理想状态下的市场能够达到高效生产：将总剩余(total surplus)最大化。 但是在现实中的市场并非完美。在本课程中，我们将探索一系列市场存在着缺陷的情形并且理解为什么会出现这些缺陷；同时，我们会了解一些改进措施，比如反托拉斯(antitrust)政策以及其他一些政府的干预措施。 我们会选取日常中的例子——从我们每天购买和享用的货物和服务开始。我们也会在每周的练习里把理论运用到时下大事和政策研讨中。 所有的这些都会使你成为一个可以理解、分析和评价市场结果的，有学识的，有批判精神的思考者。

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来自 University of Pennsylvania 的课程

微观经济学：当市场“失灵”时

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理想状态下的市场能够达到高效生产：将总剩余(total surplus)最大化。 但是在现实中的市场并非完美。在本课程中，我们将探索一系列市场存在着缺陷的情形并且理解为什么会出现这些缺陷；同时，我们会了解一些改进措施，比如反托拉斯(antitrust)政策以及其他一些政府的干预措施。 我们会选取日常中的例子——从我们每天购买和享用的货物和服务开始。我们也会在每周的练习里把理论运用到时下大事和政策研讨中。 所有的这些都会使你成为一个可以理解、分析和评价市场结果的，有学识的，有批判精神的思考者。

从本节课中

Monopoly Continued

Monopolies come in various types: one price monopoly, natural monopoly, price discrimination and monopolistic competition. This week we will expand the basic monopoly model to cover these cases and then explore market outcomes in each case. We will also discuss how government may intervene in such cases to benefit society as a whole and increase the surplus generated by the market.

- Rebecca SteinSenior Lecturer

Economics

[MUSIC]

I'd like to present the model of a natural monopoly.

A natural monopoly is a situation where we'd naturally only want one firm.

Because one firm can provide the good at a lower cost

than two firms would be able to provide.

Good examples may be utilities where we want to have one transportation system.

Or a water system, where we really only want to have

one company providing us with water, to each of the households.

Or maybe an electric supplier, where we only want to have

one set of wires coming to each of our homes, supplying electricity.

Let's think what this implies about the cost curves.

Here is an example of a typical natural monopoly average total cost curve.

And we can see that the average total cost is falling for a very large region.

What this means is that it's cheaper to have

one firm produce the good than to divide the firm into two.

Let's work through a numeric example.

So suppose we had two firms and each of the firms were producing 10 units.

We can read off the average total cost curve and

we can see that the average cost per unit is $10.

So if we have two firms and each is producing 10 units,

we have 2 times 10 units, times the average total cost of 100, or

we get a total cost of $2000 to produce 20 units.

Now suppose we combined this firm,

these two firms into one, so that now, what would we have?

We would have one firm, and that one firm would,

instead of producing 10 units, it would be producing 20 units.

We can read off the average total cost curve,

and we can see that the average cost of production is less than 100.

Maybe it is $80 per unit.

So what is the total cost of production?

We now only have one firm.

This 1 firm is producing 20 units, each of these units cost $80 to produce,

and so the total cost is $1,600.

Now notice that in both options, we're producing 20 units.

It's just a question of how we're producing these 20 units and

clearly we can see that option two is better.

Because option two allows us to produce the same quantity at a lower cost.

So, this is an example of a natural monopoly because bigger is better.

A bigger firm is producing at a lower average cost.