需求的價(jià)格彈性名詞解釋?zhuān)ˋlevel經(jīng)濟(jì)A）

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今天帶給大家Alevel經(jīng)濟(jì)筆記是：

第三章：Elasticities—

Cross Price Elasticity of Demand Formulae;

Cross Price Elasticity of Demand

A definition and the formula

If you understand the concept of price elasticity of demand, then it is fairly easy to grasp cross price elasticity of demand.

The issue is still how responsive demand is to a given price change, the difference here is that one is measuring the responsiveness of the quantity demanded of one good with respect to a given price change in a different good, ceteris paribus.

如果你理解了需求價(jià)格彈性的概念，那么理解需求的交叉價(jià)格彈性是相當(dāng)容易的。問(wèn)題仍然是需求對(duì)給定價(jià)格變化的響應(yīng)程度，這里的區(qū)別在于衡量一種商品的需求量相對(duì)于另一種商品的給定價(jià)格變化的響應(yīng)性，其他條件不變。

As you can see, the formula used to calculate the cross price elasticity of demand is basically the same as the one used to calculate the price elasticity of demand, except for the distinction between good A and good B:

可以看到，計(jì)算需求交叉價(jià)格彈性的公式與計(jì)算需求價(jià)格彈性的公式基本相同，除了商品A和商品B的區(qū)別：

Where:

EY = The income elasticity of demand

Δ = 'change in'

Qd = Quantity demanded

Y = Real income

Substitute, complement and independent goods

替代品、互補(bǔ)品和獨(dú)立品

The cross price elasticity of demand is useful for economists because it tells you whether two goods (A and B) are substitutes, complements or even unrelated.

Think about this example:

需求的交叉價(jià)格彈性對(duì)經(jīng)濟(jì)學(xué)家很有用，因?yàn)樗梢愿嬖V您兩種商品（A 和 B）是否是替代品、互補(bǔ)品，甚至是不相關(guān)的。想想這個(gè)例子：

Tea and coffee are substitutes.

Let's say that tea is good A and coffee is good B. If the price of coffee falls by, say, 10% ceteris paribus, then one would expect coffee to become relatively more popular at the expense of the demand for tea.

The demand for tea might fall by, say, 5%. Using the formula above, we can calculate the cross price elasticity:

茶和咖啡是替代品。假設(shè)茶是好的 A，咖啡是好的 B。如果咖啡的價(jià)格下降，比如說(shuō)，在其他條件不變的情況下下降 10%，那么人們會(huì)期望咖啡變得相對(duì)更受歡迎，但會(huì)犧牲對(duì)茶的需求。對(duì)茶的需求可能會(huì)下降 5%。使用上面的公式，我們可以計(jì)算交叉價(jià)格彈性：

Briefly, the price of coffee falls, so the demand for tea falls. This is a positive relationship, as is true for all pairs of goods that are substitutes.

If the cross price elasticity of demand is positive then the two goods in question will be substitutes.

簡(jiǎn)而言之，咖啡價(jià)格下跌，因此對(duì)茶的需求下降。這是一種正向關(guān)系，對(duì)于所有可替代的商品對(duì)都是如此。如果需求的交叉價(jià)格彈性為正，那么這兩種商品將是替代品。

Tea and sugar are complements. Sugar is a complement to a cup of tea (for some people, anyway!).

Assume that sugar is good A and tea is good B. If the price of tea fell by, say, 10% ceteris paribus, then one would expect the demand for tea to rise.

This should cause the demand for sugar to rise, although not everyone has sugar in their tea, and if they do the quantities are not exactly massive, so the rise in demand for sugar is likely to be a lot smaller than the rise in demand for tea. Let's say that the demand for sugar rises by 2%. Using the formula, we have:

茶和糖是互補(bǔ)的。糖是一杯茶的補(bǔ)充（對(duì)某些人來(lái)說(shuō)，無(wú)論如何！）。假設(shè)糖是好的 A，茶是好的 B。如果茶的價(jià)格下降，比如說(shuō)，在其他條件不變的情況下下降 10%，那么人們會(huì)預(yù)期對(duì)茶的需求會(huì)上升。這應(yīng)該會(huì)導(dǎo)致對(duì)糖的需求上升，盡管不是每個(gè)人的茶中都有糖，而且如果他們這樣做，數(shù)量也不是很大，所以對(duì)糖的需求增長(zhǎng)可能比對(duì)糖的需求增長(zhǎng)要小得多。茶。假設(shè)對(duì)糖的需求增加了 2%。使用公式，我們有：

Put briefly, the price of tea falls, so the demand for sugar rises. This is a negative relationship, as is true for all pairs of goods that are complements.

If the cross price elasticity of demand is negative then the two goods in question will be complements.

簡(jiǎn)而言之，茶葉價(jià)格下跌，因此對(duì)糖的需求增加。這是一種負(fù)關(guān)系，對(duì)于所有互補(bǔ)的商品對(duì)都是如此。如果需求的交叉價(jià)格彈性為負(fù)，那么這兩種商品將是互補(bǔ)品。

What will happen to the demand for sugar when the price of cinema admissions changes, ceteris paribus? Absolutely nothing, I should think. The two goods are completely unrelated. Using the formula:

在其他條件不變的情況下，當(dāng)電影院門(mén)票價(jià)格發(fā)生變化時(shí)，糖的需求會(huì)發(fā)生什么變化？絕對(duì)沒(méi)有，我應(yīng)該想。這兩種商品完全不相關(guān)。使用公式：

If the cross price elasticity of demand is zero then the two goods in question will be totally unrelated (or independent).

如果需求的交叉價(jià)格彈性為零，那么所討論的兩種商品將完全不相關(guān)（或獨(dú)立）。

Finally, note that the higher the value of the cross price elasticity, the stronger the relationship between the two goods in question, whether they be substitutes of complements.

The nearer the figure is to zero, the more likely that the two goods are unrelated.

最后，請(qǐng)注意交叉價(jià)格彈性的值越高，這兩種商品之間的關(guān)系越強(qiáng)，無(wú)論它們是否是互補(bǔ)品的替代品。該數(shù)字越接近于零，兩種商品不相關(guān)的可能性就越大。

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關(guān)于Alevel經(jīng)濟(jì)筆記第三章：Elasticities后續(xù)的更新計(jì)劃如下：