计量经济学ess的计算公式（AlevelAP经济高分笔记供给公式的价格弹性）

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今天带给大家Alevel经济笔记是：

第三章：Elasticities—

Price Elasticity of Supply Formulae；

Price Elasticity of Supply；

A definition and the formula

Again, the key word is responsiveness, but this time we need to find out how responsive supply is to a given price change (rather than demand).

Unsurprisingly, the formula used is very similar to the others in structure:

同样，关键词是响应性，但这次我们需要找出供应对给定价格变化（而不是需求）的响应程度。不出所料，使用的公式在结构上与其他公式非常相似：

Where:	Es = The price elasticity of supply
	Δ = 'change in'
	Qs = Quantity supplied
	P = Price

Using the formula

使用公式

I do not want to dwell on this for two reasons. First, there are far fewer questions in examinations focused on the price Elasticity of supply.

Examiners prefer demand, where one can analyse the affects on the revenues on the firm in question (see the Learn-It on the 'Price elasticity of demand').

Secondly, the way in which one uses this formula is exactly the same as the way in which one uses the formula for the price elasticity of demand.

Try the following examples to check that you agree with me.

Click on the appropriate button to reveal the answers.

出于两个原因，我不想详述这一点。首先，以供给价格弹性为重点的考试题少得多。审查员更喜欢需求，可以分析对所讨论公司的收入的影响（参见关于“需求价格弹性”的Learn-It ）。其次，这个公式的使用方式与需求价格弹性公式的使用方式完全相同。试试下面的例子来检查你是否同意我的观点。单击相应的按钮以显示答案。

The market price for apples rises from 50p per lb to 55p per lb. A greengrocer would like to increase his supply of apples at this higher price from 40lbs a day to 50lbs a day. What is the price elasticity of supply (ceteris paribus)?

苹果的市场价格从每磅 50 便士上升到每磅 55 便士。蔬菜水果商希望以这种较高的价格将他的苹果供应量从每天 40 磅增加到每天 50 磅。供给的价格弹性是多少（其他条件不变）？

The market price for Brand X lager rises from £2 a pint to £2.10 a pint. The price elasticity of supply for Brand X is 1.6. A publican would like to change his supply of Brand X in response to this price change. He currently supplies 300 pints a day. What will he supply following the price change (ceteris paribus)?

Brand X lager 的市场价格从每品脱 2 英镑上涨到每品脱 2.10 英镑。品牌 X 的供给价格弹性为 1.6。一位老板想改变他对品牌 X 的供应以响应这种价格变化。他目前每天供应 300 品脱。价格变化后他将提供什么（其他条件不变）？

Notice that the elasticities are positive.

Supply curves tend to be upward sloping, so the relationship between price and quantity supplied is nearly always positive.

Hence the value of the elasticity is nearly always positive.

The only exceptions are zero and infinity.

Zero is not strictly positive, but it isn't negative either.

请注意，弹性是正的。供给曲线倾向于向上倾斜，因此价格和供给量之间的关系几乎总是正的。因此弹性值几乎总是正的。唯一的例外是零和无穷大。零严格来说不是正数，但也不是负数。

Price Elasticity of Supply

Elastic, inelastic and unitary supply

弹性、非弹性和单一供给

These terms are used in exactly the same way as with demand elasticities. I will summarise their meanings with respect to supply in the following table:

这些术语的使用方式与需求弹性完全相同。我将在下表中总结它们在供应方面的含义：

Value of the elasticity	Price rise or cut?	What will happen to the quantity supplied?
Es = 0	Price rise	The supply curve is vertical, so supply remains the same but with a higher price.
(Perfectly inelastic)	Price cut	The supply curve is vertical, so supply remains the same but with a lower price.
0 < Es < 1	Price rise	For a given rise in price, the rise in supply will be proportionately smaller than the rise in price.
(Relatively inelastic)	Price cut	For a given fall in price, the fall in supply will be proportionately smaller than the rise in price.
Es = 1 (Unitary elasticity)	Price rise or a price cut	For a given change in price (up or down) the change in supply will be proportionately the same as the change in price.
1 < Es < ∞	Price rise	For a given rise in price, the rise in supply will be proportionately larger than the rise in price.
(Relatively elastic)	Price cut	For a given fall in price, the fall in supply will be proportionately larger than the fall in price.

Again, I have missed out the case where the elasticity is infinite.

As with demand, the curve is horizontal, implying that firms can supply as much as they want at a given price.

Another way of looking at it is that if there is a change in price then the quantity supplied will fall to zero.

同样，我错过了弹性无限的情况。与需求一样，曲线是水平的，这意味着企业可以在给定的价格下提供尽可能多的供应。另一种看待它的方式是，如果价格发生变化，那么供应量将降至零。

The diagrams

When we looked at the diagrams illustrating the elasticity of demand curves, the key point was how steep or flat the curve was (although it must be appreciated that the elasticity did change as one moved along the demand curve).

With supply curves, the issue is not so much the gradient of the curve but whether it cuts the x-axis, the y-axis or the origin.

当我们查看说明需求曲线弹性的图表时，关键点是曲线的陡峭或平坦程度（尽管必须认识到弹性确实随着需求曲线的移动而变化）。对于供给曲线，问题不在于曲线的梯度，而在于它是否切割 x 轴、y 轴或原点。

In the diagram above, S1 is quite a flat curve but S2 is fairly steep. But the gradient is not the issue.

Both curves have an elasticity of less than one because they both cut the x-axis.

The percentage change in quantity supplied has to be higher than the percentage change in price because one is working out the percentage change in quantity supplied from a higher initial figure.

在上图中，S 1是一条相当平坦的曲线，但 S 2相当陡峭。但梯度不是问题。两条曲线的弹性都小于1，因为它们都切割x 轴。供给量变化的百分比必须高于价格变化的百分比，因为人们正在从较高的初始数字计算供给量的百分比变化。

You might expect the flatter curve to be relatively elastic.

Looking at the move from point A to point B in the diagram, if the price rises from 1 to 2 (a 100% increase) this causes quantity supplied to rise from 10 to 12 (a 20% rise).

This gives an elasticity of 0.2 (20 divided by 100), which is very inelastic.

您可能期望更平坦的曲线相对有弹性。看图中从 A 点到 B 点的移动，如果价格从 1 上升到 2（增加 100%），这会导致供应量从 10 上升到 12（增加 20%）。这给出了 0.2 的弹性（20 除以 100），这是非常无弹性的。

The vertical curve S3 is perfectly inelastic in the same way that a vertical demand curve is perfectly inelastic.

垂直曲线 S 3完全缺乏弹性，就像垂直需求曲线完全缺乏弹性一样。

In the diagram above, S5 is quite a flat curve but S4 is fairly steep. Again, the gradient is not the issue.

Both curves have an elasticity of more than one because they both cut the y-axis.

The percentage change in price has to be higher than the percentage change in quantity demanded because one is working out the percentage change in price from a higher initial figure.

在上图中，S 5是一条相当平坦的曲线，但 S 4相当陡峭。同样，梯度不是问题。两条曲线的弹性都大于1，因为它们都切割y 轴。价格变化的百分比必须高于需求量的变化百分比，因为人们正在从较高的初始数字计算价格变化的百分比。

You might expect the steeper curve to be relatively inelastic.

Looking at the move from point C to point D in the diagram, if the price rises from 10 to 12 (a 20% increase) this causes quantity supplied to rise from 2 to 4 (a 100% rise).

This gives an elasticity of 2.5 (50 divided by 20), which is very elastic.

您可能会认为较陡的曲线相对缺乏弹性。看图中从 C 点到 D 点的移动，如果价格从 10 上涨到 12（上涨 20%），这会导致供应量从 2 上涨到 4（上涨 100%）。这给出了 2.5 的弹性（50 除以 20），非常有弹性。

The vertical curve S6 is perfectly elastic in the same way that a horizontal demand curve is perfectly elastic.

垂直曲线 S 6是完全弹性的，就像水平需求曲线是完全弹性的一样。

In the diagram above, all three curves go through the origin.

Again, the gradient is not the issue.

Whether the curve is steep, flattish or at an angle of 45 degrees, the percentage change in the quantity supplied will be exactly the same as the percentage change in price.

在上图中，所有三条曲线都经过原点。同样，梯度不是问题。无论曲线是陡峭、平坦还是呈 45 度角，供应量的百分比变化将与价格的百分比变化完全相同。

Look at the moves from point E to F and from point G to H.

In both cases the price increases from 20 to 24 (a 20% increase).

When moving from E to F, the quantity supplied rises from 10 to 12 (a 20% rise).

When moving from G to H the quantity supplied rises from 20 to 24 (a 20% rise. In both cases the percentage change in quantity supplied is exactly the same as the percentage change in price.

As with demand elasticities, this is known as unitary elasticity.

查看从 E 点到 F 点和从 G 点到 H 点的走势。在这两种情况下，价格都从 20 上涨到 24（上涨 20%）。当从 E 移动到 F 时，供给量从 10 上升到 12（上升 20%）。当从 G 移动到 H 时，供应量从 20 上升到 24（上升 20%。在这两种情况下，供应量的百分比变化与价格变化的百分比完全相同。与需求弹性一样，这被称为单一弹性。

The determinants of the value of the price elasticity of supply

供给价格弹性值的决定因素

As with demand, there are numerous factors that will affect the value of the price elasticity of supply.

Many of them are similar in nature to those used to explain the value of the price elasticity of demand.

与需求一样，有许多因素会影响供给价格弹性的值。其中许多在性质上与用于解释需求价格弹性值的那些相似。

Does the industry have spare capacity?

During a recession, there tends to be more spare capacity in firms and industries.

This means that firms have the ability to increase output; perhaps some of their machines are currently unused.

In these situations, firms will be able to respond quickly to a rise in the price of their product and so supply will be relatively elastic.

If the economy, or the firm in question, is close to full capacity, then they will not be able to respond so quickly to a price rise so the supply curve will be relatively inelastic.

行业有闲置产能吗？在经济衰退期间，企业和行业往往会有更多的闲置产能。这意味着企业有能力增加产量；也许他们的一些机器目前没有使用。在这些情况下，公司将能够对其产品价格的上涨做出快速反应，因此供应将相对具有弹性。如果经济体或相关企业接近满负荷生产，那么它们将无法对价格上涨做出如此迅速的反应，因此供给曲线将相对缺乏弹性。

Can the product be stored?

Some goods can be kept as stock very easily.

You have probably seen the pictures of the huge areas of parked new cars on TV whenever there is a feature about the declining car industry on the news.

If a firm has the ability to stockpile the product in question, then it can respond quickly to a rise or a fall in price by simply running down or piling up its stocks. In this case supply would be relatively elastic.

Firms that sell perishables, for example (like greengrocers), cannot store old produce, and so their ability to respond to changes in the price level is reduced.

Their supply will be relatively inelastic on this count.

产品可以储存吗？有些商品可以很容易地作为库存保存。每当新闻中有关于汽车行业衰退的报道时，您可能已经在电视上看到了停放新车的大片区域。如果一家公司有能力储存有问题的产品，那么它可以通过简单地减少或堆积其库存来快速响应价格的上涨或下跌。在这种情况下，供给会比较有弹性。例如，销售易腐烂产品的公司（如蔬菜水果商）不能储存旧产品，因此它们对价格水平变化的反应能力降低。在这方面，他们的供应相对缺乏弹性。

How long is the production process?

Factories make cars very quickly nowadays with the production lines filled with robots.

On the other hand, the length of time from the planting of the seed to the harvesting of the crop for most agricultural products is very long, relatively.

The shorter the production period the more elastic supply will be as, again, the firm in question can respond more quickly to a change in the price level.

生产过程需要多长时间？如今，工厂生产汽车的速度非常快，生产线上装满了机器人。另一方面，大多数农产品从播种到收割的时间相对来说是很长的。生产周期越短，供应的弹性就越大，同样，相关公司可以更快地对价格水平的变化做出反应。

Can the firm produce substitutes easily?

This is similar to the 'substitutes' factor in the 'determinant of the value of the elasticity of demand' section.

The difference is that we are now dealing with substitute products that a firm can produce given the materials to hand, rather than substitute choices for the consumer to buy.

Again, the magnitude of the elasticity of supply depends on the ability to respond quickly to price changes.

If a firm is making cars, but the price of cars is falling relative to the price of motorbikes, then the firm may be tempted to stop making cars and start making motorbikes.

The machines, workers and materials they have will be similar(ish!) to those required for motorbike making, so they should be able to respond quite quickly.

If a farmer wanted to transfer to the production of motorbikes, he might find it a little bit more difficult!

企业能否轻松生产替代品？这类似于“需求弹性值的决定因素”部分中的“替代”因素。不同之处在于，我们现在处理的是公司在现有材料的情况下可以生产的替代产品，而不是消费者购买的替代选择. 同样，供给弹性的大小取决于快速响应价格变化的能力。如果一家公司正在制造汽车，但汽车的价格相对于摩托车的价格正在下降，那么该公司可能会倾向于停止制造汽车并开始制造摩托车。他们拥有的机器、工人和材料将与制造摩托车所需的相似（ish！），因此他们应该能够很快做出反应。如果一个农民想转行生产摩托车，他可能会觉得有点困难！

What is the time period under consideration?

We have touched on this before.

The elasticity of supply will depend on whether the time period involved is immediate (or 'momentary'), relatively short (the 'short run') or relatively long (the 'long run').

The diagram below should help to explain:

考虑的时间段是多少？我们之前已经谈到过这一点。供给弹性取决于所涉及的时间段是即时的（或“瞬间的”）、相对较短的（“短期”）还是相对较长的（“长期”）。下图应该有助于解释：

S1 is a vertical, perfectly inelastic, supply curve.

This represents 'momentary' supply. In most industries, if a firm was asked to produce a large order immediately, it simply would not be able to do it, regardless of the price offered for the order.

Supply is perfectly inelastic in the very short run.

S 1是一条垂直的、完全无弹性的供给曲线。这代表“瞬时”供应。在大多数行业中，如果一家公司被要求立即生产大订单，它根本无法做到，无论订单的价格如何。在很短的时间内，供给是完全没有弹性的。

S2 is a fairly inelastic curve representing the short run. In the short run, a firm is able to vary some of its inputs (like labour and raw materials), but some of them will remain fixed (capital, in particular).

The firm will be able to respond to a price change, but not to any great extent.

S 2是代表短期的相当无弹性的曲线。在短期内，公司能够改变一些投入（如劳动力和原材料），但其中一些将保持不变（尤其是资本）。该公司将能够对价格变化做出反应，但幅度不大。

S3 is a relatively elastic supply curve representing the long run. In the long run, all factors of production are variable, so the firm can respond easily to a price change.

S 3是代表长期的相对弹性的供给曲线。从长远来看，所有生产要素都是可变的，因此公司可以轻松应对价格变化。

In all of the factors above, I have kept referring to a firm's ability to respond to a change in price.

It is worth asking the question at this stage: 'what would cause the price to change if one assumes that the supply curve is given and fixed?'

In the topic on 'supply and demand' we looked at shifts in demand and supply.

If we have a fixed supply curve and the price has changed, the only explanation is that the demand curve has shifted.

What I am trying to say, I suppose, is that whenever I refer to the firm's ability to respond to a change in price, I am, effectively, also referring to the firm's ability to respond to a change in demand.

在上述所有因素中，我一直提到公司应对价格变化的能力。在这个阶段值得提出一个问题：“如果假设供给曲线是给定的并且是固定的，什么会导致价格变化？” 在“供求”主题中，我们研究了供求关系的变化。如果我们有一条固定的供给曲线并且价格发生了变化，唯一的解释是需求曲线发生了移动。我想我想说的是，每当我提到公司对价格变化的反应能力时，我实际上也是指公司对需求变化的反应能力。

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关于Alevel经济笔记第三章：Elasticities后续的更新计划如下：

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