Determination of National Income | 国民收入的决定

📚 Determination of National Income | 国民收入的决定

The determination of national income is a central topic in macroeconomics that explains how the level of output, employment and income in an economy is established. For CIE A-Level Economics, students must understand the circular flow model, the equilibrium conditions, the components of aggregate demand and aggregate supply, and the multiplier process. This article provides a comprehensive yet exam-focused guide to these concepts.

国民收入的决定是宏观经济学中的核心议题，旨在解释一个经济体的产出、就业和收入水平是如何确立的。在CIE A-Level经济考试中，学生必须理解收入循环流模型、均衡条件、总需求与总供给的构成，以及乘数过程。本文将为考生提供一份全面且紧扣考点的指南。

1. The Circular Flow of Income | 收入循环流

The circular flow of income shows the flows of money, goods and services between households and firms in an economy. In the basic two-sector model, households provide factors of production (land, labour, capital and enterprise) to firms, for which they receive factor payments: rent, wages, interest and profit. Firms use these factors to produce goods and services, which are then purchased by households. The flow of money from households to firms for goods and services is called consumption expenditure.

收入循环流展示了经济体中家庭与企业之间资金、商品和服务的流动。在基本的双部门模型中，家庭向企业提供生产要素（土地、劳动、资本和企业家才能），并因此获得要素报酬：租金、工资、利息和利润。企业利用这些要素生产商品和服务，再由家庭购买。家庭向企业购买商品和服务的货币流动称为消费支出。

At the same time, income flows in the opposite direction: firms pay households for their factor services. Therefore, there are two types of flows in the circular flow model: real flows (factors of production and goods/services) and money flows (factor payments and consumption expenditure). As long as households spend all their income, the circular flow continues at a constant level.

与此同时，收入沿相反方向流动：企业为家庭的要素服务支付报酬。因此，循环流模型中有两类流动：实物流（生产要素与商品/服务）和货币流（要素报酬与消费支出）。只要家庭将全部收入用于支出，循环流就会以恒定水平继续运行。

In reality, households do not spend all their income. Some is saved, some is paid in taxes, and some is spent on imported goods. These are withdrawals from the circular flow, which we examine in the next section.

在现实中，家庭不会将全部收入用于消费。部分收入被储蓄、缴纳税款，或用于购买进口商品。这些是从循环流中的漏出，我们将在下一节讨论。

2. Injections and Withdrawals | 注入与漏出

Withdrawals (also called leakages) are funds that leave the circular flow and reduce the amount of spending within the domestic economy. There are three types of withdrawals: savings (S), which are income not spent by households; taxation (T), which is income collected by the government; and imports (M), which are spending on goods and services produced abroad.

漏出（也称为泄流）是离开循环流并减少国内经济支出的资金。漏出有三种类型：储蓄（S），即家庭未支出的收入；税收（T），即政府征收的收入；以及进口（M），即对国外生产的商品和服务的支出。

Injections are funds that enter the circular flow from outside and increase domestic spending. There are also three types of injections: investment (I), which is spending by firms on capital goods; government spending (G), which is spending by the government on public goods and services; and exports (X), which are spending by foreign residents on domestically produced goods and services.

注入是从外部进入循环流并增加国内支出的资金。也有三种类型的注入：投资（I），即企业对资本品的支出；政府支出（G），即政府对公共商品和服务的支出；以及出口（X），即外国居民对本国生产的商品和服务的支出。

These concepts can be summarised as follows:

这些概念可总结如下：

3. Equilibrium National Income | 均衡国民收入

An economy is in equilibrium when national income is stable, meaning there is no tendency for output to rise or fall. In the circular flow model, equilibrium occurs when withdrawals equal injections:

当国民收入稳定时，经济处于均衡状态，即产出没有上升或下降的趋势。在循环流模型中，均衡发生在漏出等于注入时：

S + T + M = I + G + X

If withdrawals exceed injections, the amount of money leaving the circular flow is greater than the amount entering it. This causes national income to fall, which reduces withdrawals until equilibrium is restored. Conversely, if injections exceed withdrawals, national income rises, increasing withdrawals until the two are equal again.

如果漏出大于注入，则离开循环流的资金多于进入循环流的资金。这将导致国民收入下降，从而减少漏出，直到重新恢复均衡。反之，如果注入大于漏出，国民收入上升，漏出增加，直到两者再次相等。

Equilibrium can also be expressed in terms of aggregate demand and output. The economy is in equilibrium when aggregate demand (total planned spending) equals total output (national income). This forms the basis of the Keynesian cross model discussed in Section 6.

均衡也可以用总需求与产出来表示。当总需求（计划总支出）等于总产出（国民收入）时，经济处于均衡状态。这构成了第6节讨论的凯恩斯交叉模型的基础。

4. Aggregate Demand and Its Components | 总需求及其构成

Aggregate demand (AD) is the total planned spending on goods and services

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