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A-level经济之Oligopoly

2017-11-02 2417浏览

在A-level考试中，寡头垄断（Oligopoly）算是难点。在2016年的大纲中又新加了game theory博弈论，所以同学们要做好写关于这个知识点essay的准备。

顾名思义，寡头垄断（Oligopoly）又称寡头、寡占，一种由少数卖方（寡头）主导市场的市场状态。寡头垄断市场上的价格，通常表现为由各寡头相互协调的行为方式所决定。这种协调可以有多种形式。

oligopoly的特点有以下几点：

(i) Theory assumes profit maximisation as aim.

(ii) Theory assumes product differentiation. Products aredifferentiated by brand names. There can be product innovation.

(iii) The theory assumes that firms will keep the pricesrelatively constant because they fear changes in competitor behaviour.

(iv) Theory assumes potential competition. There may berestrictions due to barriers of entry.

(v) Theory assumes product differentiation and allows foradvertising for maximum profits.

(vi) The kinked demand curve theory does not emphasise anincrease in market share as a policy.

具体来说就是：

第一点：Higher concentration ratio。市场中由少数公司控制，统计前五家最大企业的市场份额,employment 或生产量等,超过60%为highconcentration ratio。

第二点：Interdependent of firms。每个公司之间有紧密关联，在做决策是时候会考虑到别的公司的应对方法。通常都是非价格的竞争。

第三点：High or significant barriers to entry。进入壁垒非常的高，第一是由于寡头垄断行的特殊性，比如通讯，启动资金非常的高。而且，因为现有的公司市场份额非常大，规模也非常大，所以economies of scale exploited也非常大，成本相比刚进入的公司要小非常多。因此，这些公司往往在价格上有很大优势，即使有abnormal profit。

Oligopoly有不同的种类，每个种类对于价格和生产数量的决定都非常不同。

第一种是Collusiveoligopoly。什么叫collusion？

“Collusion is a non-competitive secret or sometimes illegal agreementbetween rivals that attempts to disrupt the market's equilibrium. Collusioninvolves people or companies that would typically compete, conspiring orworking together that results in an unfair market advantage. The parties maycollectively choose to restrict the supply of a good or agree to increase itsprice to maximize profits.”

从定义中可以很明确的看出，就是串通，勾结的意思。公司为了牟利，会选择共同升高价格或者降低生产数量。但是，firms may tempt to increase output to gain bigger share of market(violate the agreement)

Collusion分成两种，explicitcollusion和tacitcollusion。

alevel资讯

Explicit collusive oligopoly where oligopolists agree tolimit competition between themselves. They may set output quotas, fix prices,limit product promotion or development, or agree not to ‘poach’ each other’smarket. Tacit collusion occurs where firmsundertake actions that are likely to minimise a competitive response, e.g.Avoiding price cutting or not attacking each other’s market.

但是，collusion要存在也必须有条件:

There are only very few firms all well known to eachother.

A strong element of trust exists between them.

They have similar production methods and cost structuresand are thus likely they want to change prices at the same time.

There is a dominant firm.

They produce similar products and can thus more easilyreach agreements on price. (product homogeneity)

There are significant barriers to entry and thereforelittle fear of disruption by new firms.

The market is stable.

另一种oligopoly的种类是Non-collusive oligopoly，跟其他市场类型不同的是，它使用的是Kinked Demand Curve Theory。

The kinked demand curve assumes that abusiness might face a dual demand curve for its product based on the likelyreactions of other firms to a change in its price or another variable.

If an oligopolist raises its price, itsrivals will not follow suit, so it will lose a lot of sales. Raising priceabove P1, firm loses market share and some total revenue. Demand is relativelyelastic.

If an oligopolist cut prices, its rivalswill follow suit and cut theirs, to prevent losing customers to the first firm.

Reducing price below P1, firm little gain in market share- other firms have followed suit. Total revenue may still fall. Demand isrelatively inelastic.

To protect and maintain their market share and that rivalfirms are unlikely to match another’s price increase but may match a pricefall.

以此可以得出，公司都不会主动去改变价格，因为无论价格上升或者下降都对他们没有好处。

所以，non-price competition就显得尤其重要，主流的有以下几点：

Advertising andpromotionSuccessful advertising cannot only shift a firm’s demand curve to theright but also it can also reduce its price elasticity of demand since itstresses the specific qualities of this firm’s productover its rivals.

BrandproliferationThe firm produces lots of brands to saturate the market and toleave no gaps for rivals.

Productimprovement and innovationProduct development are to produce a product thatwill sell well and that is different from rivals’ product (i.e. Has arelatively inelastic demand due to lack of close substitutes)

Competition ofquality of serviceFirms provide a service which is better than rivals: personalservice, late opening.

什么是博弈论（game theory）？

博弈论又被称为对策论（Game Theory）既是现代数学的一个新分支，也是运筹学的一个重要学科。博弈论考虑游戏中的个体的预测行为和实际行为，并研究它们的优化策略。生物学家使用博弈理论来理解和预测进化论的某些结果。

假设只有两个公司，两个产品，他们会如何选择？选择的结果会是怎么样？

Both firms comply

They will make monopoly profits.In order to maximiseprofits, firms restrict output to the point where their joint marginal revenuecurve equals to their joint marginal cost curve.

One firm cheats

If X cheats while Y continues to produce the agreedoutput, the result will be that X benefits from the addition sales.If Y cheatswhile X continues to product the agreed output, the result will be that Ybenefits from the addition sales.

Both firms cheat

Both firms will lose. Consumers will benefit from this.

A-level经济学中，寡头垄断企业最突出的特点是：企业之间存在着被认识到的很强的相互依存性或激烈对抗的竞争。

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