📚 Absolute and Comparative Advantage | 绝对优势与比较优势
Absolute and comparative advantage are foundational concepts in international trade. They explain why countries specialise in producing certain goods and services, and why trade can make all participating countries better off even when one country is more efficient at producing everything.
绝对优势和比较优势是国际贸易的基础概念。它们解释了为什么各国会专业化生产特定的商品和服务，以及为什么即使一个国家在生产所有商品上都更有效率，贸易仍然能够使所有参与国获益。
1. Introduction to Specialisation and Trade | 专业化与贸易导论
Specialisation occurs when a country concentrates its resources on producing a limited range of goods or services. Trade then allows the country to exchange its surplus output for goods produced more efficiently elsewhere.
专业化是指一个国家将资源集中用于生产有限范围的商品或服务。贸易随后使该国能够用其剩余产出交换在其他地方生产效率更高的商品。
The theory of trade based on absolute and comparative advantage shows that the pattern of specialisation should be determined by relative opportunity costs rather than by absolute productivity alone.
基于绝对优势和比较优势的贸易理论表明，专业化的模式应当由相对机会成本决定，而不仅仅由绝对生产率决定。
2. Absolute Advantage Defined | 绝对优势的定义
A country has an absolute advantage in producing a good when it can produce more output per unit of input than another country. Equivalently, it can produce the same output using fewer resources.
当一个国家每单位投入能够生产出比另一个国家更多的产量时，该国在生产该商品上具有绝对优势。等价地说，它能够使用更少的资源生产相同的产量。
For example, if Country A can produce 20 units of food per worker per day while Country B can produce only 8 units, Country A has an absolute advantage in food production.
例如，如果 A 国每个工人每天能生产 20 单位食品，而 B 国只能生产 8 单位，那么 A 国在食品生产上具有绝对优势。
Absolute advantage is a useful starting point because it identifies which country is technically more efficient at producing a particular good. However, it does not by itself explain whether specialisation and trade will be mutually beneficial.
绝对优势是一个有用的起点，因为它识别出哪个国家在生产某种商品上技术效率更高。然而，它本身并不能解释专业化和贸易是否对双方都有利。
3. Comparative Advantage Defined | 比较优势的定义
A country has a comparative advantage in producing a good when it can produce that good at a lower opportunity cost than another country. Opportunity cost is the value of the next best alternative forgone.
当一个国家能够以比另一个国家更低的机会成本生产某种商品时，该国在生产该商品上具有比较优势。机会成本是指所放弃的次优选择的价值。
Comparative advantage is the central principle behind mutually beneficial trade. Even if one country has an absolute advantage in all goods, it cannot have a comparative advantage in everything, because opportunity costs differ across countries.
比较优势是互利贸易背后的核心原理。即使一个国家在所有商品上都具有绝对优势，它也不可能在所有商品上都拥有比较优势，因为各国之间的机会成本不同。
4. Opportunity Cost as the Basis of Comparative Advantage | 作为比较优势基础的机会成本
To identify comparative advantage, we must calculate the opportunity cost of producing one unit of each good. The formula is the amount of the other good sacrificed divided by the amount of the good gained.
要识别比较优势，我们必须计算生产每一单位商品的机会成本。公式是所放弃的另一种商品的数量除以所获得的该商品的数量。
In a two-good model, if a country uses all its resources to produce either food or clothing, the opportunity cost of food is the quantity of clothing forgone per unit of food produced.
在两种商品的模型中，如果一个国家将其全部资源用于生产食品或服装，食品的机会成本就是每生产一单位食品所放弃的服装数量。
Opportunity cost of 1 unit of food = maximum clothing output ÷ maximum food output
1 单位食品的机会成本 = 服装最大产量 ÷ 食品最大产量
5. Worked Numerical Example: Output per Worker | 数字示例：每工人产出
Consider two countries, Country A and Country B. Both can produce two goods: food and clothing. The table below shows output per worker per day.
假设有两个国家，A 国和 B 国。两国都能生产两种商品：食品和服装。下表显示了每个工人每天的产出。
| Country | Food (units per worker) | Clothing (units per worker) |
| Country A | 20 | 10 |
| Country B | 8 | 16 |
Country A has an absolute advantage in food because 20 units is greater than 8 units. Country B has an absolute advantage in clothing because 16 units is greater than 10 units.
A 国在食品上具有绝对优势，因为 20 单位大于 8 单位。B 国在服装上具有绝对优势，因为 16 单位大于 10 单位。
However, absolute advantage alone is not enough to determine the best pattern of specialisation. We must compare opportunity costs.
然而，仅凭绝对优势不足以确定最佳的专业化模式。我们必须比较机会成本。
6. Identifying Comparative Advantage Using Opportunity Cost | 利用机会成本识别比较优势
For Country A, the opportunity cost of 1 unit of food is 10 ÷ 20 = 0.5 units of clothing. The opportunity cost of 1 unit of clothing is 20 ÷ 10 = 2 units of food.
对 A 国而言，1 单位食品的机会成本是 10 ÷ 20 = 0.5 单位服装。1 单位服装的机会成本是 20 ÷ 10 = 2 单位食品。
For Country B, the opportunity cost of 1 unit of food is 16 ÷ 8 = 2 units of clothing. The opportunity cost of 1 unit of clothing is 8 ÷ 16 = 0.5 units of food.
对 B 国而言，1 单位食品的机会成本是 16 ÷ 8 = 2 单位服装。1 单位服装的机会成本是 8 ÷ 16 = 0.5 单位食品。
| Country | Opportunity cost of 1 food | Opportunity cost of 1 clothing |
| Country A | 0.5 clothing | 2 food |
| Country B | 2 clothing | 0.5 food |
Country A has the lower opportunity cost of food, so Country A has a comparative advantage in food. Country B has the lower opportunity cost of clothing, so Country B has a comparative advantage in clothing.
A 国生产食品的机会成本较低，所以 A 国在食品上具有比较优势。B 国生产服装的机会成本较低，所以 B 国在服装上具有比较优势。
Notice that each country specialises in the good for which it sacrifices less of the other good. This is the core rule for determining comparative advantage.
请注意，每个国家都应专业化生产其牺牲另一种商品更少的那种商品。这是确定比较优势的核心规则。
7. Gains from Specialisation | 专业化带来的收益
Assume that before trade, each country divides its labour equally between food and clothing. Country A produces 10 food and 5 clothing, while Country B produces 4 food and 8 clothing. Total world output is therefore 14 food and 13 clothing.
假设在贸易之前，每个国家将劳动平均分配在食品和服装之间。A 国生产 10 单位食品和 5 单位服装，B 国生产 4 单位食品和 8 单位服装。因此世界总产出为 14 单位食品和 13 单位服装。
If each country specialises according to comparative advantage, Country A devotes all its labour to food and produces 20 units, while Country B devotes all its labour to clothing and produces 16 units.
如果每个国家根据比较优势进行专业化，A 国将全部劳动用于食品生产并产出 20 单位，B 国将全部劳动用于服装生产并产出 16 单位。
| Output | Before specialisation | After specialisation | Change |
| Food | 14 | 20 | +6 |
| Clothing | 13 | 16 | +3 |
Specialisation increases total world output of both goods. This increase in output is the source of the potential gains from trade.
专业化增加了两种商品的世界总产出。这种产出的增加正是贸易潜在收益的来源。
8. Terms of Trade and the Mutual Gain Range | 贸易条件与互利区间
For trade to be mutually beneficial, the international terms of trade must lie between the two countries’ domestic opportunity costs. In this example, the opportunity cost of food is 0.5 clothing in Country A and 2 clothing in Country B.
要使贸易对双方都有利，国际贸易条件必须介于两国国内机会成本之间。在本例中，食品的机会成本在 A 国为 0.5 单位服装，在 B 国为 2 单位服装。
Therefore, the mutually beneficial terms of trade for 1 unit of food must be between 0.5 and 2 units of clothing. If 1 food trades for 1 clothing, both countries gain.
因此，1 单位食品的互利贸易条件必须介于 0.5 单位和 2 单位服装之间。如果 1 单位食品交换 1 单位服装，两国都能获益。
Country A gains because it gives up 1 food, which would have cost only 0.5 clothing at home, and receives 1 clothing in return. Country B gains because it obtains 1 food by giving up 1 clothing, while producing food domestically would cost 2 clothing per unit.
A 国获益是因为它放弃 1 单位食品，而该食品在国内仅值 0.5 单位服装，却在交换中获得 1 单位服装。B 国获益是因为它用 1 单位服装换得 1 单位食品，而在国内生产 1 单位食品需要放弃 2 单位服装。
If the terms of trade are outside this range, one country would be better off producing the good domestically, so voluntary trade would not occur.
如果贸易条件超出这个区间，其中一个国家就会认为在国内生产该商品更有利，因而自愿贸易不会发生。
9. Absolute vs Comparative Advantage: Key Distinction | 绝对优势与比较优势的关键区别
Absolute advantage refers to producing more output with the same inputs. Comparative advantage refers to producing at a lower opportunity cost. A country can have an absolute advantage in both goods but still benefit from trade by specialising in the good where its relative efficiency is greatest.
绝对优势是指用相同的投入生产更多的产量。比较优势是指以更低的机会成本进行生产。一个国家可能在两种商品上都具有绝对优势，但通过专业化生产其相对效率最高的商品，它仍然能够从贸易中获益。
For example, if Country A can produce 20 food or 16 clothing while Country B can produce 10 food or 12 clothing, Country A has an absolute advantage in both goods. However, Country A’s opportunity cost of food is 0.8 clothing compared with Country B’s 1.2 clothing, so Country A has a comparative advantage only in food. Country B has a comparative advantage in clothing despite having an absolute disadvantage in both goods.
例如，如果 A 国能生产 20 单位食品或 16 单位服装，而 B 国能生产 10 单位食品或 12 单位服装，那么 A 国在两种商品上都具有绝对优势。然而，A 国食品的机会成本为 0.8 单位服装，而 B 国为 1.2 单位服装，所以 A 国仅在食品上具有比较优势。B 国尽管在两种商品上都处于绝对劣势，却在服装上具有比较优势。
This insight, first developed by David Ricardo, shows that trade does not require absolute efficiency. It requires differences in opportunity costs.
这一由大卫·李嘉图首先提出的见解表明，贸易并不要求绝对效率。贸易只需要机会成本存在差异。
10. Assumptions of the Model | 模型的假设条件
The basic model of absolute and comparative advantage rests on several simplifying assumptions. Relaxing these assumptions can reduce or change the predicted gains from trade.
绝对优势和比较优势的基本模型建立在若干简化假设之上。放宽这些假设可能会减少或改变贸易收益的预测结果。
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There are only two countries and two goods.
只有两个国家和两种商品。
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Labour is the only factor of production and is perfectly mobile between industries within a country.
劳动是唯一的生产要素，并且在一国内部不同行业之间可以完全自由流动。
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There are constant returns to scale, meaning output per worker does not change as production expands.
规模报酬不变，也就是说随着生产扩大，每工人的产出不会改变。
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No transport costs, trade barriers, or exchange rate complications are present.
不存在运输成本、贸易壁垒或汇率
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