AS经济：C2 Elasticities

对于A-level经济中AS阶段，我们在前面介绍过C1 Basic Economic Problems和C2 Demand and Supply，今天，锦秋小编将继续前面的内容，为大家详细介绍一下AS经济第二章第二部分的知识点：弹性，希望对大家复习能够有所帮助。

AS经济第二章第二部分的知识点：弹性。

AS的经济Essay，10个考生里有9个会写弹性，大家一起来复习一下吧。

弹性一共有4个知识点：

PED

XED

YED

PES

【敲黑板】对于所有的弹性，在分析各自的作用之前，请务必记住他们的定义和计算公式！

3.1 Price Elasticity of Demand (PED)

Frequently asked topics

Explain elastic/inelastic PED

Explain factors affect PED

Explain implications of PED for a producer

Discuss how producer could change PED

Explain implications of PED for the government

PED有以下五种类型的考题

•解释elastic/inelastic demand （多出现在data和a问）

•分析PED对企业家的启示（多出现在b问，会和XED,YED进行比较）

•分析企业家如何改变PED（单独的知识点，出现在b问）

•分析PED对政府的启示（多出现在indirect tax）

•在别的知识点中运用PED（consumer surplus, maximum price, indirect tax, subsidy, exchange rate）

但凡有价格或者数量的变化，大家一定要考虑PED对结果的影响，这是CAIE的重要考查部分，同学们必须要掌握。

Sample essays

16S2 Explain the meaning of ‘price elasticity of demand’ and, using examples, outline the factors that would cause the demand for a good to be relatively price-elastic. 

16S2 Discuss why entrepreneurs might want to change the price elasticity of demand for their products and consider the extent to which this is achievable. 

17S2 Discuss which measure of the different types of elasticity of demand is most useful for a business when setting the price for its product. 

16W2 Discuss how habit-forming demerit goods and goods with lots of substitutes are each likely to respond to price rises, and consider the extent to which knowledge of their likely response would be useful to government policymakers. 

3.2 Income Elasticity of Demand (YED)

Frequently asked topics

Explain normal goods, inferior goods and luxury goods.

Explain implications of YED for a producer

Explain implications of YED for the government

YED出现的次数较少，对商品的分类和对企业家的启示是常见的考点。

Sample essays

15S3 With the help of diagrams, explain how economists use the concept of income elasticity of demand to distinguish between inferior goods and necessity goods. 

17S2 Discuss which measure of the different types of elasticity of demand is most useful for a business when setting the price for its product. 

17W3 Discuss if it is more useful for governments to have knowledge of the price elasticity of demand or the income elasticity of demand for certain products. 

3.3 Cross Elasticity of Demand (XED)

Frequently asked topics

Define XED and explain substitutes and complements

Explain implications of XED for a producer

Explain implications of XED for the government

XED经常和factors affecting demand一起出现，这里对企业家的启示有一个重要的evaluation：只有close substitues/complements才对企业家做决策有影响，weak substitutes/complements几乎不影响企业家做决策。

注意：对于unrelated goods, XED=0

Sample essays

13S3 Explain, using economic analysis, how economists decide whether goods are substitutes or complementary goods. 

18S1 Discuss the extent to which knowledge of a product’s cross-elasticity of demand is likely to be important to a firm supplying that product. 

3.4 Price Elasticity of Supply (PES)

Frequently asked topics

Explain elastic/inelastic PES

Explain factors affecting PES

Discuss how business could increase PES

Discuss how government could increase PES

大家都不喜欢的知识点，毕竟我们都只是消费者而不是生产商。然而作为考试的独立知识点，送分的部分请大家牢记。

• 解释elastic/inelastic supply（多出现在data和a问）

• 分析企业家如何改变PES

• 分析政府如何改变PES

当价格上升时，每个企业家都试图多生产东西来进行销售，然而这不是一定能成功的。同学们需要了解增加PES的方法，诸如提高科技水平，增加生产效率，缩短生产周期，或者增加库存。

Sample essays

15S1 Explain two factors that are likely to make the supply of a product relatively price inelastic. 

16S2 Discuss the policies that a government might adopt to increase the price elasticity of supply of agricultural goods in an economy and consider which policy is likely to be most effective. 

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