本文来源于：CrazyALEVEL

ID：CrazyAlevel

▎Cross elasticity of demand的定义为：

It measures the responsiveness of quantity demanded of a product A when there is a change in the price of a related product B。

也就是说，

当product B的价格发生变化时，

将会对product A的需求数量造成多大的影响。

▎计算公式为: 

% Of change in quantity demanded of product A / % of change in the price of a related product B。

这里XED的value分为两种情况讨论，

一种是相互为Complements的products，

比如CD player和CD。

When the price of CD player decreases, 

The quantity demanded for CD player and CD both increase；

When the price of CD player increases, 

The quantity demanded for CDplayer and CD both decrease.

因为互为补足物的商品，

如果其中一件商品的价格上涨，

两者的需求数量将会同时下跌，

反之亦然。

所以，Complements的XED value

一定会是Negative的。

另一种是相互为Substitutes的products，

比如Apple juice和orange juice。

When the price of apple juice increases, 

The quantitydemanded for it will decrease, 

And the quantity demanded for the relatively cheaper orange juice will increase; 

When the price of apple juice decreases,

The quantity demanded for it will increase,

And the quantity demanded for the relatively more expensive

Orange juice will decrease. 

互为替代品的商品，

如果一种商品的价格上涨，

另一种商品的价格将会变得相对便宜，

而相对便宜的商品的需求数量将会上涨，

另一个则会降低。

所以，Substitutes的XED value一定会是positive的。

综上所述，

通过XED value的正负号，

我们也可以得知两个Products之间的关系了。

同时，根据XED value的绝对值大小，

又可以将其分成四类。

（以下数字全部为Assumption）

(1)  XED=-3 (Elastic)

Two products are close compliments,

Such as: CD playerand CD.

(2)  XED=-0.2 (Inelastic)

Two products are distant compliments, 

Such as red wine and cheese.

(3)  XED=2.6 (Elastic)

  Two products are close substitutes, 

Such as pepsi and coke.

(4)  XED=0.3 (Inelastic)

Two products are distant substitutes, 

Such as mineralwater and beer.

According to the extent(absolute value) of XED, 

How closely the two products are related can be determined.

以上就是这次XED精讲的内容了，

在将YED讲解完之后，

同学们可以好好整理一下PED，XED和YED

这三个Elasticities的内容。