📚 Aggregate Expenditure | 总支出
In macroeconomics, aggregate expenditure is the planned total spending on domestically produced goods and services over a given period. It is central to Keynesian analysis because it explains how short-run national income and employment are determined.
在宏观经济学中，总支出是在给定时期内对国内生产的商品和服务的计划总支出。它是凯恩斯分析的核心，因为它解释了短期国民收入和就业如何被决定。
1. Defining Aggregate Expenditure | 总支出的定义
Aggregate expenditure (AE) is the total planned spending by households, firms, the government and the foreign sector on final goods and services produced within an economy during a period.
总支出（AE）是家庭、企业、政府和国外部门在一个时期内对经济体内生产的最终商品和服务的计划支出总额。
It is expressed as the sum of consumption, planned investment, government spending and net exports. The identity is shown below.
它表示为消费、计划投资、政府支出和净出口之和。其恒等式如下所示。
AE = C + I + G + (X − M)
In national accounting, actual expenditure always equals actual output because unsold goods are recorded as unplanned inventory investment. Planned aggregate expenditure, however, can differ from actual output, and this difference triggers output adjustments.
在国民核算中，实际支出始终等于实际产出，因为未售出的商品被记录为未计划存货投资。然而，计划总支出可以不同于实际产出，这一差额会引发产出调整。
2. Components of Aggregate Expenditure | 总支出的构成
The main components of aggregate expenditure are consumption by households, planned investment by firms, government spending on goods and services, and net exports.
总支出主要构成包括家庭消费、企业计划投资、政府商品和服务支出以及净出口。
| Component | 构成 |
|---|---|
| C — Consumption: household spending on durable and non-durable goods and services | 消费：家庭对耐用品、非耐用品和服务的支出 |
| I — Planned investment: business spending on capital goods and planned inventory changes | 计划投资：企业对资本品和计划存货变动的支出 |
| G — Government spending: public purchases of goods and services, excluding transfer payments | 政府支出：政府对商品和服务的公共采购，不包括转移支付 |
| X − M — Net exports: export revenue minus import spending | 净出口：出口收入减去进口支出 |
Transfer payments such as pensions are not included directly in G because they do not represent a demand for current output. They affect AE indirectly through household disposable income.
养老金等转移支付不直接计入G，因为它们不代表对当前产出的需求。它们通过家庭可支配收入间接影响总支出。
3. Consumption and the Consumption Function | 消费与消费函数
Consumption is the largest component of aggregate expenditure in most economies. Keynes assumed that consumption depends mainly on current disposable income.
消费是大多数经济中总支出最大的组成部分。凯恩斯假设消费主要取决于当前可支配收入。
The consumption function is written as:
消费函数写作：
C = a + bYd
Here, a is autonomous consumption, b is the marginal propensity to consume (MPC), and Yd is disposable income. Autonomous consumption occurs even when income is zero.
其中，a为自主消费，b为边际消费倾向（MPC），Yd为可支配收入。即使收入为零，自主消费也会发生。
The saving function is the counterpart of the consumption function:
储蓄函数是消费函数的对应函数：
S = −a + (1 − b)Yd
Since every extra unit of income is either consumed or saved, the marginal propensity to consume plus the marginal propensity to save equals one:
由于每增加一单位收入要么被消费要么被储蓄，边际消费倾向加边际储蓄倾向等于1：
MPC + MPS = 1
4. The Aggregate Expenditure Schedule | 总支出曲线
In a simple closed economy with no government, aggregate expenditure can be written as AE = A + bY, where A is autonomous expenditure and b is the MPC.
在一个没有政府的简单封闭经济中，总支出可以写作AE = A + bY，其中A为自主支出，b为MPC。
AE = A + bY
The AE schedule has a positive slope equal to the marginal propensity to consume. The vertical intercept is autonomous expenditure, which includes autonomous consumption, planned investment, government spending and autonomous net exports.
总支出曲线具有正的斜率，等于边际消费倾向。纵截距是自主支出，包括自主消费、计划投资、政府支出和自主净出口。
When taxation and imports are introduced, the slope becomes smaller because tax payments and import spending are withdrawals from the circular flow. The open-economy slope can be written as b(1 − t) − m, where t is the income tax rate and m is the marginal propensity to import.
当引入税收和进口时，斜率变小，因为税收和进口支出是从循环流量中的漏出。开放经济斜率可以写作b(1 − t) − m，其中t为所得税率，m为边际进口倾向。
5. Equilibrium in the 45° Diagram | 45度线图中的均衡
Equilibrium national income occurs where planned aggregate expenditure equals actual output. This condition is represented by the 45° line, which shows all points where Y = AE.
均衡国民收入出现在计划总支出等于实际产出的地方。这一条件由45度线表示，45度线显示了Y = AE的所有点。
Y = AE
If output is above the equilibrium level, planned spending is less than output. Firms experience unplanned increases in inventories, so they cut production. If output is below equilibrium, planned spending exceeds output, inventories fall, and firms expand production.
如果产出高于均衡水平，计划支出小于产出。企业会经历未计划存货增加，因此它们会削减生产。如果产出低于均衡水平，计划支出超过产出，存货下降，企业会扩大生产。
The adjustment process continues until unplanned inventory change is zero and output equals planned aggregate expenditure.
调整过程持续到未计划存货变动为零，产出等于计划总支出。
6. The Multiplier Process | 乘数过程
An initial increase in autonomous expenditure triggers a larger final increase in national income. This is the multiplier effect.
自主支出的初始增加会引发国民收入更大的最终增加。这就是乘数效应。
For example, if the government
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