers want.
它决定价格，接受买家愿意购买的数量。
Its power lasts while barriers keep rivals out: economies of scale, patents and licences, control of a resource, strong brands, and network effects.
它的力量只在壁垒挡住对手时才能维持：规模经济、专利和执照、控制资源、强大品牌以及网络效应。
The monopolist uses the same rule.
垄断者用同样的规则。
Marginal revenue meets marginal cost at forty units.
边际收益与边际成本在 40 件处相交。
It charges the highest price buyers will pay for forty, read from the demand curve: fifty.
它按需求曲线收取买家愿为 40 件支付的最高价格：50。
Average cost there is forty-two point five, so abnormal profit is three hundred a day, protected by barriers.
此时平均成本为 42.5，所以每天超额利润 300，并受到壁垒保护。
Under competition, output would go to where price equals marginal cost: sixty units at forty.
在竞争条件下，产量会到价格等于边际成本处：60 件，价格 40。
The monopolist makes twenty fewer and charges ten more.
垄断者少生产 20 件，价格高出 10。
Consumers lose four hundred a day to the firm.
消费者每天有 400 转移给企业。
The units from forty to sixty are never made, though buyers value them above cost: a deadweight loss of two hundred.
40 到 60 件之间的产品没有生产，尽管买家对它们的评价高于成本：这是 200 的无谓损失。
A monopoly is allocatively and productively inefficient, and without rivals its costs may drift up.
垄断既没有配置效率也没有生产效率，没有对手时成本还可能上升。
But size can help: economies of scale can make even the monopoly price lower than small firms could charge, and abnormal profit can pay for research.
但规模也有好处：规模经济可以让垄断价格都低于小企业的价格，超额利润可以用于研发。
Weigh the two.
要两方面权衡。
A water network or a power grid is a natural monopoly: one firm supplies the market more cheaply than two.
供水管网或电网是自然垄断：一家企业供应整个市场比两家更便宜。
Unregulated, it makes sixty units at forty.
不加管制时，它生产 60 件，价格 40。
Pricing at marginal cost gives a hundred and twenty units but a loss of one thousand a day.
按边际成本定价可生产 120 件，但每天亏损 1000。
Pricing at average cost gives a hundred units with normal profit, and needs no subsidy.
按平均成本定价可生产 100 件，获得正常利润，不需要补贴。
Milk-tea shops each have loyal customers, so each faces its own downward-sloping demand.
每家奶茶店都有回头客，所以各自面对向下倾斜的需求。
In the short run one shop makes ten cups at thirty-four and earns a profit of one hundred.
短期内一家店以 34 元卖出 10 杯，赚 100 元利润。
New shops take its customers until demand just touches average cost, at eight cups and twenty-four fifty.
新店不断分走顾客，直到需求曲线刚好与平均成本相切：8 杯，24.5 元。
The shop is left with excess capacity, but consumers get variety.
这家店有过剩产能，但消费者得到了更多选择。
Two airlines choose a high or a low fare.
两家航空公司选择高票价或低票价。
If B is high, A earns twenty with high or twenty-eight with low.
如果 B 定高价，A 定高价得 20，定低价得 28。
If B is low, A earns eight or twelve.
如果 B 定低价，A 得 8 或 12。
Low is better either way: a dominant strategy.
无论如何低价更好：这是占优策略。
Both choose low and earn twelve, the Nash equilibrium, though both would earn twenty by keeping fares high.
双方都选低价各得 12，这是纳什均衡，尽管都维持高价能各得 20。
Firms can collude, agreeing to fix prices or limit output: a cartel, illegal in most countries.
企业可以共谋，约定定价或限产，这就是卡特尔，在大多数国家违法。
Or they collude tacitly, copying a price leader.
也可以默契共谋，跟随价格领导者。
Or they compete, sometimes in a price war.
也可以竞争，有时打价格战。
Because price cuts are copied fast, most prefer non-price competition: brands, advertising and new models.
由于降价很快被跟进，多数寡头更喜欢非价格竞争：品牌、广告和新款产品。
The five largest firms have shares of forty, twenty-five, fifteen, ten and ten per cent.
最大的五家企业份额分别是 40%、25%、15%、10% 和 10%。
The four-firm ratio adds the first four: ninety per cent.
四企业集中度把前四家相加：90%。
But it ignores foreign rivals, hides whether the leader holds forty or eighty-five, and says nothing about behaviour.
但它忽略了外国对手，看不出领头企业占 40% 还是 85%，也说明不了企业的行为。
From perfect competition to monopoly, the number of firms falls and the barriers rise.
从完全竞争到垄断，企业数量减少，壁垒升高。
Perfect competition has normal profit and is efficient.
完全竞争只有正常利润，且有效率。
Monopolistic competition has normal profit but excess capacity.
垄断竞争也只有正常利润，但有过剩产能。
Oligopoly and monopoly often keep abnormal profit and are usually inefficient.
寡头和垄断常常保有超额利润，通常没有效率。
Governments can ban cartels and block mergers, as when Europe fined Google two point four two billion euros.
政府可以禁止卡特尔、阻止并购，比如欧盟曾对谷歌罚款 24.2 亿欧元。
They can cap the prices of natural monopolies, own them, or open the market to foreign firms.
也可以对自然垄断设价格上限、实行国有，或者向外国企业开放市场。
Each has costs: regulators lack information, and state firms may waste.
每种办法都有代价：监管者缺乏信息，国有企业可能浪费。
To finish: information gaps before and after the contract; MR equals MC for every firm; entry drives perfect competition to the lowest average cost; monopoly costs a deadweight loss; and in oligopoly the game explains both collusion and cheating.
总结：信息差距分签约前和签约后；每家企业都在 MR = MC 处生产；进入使完全竞争到达最低平均成本；垄断造成无谓损失；寡头的博弈既解释了共谋也解释了背叛。