Market Failure and the Role of Government
AP Microeconomics Topic 6 8:21 English narration · English + 中文 subtitles burned in
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Transcript
Look at this factory.
看看这座工厂。
Somebody bought what it makes, and somebody was paid to make it.
有人买了它生产的东西，也有人因为生产而拿到报酬。
Both sides are happy with the price.
买卖双方都对价格满意。
But the smoke is not in that price.
但是烟不在这个价格里面。
It lands on people who never agreed to anything.
它落在了从未同意过任何事的人身上。
Here is that trade.
我们把这笔交易画出来。
A factory makes one unit of a chemical, a buyer wants it, and they agree on a price of eight dollars.
一家工厂生产一单位化学品，一位买家想要它， 双方谈好价格是八美元。
Now look downwind.
现在看看下风的方向。
Every unit also drops three dollars of harm on the neighbours, and nobody pays them.
每一单位还会给邻居带来三美元的损害， 而没有人赔偿他们。
So the missing three dollars never reaches the price.
所以缺失的三美元从来没有进入价格。
The good looks too cheap, and so the market makes too much of it.
这件商品看起来太便宜了，于是市场生产得太多。
That gap is today's lesson.
这个缺口就是今天这节课的内容。
Start with the target: a socially efficient outcome, the one that maximises total surplus.
先看目标：社会有效率的结果，也就是让总剩余最大的那一个。
Society does best on the last unit whose benefit to everyone still covers its cost to everyone: marginal social benefit equal to marginal social cost.
当最后一单位带给所有人的收益仍能覆盖它让所有人付出的成本时， 社会的状况最好：也就是边际社会收益等于边际社会成本。
Notice the word social — it counts every cost, whoever pays it.
注意“社会”这两个字——它把每一份成本都算进来，不管由谁承担。
Watch it happen.
我们来看看。
Social benefit falls as we make more, and social cost rises.
随着产量增加，社会收益下降，社会成本上升。
Where they cross is the optimum quantity.
它们相交的地方就是最优数量。
Push past it, and every extra unit costs more than it is worth: the shaded triangle is surplus destroyed.
越过它，每多生产一单位的成本都超过它的价值：阴影三角形就是被毁掉的剩余。
Now go the other way.
现在看另一个方向。
Stop short, and good trades never happen, a loss too.
停得太早，好的交易根本不会发生，这同样是损失。
Either way, the triangle you shade is called the deadweight loss, and drawing it earns marks.
无论哪一边，你涂上阴影的三角形都叫无谓损失，把它画出来就能得分。
Now name the problem.
现在给这个问题起个名字。
An externality is a cost or a benefit that spills onto a third party, someone outside the deal, so buyer and seller ignore it.
外部性是溢出到第三方身上的成本或收益， 而第三方并不在这笔交易里，所以买家和卖家都不理会它。
A negative externality, like pollution, makes society's cost higher than the firm's cost, so the market over-produces.
负外部性，比如污染，让社会成本高于企业成本，于是市场生产过多。
A positive externality, like a vaccine, works the other way.
正外部性，比如疫苗，方向正好相反。
Either way, the gap creates a deadweight loss.
无论哪一种，这个缺口都会造成无谓损失。
Watch the negative case being drawn.
看负外部性这张图是怎么画出来的。
Supply shows only the firm's own cost.
供给曲线只反映企业自己的成本。
Lift it by the external cost and you have the true cost to society.
把它按外部成本抬高，就得到社会真正的成本。
The market stops too far to the right, and the shaded wedge is the welfare loss.
市场停的位置偏右太多，阴影楔形就是福利损失。
The mirror case is tested just as often.
反过来的情形考得一样多。
Take a vaccination: you buy it for yourself, but everyone around you becomes safer too.
就说接种疫苗：你为自己买它， 但你周围的每个人也因此更安全。
That extra benefit spills onto other people, so society's benefit line sits above the demand curve.
这份额外的收益溢出到别人身上， 所以社会的收益线位于需求曲线的上方。
Buyers never counted the extra part, so the market under-produces.
买家从来没有把额外的那部分算进去，所以市场停得太少。
The fix is a subsidy the size of the external benefit, which walks output out to the efficient quantity.
解决办法是一项补贴，规模等于外部收益，它把产量带到有效率的数量。
Here is the toolkit.
这就是政策工具箱。
Size matters more than the name.
定多大比叫什么名字更重要。
A Pigovian tax equals the external cost and pulls output down.
庇古税等于外部成本，把产量拉下来。
A subsidy equals the external benefit and pushes output up.
补贴等于外部收益，把产量推上去。
Tradable permits cap the pollution and let firms trade it.
可交易许可证给污染设上限，并允许企业买卖它。
This slide says it plainly: a thirty-dollar harm needs a thirty-dollar tax.
这张幻灯片说得很清楚：三十美元的损害就需要三十美元的税。
Or a few neighbours may bargain to it themselves — that is the Coase theorem, though it only works when property rights are clear and few people are involved.
或者，少数几个邻居也可能自己谈出结果，这就是科斯的思路。
Now a full exam question, on screen.
现在做一道完整的考试题，题目就在屏幕上。
A chemical does three dollars of damage on every unit; the market makes one hundred, but seventy is best for society.
某种化学品每一单位造成三美元的损害； 市场生产一百单位，但对社会最好的是七十单位。
Pause the video and try it.
先暂停视频，自己试一试。
Ready?
好了吗？
First, the gap: society's cost sits three dollars above the private cost, so three dollars is the triangle's height.
先看缺口：社会成本比私人成本高出三美元，所以三美元就是三角形的高。
Its base is the extra output, one hundred minus seventy, thirty units.
它的底是多出来的产量，一百减七十，三十单位。
So the deadweight loss is one half times thirty times three, forty-five dollars.
所以无谓损失等于二分之一乘三十乘三，四十五美元。
And the policy?
那政策呢？
A per-unit tax of exactly three dollars, sized to the external cost, not the whole cost of the good.
一项每单位正好三美元的从量税，对准外部成本， 而不是整件商品的成本。
Some failures come from the good itself.
有些失灵来自商品本身。
Two questions.
问两个问题。
Is it rival: does my using it leave less for you — that is rivalry.
它有竞争性吗：我用了，你能用的是不是就变少？
And is it excludable: can a non-payer be kept out — that is excludability.
它有排他性吗：不付钱的人能不能被挡在外面？
Every good lands in one of four boxes.
每件商品都会落进四个格子中的一个。
Food is rival and excludable, a private good.
食物既有竞争性又有排他性，是私人物品。
Ocean fish are rival but open to all, a common resource.
海里的鱼有竞争性却对所有人开放， 是公共资源。
A cinema seat is a club good.
电影院的座位是俱乐部物品。
A street light is neither: a public good.
路灯两者都不是：那就是公共物品。
Look at the right-hand column, where nobody who refuses to pay can be shut out.
看右边那一列，凡是不肯付钱的人都挡不住。
That one fact breaks markets two opposite ways.
这一个事实以两种相反的方式破坏市场。
If it is also non-rival, like a street light, everyone waits for a neighbour to pay.
如果它同时又没有竞争性，比如路灯， 每个人都等着邻居出钱。
Each person is a free rider, so markets under-provide it and the light is never built unless government supplies it.
人人都是搭便车的人，灯也就永远建不起来。
But if the good is rival, like fish in the sea, every boat takes all it can, and the stock is stripped bare — the tragedy of the commons.
但如果这件物品有竞争性，比如海里的鱼，每条船都尽量多捕， 鱼群被捕捞一空——这就是公地悲剧。
Government also steps in where one firm holds all the power.
在一家企业掌握全部势力的地方，政府也会介入。
This is a natural monopoly: its average cost keeps falling, so one large firm supplies it more cheaply than several small ones.
这是一家自然垄断企业：它的平均成本一直在下降， 所以一家大企业供应市场比好几家小企业更便宜。
A regulator can order price to equal marginal cost. Regulating a monopoly's price this way raises efficiency, unlike a price control in a competitive market, which just creates a shortage. But that price sits below average cost, so the firm loses money on every unit.
监管者可以要求价格等于边际成本，但那个价格低于平均成本， 企业每卖出一单位都在亏钱。
That is the regulator's dilemma.
这就是监管者的两难。
Marginal-cost pricing gives the efficient quantity but pushes a natural monopoly into a loss.
边际成本定价给出有效率的数量， 却把自然垄断推入亏损。
Average-cost pricing is the compromise: the firm just breaks even.
平均成本定价是折中：企业刚好保本。
Antitrust laws are the other tool, blocking anti-competitive mergers and collusion.
反垄断政策是另一件工具，它阻止会扼杀竞争的合并。
But when the cure costs more than the failure, that is government failure.
但当治疗的代价高过失灵本身，那就是政府失灵。
Two taxes, one market.
两种税，同一个市场。
On the left, a per-unit tax: the firm pays it on every unit, so it joins marginal cost.
左边是从量税：企业每一单位都要交， 所以它进入了边际成本。
Watch the supply curve shift up by the tax.
看供给曲线按税额向上移动。
Price rises, quantity falls, and a new deadweight loss opens.
价格上升，数量下降，新的无谓损失打开了。
On the right, a lump-sum tax: one fixed charge, whatever the firm makes.
右边是定额税：一笔固定的收费， 不管企业生产多少。
It touches neither marginal cost nor marginal benefit, so in the short run price and quantity are unchanged — only profit falls.
它既不碰边际成本，也不碰边际收益， 所以什么都不动——只有利润减少。
That is why a natural monopoly needs a lump-sum subsidy, not a per-unit one.
这就是为什么自然垄断需要定额补贴，而不是从量补贴。
Last, inequality — the income distribution a market produces.
最后是不平等。 把每个家庭从最穷到最富排好队，画出到目前为止挣到的收入份额。
Line up every household from poorest to richest, and plot the income earned so far.
如果每个人挣得一样多，你得到的就是那条笔直的平等线。
If everyone earned the same you would get the straight line of equality. Real economies sag below it; that sagging line is the Lorenz curve.
真实的经济体都垂在它下面；那条下垂的线就是洛伦兹曲线。
The deeper the sag, the more unequal the country.
垂得越深，这个国家越不平等。
The Gini coefficient turns that sag into one number: zero is total equality, one is one household owning it all.
基尼系数把这份下垂变成一个数字： 零是完全平等，一是全部收入归一个家庭。
A deeply bowed curve means a high Gini coefficient. You must read this curve, not draw it.
你要会读这条曲线，而不是把它画出来。
Where does it come from?
不平等从哪里来？
Differences in human capital — skills and education — plus inherited wealth and discrimination.
来自人力资本的差异——技能和教育—— 还有继承的财富和歧视。
The answer is progressive taxes and transfer payments — welfare and subsidies.
应对办法是税收和转移支付。
A progressive tax takes a higher percentage from higher incomes, narrowing the gap.
累进税从较高的收入中拿走更高的比例，把差距缩小。
A proportional tax takes the same percentage from everyone.
比例税对每个人抽同样的比例。
A regressive tax takes more from low incomes and widens it.
累退税从低收入中拿走更多，把差距拉大。
But redistribution can weaken the reward for working. That is the efficiency-equity trade-off: fairness against the size of the pie.
但再分配会削弱工作的回报：这是公平与蛋糕大小之间的取舍。
Four marks students give away.
四个学生常送掉的分。
First, name the failure before you draw anything: externality, public good, market power, or inequality.
第一，动笔之前先说清是哪一种失灵： 外部性、公共物品、市场势力，还是不平等。
Second, on every externality graph, mark both quantities and shade the loss between them.
第二，在每一张外部性图上， 把两个数量都标出来，并把它们之间的损失涂上阴影。
Third, size the tax to the external cost, not the whole cost of the good.
第三，税额要对准外部成本，而不是整件商品的成本。
Fourth, remember what a lump-sum charge does: it changes fixed cost only, so price and quantity stay put.
第四，记住定额收费的作用：它只改变固定成本，所以价格和数量都不动。
Get those right and this unit is yours.
把这些做对，这个单元就是你的了。