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THE DEMAND SIDE  需求侧

1.1 OVERVIEW 1.1 概述

In the late 2000s, households and firms across the world cut back their spending and the global economy went into recession. There is little disagreement among economists that the dramatic fall in global GDP in 2008-09, which is now known as the global financial crisis, was a negative shock to aggregate demand. The Covid-19 pandemic led to a much larger contraction of global economic activity in the first half of 2020 than had occurred during the financial crisis. A combination of government mandated lock-downs of businesses and travel, and decisions by citizens to reduce their face-to-face interactions produced a collapse in demand for goods and services.
在 2000 年代末，全球的家庭和企业减少了支出，全球经济陷入衰退。经济学家们几乎没有分歧，认为 2008-09 年全球 GDP 的剧烈下降，即现在所称的全球金融危机，是对总需求的负面冲击。新冠疫情导致 2020 年上半年全球经济活动的收缩远远超过金融危机期间的情况。政府强制实施的商业和旅行封锁，以及公民减少面对面互动的决定，导致了对商品和服务需求的崩溃。
This chapter begins the task of building a macroeconomic model with the demand side of the economy, which concerns the spending decisions of households, firms and government. As we shall see in Chapter 2, the supply side refers to the production activities in the economy. Dramatic changes in aggregate demand-that is, spending in the economy as a whole-as occurred in 2020 or in 2008-09 are unusual. In more normal times, shifts in aggregate spending decisions are the main sources of the irregular fluctuations from recession to boom that form the business cycle.
本章开始构建一个宏观经济模型，侧重于经济的需求侧，涉及家庭、企业和政府的支出决策。正如我们将在第二章中看到的，供给侧指的是经济中的生产活动。2020 年或 2008-09 年发生的总需求剧烈变化——即整个经济的支出——是非常不寻常的。在更正常的时期，总支出决策的变化是导致经济周期中从衰退到繁荣的不规则波动的主要来源。
If a period of depressed spending is forecast, there is much discussion in the financial media about whether the central bank will intervene and offset the likely recession by loosening monetary policy, for example, by cutting the interest rate. The central bank would cut the interest rate because it expects this to encourage spending and help return the economy to stability. Similarly, if a boom in spending were forecast, the central bank would try to dampen it down by raising the interest rate. As well as the central bank, the government also needs to know how spending patterns are likely to evolve and affect output. A recession will depress tax revenue and increase spending on unemployment benefits. Forecasting patterns of spending is therefore a priority, not only for businesses, but also for the monetary and fiscal policy makers.
如果预测到消费支出将出现一段时间的低迷，金融媒体上会有很多讨论，关于中央银行是否会干预，通过放松货币政策来抵消可能的经济衰退，例如，降低利率。中央银行会降低利率，因为它预计这将鼓励消费支出，并帮助经济恢复稳定。同样，如果预测到消费支出将出现繁荣，中央银行会试图通过提高利率来抑制这种情况。除了中央银行，政府也需要了解消费模式可能如何演变并影响产出。经济衰退将压低税收收入，并增加失业救济支出。因此，预测消费模式是一个优先事项，不仅对企业而言，对货币和财政政策制定者也是如此。

Aggregate demand and spending decisions
总需求和支出决策

In this chapter, we focus on what lies behind the spending decisions in the economy and how they influence the level of economic activity. By the level of activity, we mean output or income. When output changes, employment also changes. For example, when output rises, more workers or longer hours are needed to produce the higher level of output. With more hours worked, the wage bill is larger and with higher sales, total profits are higher. This is why changes in economic activity are thought of as both changes in output and in income (i.e. wages and profits). When we think of a real-world
在本章中，我们关注经济中支出决策背后的因素以及它们如何影响经济活动水平。我们所说的活动水平是指产出或收入。当产出变化时，就业也会发生变化。例如，当产出上升时，需要更多的工人或更长的工作时间来生产更高水平的产出。随着工作时间的增加，工资支出也会增加，而随着销售额的提高，总利润也会增加。这就是为什么经济活动的变化被视为产出和收入（即工资和利润）的变化。当我们考虑现实世界时

economy, output is normally growing and recessions and booms produce fluctuations around a trend growth rate. However, we will often simplify by working with levels of output rather than its rate of growth.
经济中，产出通常在增长，衰退和繁荣会导致围绕趋势增长率的波动。然而，我们通常会通过关注产出水平而不是其增长率来简化分析。
Spending decisions are complex and forward-looking. For consumers they involve questions like ‘how do I allocate my spending over time given my current income and wealth, and how I expect my income to evolve in the future?’. Firms make decisions to purchase machinery and equipment and to build new premises based on a business plan that includes forecasts about how input costs and demand for their products will evolve over time. The government must also forecast demographic trends when making plans for building new schools and hospitals.
支出决策是复杂且具有前瞻性的。对于消费者来说，这涉及到诸如“在考虑到我当前的收入和财富，以及我对未来收入变化的预期时，我该如何分配我的支出？”的问题。企业根据商业计划做出购买机械设备和建设新场所的决策，该计划包括对输入成本和产品需求随时间变化的预测。政府在制定新学校和医院建设计划时，也必须预测人口趋势。
Decisions about spending by the entities that make up the economy-firms, families and government bodies-lie behind the demand side of the economy. Macroeconomics is concerned with the aggregate sum of spending decisions of these groups, and the consequences of those decisions for economy-wide outcomes such as the rate of unemployment or inflation. Household spending decisions add up to aggregate consumption, C; firms’ investment decisions add up to aggregate investment, I (note that I refers to spending on machinery, equipment and new houses and other buildings); and government spending on different goods and services adds up to a single number, G. Including the purchase of new business premises as part of investment highlights the difference between on the one hand, aggregate demand, which refers to spending on goods and services and on the other hand, the purchase of assets such as company shares or second-hand property. Buying a second-hand factory building does not contribute to aggregate demand. It is the transfer of the ownership of an asset from one business to another. In contrast, the sale of new business premises reflects the goods and services used in its construction and sale.
关于经济中各个实体（企业、家庭和政府机构）支出的决策构成了经济的需求侧。宏观经济学关注这些群体支出决策的总和，以及这些决策对经济整体结果（如失业率或通货膨胀）的影响。家庭的支出决策汇总为总消费 C；企业的投资决策汇总为总投资 I（注意，I 指的是对机械、设备、新房和其他建筑的支出）；政府在不同商品和服务上的支出汇总为一个数字 G。将新商业场所的购买视为投资的一部分，突显了总需求与资产购买之间的区别，后者包括公司股票或二手房产的购买。购买二手工厂建筑并不贡献于总需求。这是资产从一个企业转移到另一个企业的所有权转移。 与此相反，新商业场所的销售反映了其建设和销售中使用的商品和服务。
Although the first chapters in the book concentrate on a closed economy (a single nation without links with others) as noted above, in the fuller model (set out in Chapters 11 and 12) the demand side includes foreign spending on home goods and services, exports ( X ), and domestic spending on foreign goods and services, imports ( M ) ( M ) (M)(\mathrm{M}). Aggregate demand is real expenditure on goods and services produced in the home economy. This can be summarized by an equation relating real expenditure, which is called y D y D y^(D)y^{\mathrm{D}}, to its individual components:
尽管本书的前几章集中于封闭经济（一个没有与其他国家联系的单一国家），如上所述，在更完整的模型（在第 11 章和第 12 章中阐述）中，需求侧包括对本国商品和服务的外国支出、出口（X）以及对外国商品和服务的国内支出、进口 ( M ) ( M ) (M)(\mathrm{M}) 。总需求是对本国经济中生产的商品和服务的实际支出。这可以通过一个方程来总结，该方程将实际支出（称为 y D y D y^(D)y^{\mathrm{D}} ）与其各个组成部分联系起来：
y D = C + I + G + ( X − M ) , (aggregate demand) y D = C + I + G + ( X − M ) ,  (aggregate demand)  y^(D)=C+I+G+(X-M),quad" (aggregate demand) "y^{D}=C+I+G+(X-M), \quad \text { (aggregate demand) }
where we add to the trio of C , I C , I C,I\mathrm{C}, \mathrm{I} and G , the expenditure of foreigners on home output, X and subtract the spending of home agents on output produced abroad, M .
我们在 C , I C , I C,I\mathrm{C}, \mathrm{I} 和 G 的三重奏中增加外国对国内产出的支出 X，并减去国内代理对国外生产的产出的支出 M。

Aggregate demand and government policy
总需求与政府政策

Two of the major tools of macroeconomic policy, monetary and fiscal policy, work by influencing different elements on the demand side. Policy makers worry about fluctuations in aggregate demand because they affect household wellbeing via unemployment and inflation.
宏观经济政策的两个主要工具，货币政策和财政政策，通过影响需求侧的不同要素来发挥作用。政策制定者担心总需求的波动，因为它们通过失业和通货膨胀影响家庭福祉。
Monetary policy seeks to stabilize aggregate demand by changing interest rates, which affect the investment decisions of firms and the purchase of new houses and
货币政策旨在通过改变利率来稳定总需求，这会影响企业的投资决策和新房的购买
durable goods like new cars and furniture by households. A rise in the interest rate increases the cost of financing investment projects, and projects that would have gone ahead with lower interest rates are postponed or cancelled. Monetary policy also has indirect effects because the interest rate affects incentives to save and therefore shifts spending decisions over time. For example, by making new borrowing more expensive and increasing the return on saving, a higher interest rate will encourage households to postpone consumption.
耐用消费品，如新车和家具，由家庭购买。利率上升会增加投资项目的融资成本，而本来在较低利率下会进行的项目则被推迟或取消。货币政策也有间接影响，因为利率影响储蓄的激励，从而改变消费决策的时间。例如，通过使新借款变得更昂贵并提高储蓄的回报，较高的利率将鼓励家庭推迟消费。
Through changes in government spending on goods and services (G), fiscal policy affects aggregate demand directly. Fiscal policy can also be used to affect demand indirectly through its influence on household incomes and through that channel, on household spending. Changes in taxation and in the transfers made by the government to households in the form of pensions, disability and unemployment benefits feed through into the spending decisions of households, i.e. into C , to affect aggregate demand.
通过政府对商品和服务（G）的支出变化，财政政策直接影响总需求。财政政策还可以通过对家庭收入的影响以及通过这一渠道对家庭支出的影响，间接影响需求。税收变化以及政府以养老金、残疾和失业救济金形式向家庭转移的资金，会影响家庭的消费决策，即影响 C，从而影响总需求。
An important reason to study the demand side is to construct a model of the transmission mechanism by which monetary and fiscal policy, via the spending decisions of households, firms and the government, affect the economy. Before explaining the first building block of the macro model, which is the IS curve, we provide some facts about the demand side.
研究需求侧的一个重要原因是构建一个传导机制模型，通过家庭、企业和政府的支出决策，货币和财政政策如何影响经济。在解释宏观模型的第一个构建块，即 IS 曲线之前，我们提供一些关于需求侧的事实。

1.1.1 Facts about the demand side and business cycles
1.1.1 关于需求侧和商业周期的事实

Shares of GDP 国内生产总值的份额

Table 1.1 sets out the average composition of gross domestic product (GDP) in five major economies for the period between the financial crisis and the pandemic, from 2010 to 2018. GDP is the national accounts measure of national output. We discuss the calculation of GDP in the next subsection. Table 1.1 shows that consumption makes up the largest proportion of GDP in all the economies with the exception of China. In particular, the importance of consumption in GDP ranges from 37% in China to 68% in the US. A large part of this cross-country variation can be explained by differences in the contribution of investment. For example, an exceptionally high proportion of Chinese GDP arises from investment spending; the UK’s share is low. The table also
表 1.1 列出了 2010 年至 2018 年金融危机与疫情之间五大主要经济体的国内生产总值（GDP）平均构成。GDP 是国家账户衡量国家产出的指标。我们将在下一小节讨论 GDP 的计算。表 1.1 显示，消费在所有经济体中占 GDP 的最大比例，唯独中国例外。特别是，消费在 GDP 中的重要性在中国为 37%，在美国为 68%。这种跨国差异的很大一部分可以用投资贡献的差异来解释。例如，中国 GDP 中异常高的比例来自投资支出；而英国的比例则较低。表格还显示
Consumption 消费
 投资包括政府。
Investment
incl. gov.
Investment incl. gov.| Investment | | :--- | | incl. gov. |

政府消费支出
Government
cons. spending
Government cons. spending| Government | | :--- | | cons. spending |
 Net exports 净出口
China 中国 36.7 44.9 15.9 2.4
Germany 德国 53.6 20.5 19.6 6.3
Japan 日本 57.3 23.2 19.9 -0.4
United Kingdom 英国 64.7 16.7 19.9 -1.4
United States 美国 67.9 20.2 15.0 -3.1
Consumption "Investment incl. gov." "Government cons. spending" Net exports China 36.7 44.9 15.9 2.4 Germany 53.6 20.5 19.6 6.3 Japan 57.3 23.2 19.9 -0.4 United Kingdom 64.7 16.7 19.9 -1.4 United States 67.9 20.2 15.0 -3.1| | Consumption | Investment <br> incl. gov. | Government <br> cons. spending | Net exports | | :--- | :---: | :---: | :---: | :---: | | China | 36.7 | 44.9 | 15.9 | 2.4 | | Germany | 53.6 | 20.5 | 19.6 | 6.3 | | Japan | 57.3 | 23.2 | 19.9 | -0.4 | | United Kingdom | 64.7 | 16.7 | 19.9 | -1.4 | | United States | 67.9 | 20.2 | 15.0 | -3.1 |
Table 1.1 Shares of GDP (in %), current prices, average 2010-18.
表 1.1 国内生产总值（GDP）份额（%），现行价格，2010-2018 年平均。
Note: GDP in current prices is a measure of nominal GDP; shares might not add up to 100% due to statistical discrepancies.
注意：当前价格的 GDP 是名义 GDP 的一个衡量标准；由于统计差异，份额可能无法加总到 100%。
Source: OECD National Accounts (data accessed July 2020).
来源：经济合作与发展组织国家账户（数据访问于 2020 年 7 月）。
highlights the variation across countries in the contribution to GDP from net exports. On average, between 2010 and 2018, the US, the UK and Japan ran trade deficits with imports in excess of exports, whereas Germany and China were in trade surplus (see Chapter 12 for further discussion and definitions).
强调了各国在净出口对 GDP 贡献方面的差异。2010 年至 2018 年间，美国、英国和日本的贸易出现赤字，进口超过出口，而德国和中国则处于贸易顺差状态（详见第 12 章以获取更多讨论和定义）。
The upper panel of Figure 1.1 shows how the shares of consumption, investment and government spending in GDP changed over time for the UK from 1948 to 2019. From 1948 until the end of the 1960s the share of consumption falls and is mirrored by a rise in the share of investment. The share of investment peaks in 1989, falls sharply in the
图 1.1 的上半部分显示了 1948 年至 2019 年间，英国消费、投资和政府支出在 GDP 中所占份额随时间的变化。从 1948 年到 1960 年代末，消费的份额下降，而投资的份额则相应上升。投资的份额在 1989 年达到峰值，随后急剧下降。
Figure 1.1 Components of GDP in the UK: as a percentage of GDP between 1948 and 2019 (upper panel) and volatility of growth rates between 1958 Q3 and 2017 Q3 (lower panel).
图 1.1 英国 GDP 的组成部分：1948 年至 2019 年间占 GDP 的百分比（上图）以及 1958 年第三季度至 2017 年第三季度的增长率波动性（下图）。
Note: Volatility has been calculated as the standard deviation of the GDP growth rate over a rolling 21-quarter period. The upper graph uses data from the series ‘Gross Domestic Product by category of expenditure, current prices’ and the lower graph uses data from the series ‘Gross Domestic Product by category of expenditure, chained volume measures’.
注意：波动性是通过对 21 个季度滚动期间的 GDP 增长率计算标准差得出的。上图使用的是“按支出类别划分的国内生产总值（现价）”系列的数据，下图使用的是“按支出类别划分的国内生产总值（链式量度）”系列的数据。
Source: UK Office for National Statistics (data accessed July 2020).
来源：英国国家统计局（数据访问于 2020 年 7 月）。
financial crisis and recovers only weakly thereafter. The government’s consumption spending increases sharply in the crisis but then declines as austerity policies were introduced from 2010.
金融危机后仅微弱复苏。政府的消费支出在危机中急剧增加，但在 2010 年实施紧缩政策后则下降。

National accounts 国民账户

The national accounts are used to measure the output of an economy. The most commonly used measure for calculating national output is gross domestic product, or GDP. GDP can be measured in three different ways. All three equations for calculating GDP are identities, which means that because of the way the variables are defined, the left-hand side must always equal the right-hand side. This special feature of an identity is signalled by the use of the equals sign with three bars.
国民账户用于衡量一个经济体的产出。计算国民产出的最常用指标是国内生产总值，或称 GDP。GDP 可以通过三种不同的方式进行测量。计算 GDP 的这三种方程都是恒等式，这意味着由于变量的定义方式，左侧总是等于右侧。恒等式的这一特殊特征通过使用三条横线的等号来表示。
First, is the expenditure method, which is the one we use in the model of the demand side. This method measures GDP as the total expenditure on the economy’s output of goods and services:
首先是支出法，这是我们在需求侧模型中使用的方法。该方法将 GDP 衡量为对经济产出商品和服务的总支出：
y ≡ C + I + G + ( X − M ) y ≡ C + I + G + ( X − M ) y-=C+I+G+(X-M)y \equiv C+I+G+(X-M)
(GDP identity, expenditure method)
（GDP 恒等式，支出法）
where y ≡ y ≡ y-=\mathrm{y} \equiv output (or GDP), C ≡ C ≡ C-=\mathrm{C} \equiv consumption, I ≡ I ≡ I-=\mathrm{I} \equiv investment (including changes in stocks of raw materials and finished goods), G ≡ G ≡ G-=G \equiv government spending and ( X − M X − M X-MX-M ) ≡ ≡ -=\equiv net exports. This is an identity, as it simply breaks down GDP into its constituent components. A fall in one of the components on the right-hand side, for example consumption, will therefore always result in an equivalent reduction in measured GDP on the left-hand side.
其中 y ≡ y ≡ y-=\mathrm{y} \equiv 输出（或 GDP）， C ≡ C ≡ C-=\mathrm{C} \equiv 消费， I ≡ I ≡ I-=\mathrm{I} \equiv 投资（包括原材料和成品库存的变化）， G ≡ G ≡ G-=G \equiv 政府支出和（ X − M X − M X-MX-M ） ≡ ≡ -=\equiv 净出口。这是一个恒等式，因为它只是将 GDP 分解为其组成部分。右侧某个组成部分的下降，例如消费，必然会导致左侧测量的 GDP 相应减少。
When a new house is bought, just like a new piece of machinery, this is an investment decision-the house provides a flow of services to the household over many yearsand is included in the national accounts under the term, I. The house and the piece of machinery form part of the economy’s capital stock. National accountants have to make many tricky classification decisions: although households buy a variety of durable goods that provide services over many years, by convention it is only housing that is considered as investment in the national accounts. Cars and furniture, for example, are treated in the national accounts as consumption.
当购买一栋新房子时，就像购买一台新机器一样，这是一项投资决策——房子在许多年内为家庭提供服务，并在国家账户中被归类为 I。房子和机器都是经济资本存量的一部分。国家会计师必须做出许多棘手的分类决策：尽管家庭购买各种耐用消费品，这些商品在许多年内提供服务，但根据惯例，只有住房被视为国家账户中的投资。例如，汽车和家具在国家账户中被视为消费。
It is important to recall that only government spending on goods and services is part of aggregate demand; G does not include government expenditure on transfers (e.g. pensions or social security payments). When the recipients of transfers spend their income from benefits or pensions, this is then recorded as consumption.
重要的是要记住，只有政府对商品和服务的支出才是总需求的一部分；G 不包括政府对转移支付（例如养老金或社会保障支付）的支出。当转移支付的接受者用他们的福利或养老金收入进行消费时，这被记录为消费。
The expenditure method only includes final goods. For example, during the production process, firms buy raw materials and intermediate goods to make their final goods. The only purchases that are counted in GDP are when the firm sells the finished goods to the consumer. This avoids any double counting. In this way, GDP captures only the value added created in the economy. This leads onto the second approach for calculating GDP; the value added method. This method measures GDP as the value added created in all sectors of the economy, such that:
支出法仅包括最终商品。例如，在生产过程中，企业购买原材料和中间商品以制造最终商品。计入 GDP 的唯一购买是企业将成品出售给消费者时。这避免了任何重复计算。通过这种方式，GDP 仅捕捉到经济中创造的附加值。这引出了计算 GDP 的第二种方法：附加值法。该方法将 GDP 衡量为经济各个部门创造的附加值，具体如下：
y ≡ value of output sold - cost of raw materials and intermediate goods y ≡  value of output sold - cost of raw materials and intermediate goods  y-=" value of output sold - cost of raw materials and intermediate goods "y \equiv \text { value of output sold - cost of raw materials and intermediate goods }
(GDP identity, value added method)
（GDP 恒等式，增加值法）
The third and final approach for calculating GDP is the income method. This method measures GDP as the total income of all agents in the economy, such that:
计算 GDP 的第三种也是最后一种方法是收入法。该方法将 GDP 视为经济中所有经济主体的总收入，具体如下：
y ≡ y ≡ y-=y \equiv salaries of workers + profits of the owners of capital (GDP identity, income method)
y ≡ y ≡ y-=y \equiv 工资 + 资本所有者的利润（GDP 恒等式，收入法）
The three methods of calculating GDP are all identities and each holds at each point in time. It makes intuitive sense that the total income in the economy is equal to the total expenditure on goods and services produced at home, because for every transaction there is both a buyer and a seller. What is expenditure for the buyer is income to the seller. In practice, however, GDP calculated using the three methods may differ. This is a matter of measurement error, which can arise for several reasons. Measurement error may be more serious for one rather than another of the three methods. For example, tax evasion or the existence of a substantial black market are likely to produce a greater problem of underestimation of GDP when measured by incomes than for the other methods. If the underlying components could be measured completely accurately, then each of the three approaches would yield exactly the same estimate of GDP.
计算 GDP 的三种方法都是恒等式，并且在每个时间点上都成立。经济中的总收入等于国内生产的商品和服务的总支出，这在直观上是合理的，因为每一笔交易都有买方和卖方。对买方而言的支出对卖方而言就是收入。然而，在实践中，使用三种方法计算的 GDP 可能会有所不同。这是一个测量误差的问题，可能由于多种原因而产生。测量误差在三种方法中可能对某一种方法更为严重。例如，逃税或存在大量黑市在通过收入测量 GDP 时，可能会导致更严重的低估问题，而对其他方法的影响则较小。如果基础组成部分能够被完全准确地测量，那么这三种方法将会得出完全相同的 GDP 估算值。

Relative volatility 相对挥发性

The lower panel of Figure 1.1 shows the relative volatility of growth rates for the three components of aggregate demand: a higher standard deviation means higher volatility. We can see that investment is much more volatile than consumption and government spending: the line showing the standard deviation for investment lies above that for consumption and government spending. Investment depends on expected post-tax profits and is very dependent on how optimistic firms are, so it tends to flourish in boom periods and collapse in recessions, making it more volatile than the other components of GDP, or GDP itself. In addition to this, investment can also be postponed in recessions, whereas government current spending and consumption cannot be as easily delayed. For example, a household still has to spend money on food and drink in a recession, whereas a firm may choose to wait until the economy has recovered before it undertakes investment. We shall also see-in Section 1.2.6that fixed investment decisions are often bunched, further accounting for the greater volatility of investment.
图 1.1 的下半部分显示了总需求三个组成部分的增长率相对波动性：标准差越大，波动性越高。我们可以看到，投资的波动性远高于消费和政府支出：投资的标准差线位于消费和政府支出之上。投资依赖于预期的税后利润，并且非常依赖于企业的乐观程度，因此在经济繁荣时期往往蓬勃发展，而在经济衰退时则会崩溃，使其比 GDP 的其他组成部分或 GDP 本身更具波动性。此外，投资在经济衰退时也可以被推迟，而政府的当前支出和消费则不容易被延迟。例如，家庭在经济衰退时仍然需要花钱购买食品和饮料，而企业可能选择等到经济复苏后再进行投资。我们还将在 1.2.6 节中看到，固定投资决策往往是集中在一起的，这进一步解释了投资的更大波动性。

Growth and cycles 增长与周期

The idea that economies fluctuate between phases of boom and recession is confirmed by looking at the data for the US. Figure 1.2 illustrates the long-run growth and business cycles in the US economy. In the top panel, the log of GDP in constant prices is plotted and shows the rather steady growth rate of GDP over the long run. Using the log scale, a straight line would represent a constant growth rate from 1948 to 2022. 1 1 ^(1){ }^{1} In fact, average annual growth rates in each decade from 1948 were: 4.3 % , 4.5 % , 3.2 % , 3.1 % 4.3 % , 4.5 % , 3.2 % , 3.1 % 4.3%,4.5%,3.2%,3.1%4.3 \%, 4.5 \%, 3.2 \%, 3.1 \%, 3.2 % , 1.9 % , 2.3 % 3.2 % , 1.9 % , 2.3 % 3.2%,1.9%,2.3%3.2 \%, 1.9 \%, 2.3 \%, and 1.5 % 1.5 % 1.5%1.5 \% between 2020 and the first quarter of 2022.
经济在繁荣和衰退阶段之间波动的观点通过观察美国的数据得到了证实。图 1.2 展示了美国经济的长期增长和商业周期。在顶部面板中，以不变价格计算的 GDP 的对数被绘制出来，显示了 GDP 在长期内相对稳定的增长率。使用对数刻度，1948 年至 2022 年期间的直线将代表一个恒定的增长率。实际上，从 1948 年开始，每个十年的平均年增长率分别为： 4.3 % , 4.5 % , 3.2 % , 3.1 % 4.3 % , 4.5 % , 3.2 % , 3.1 % 4.3%,4.5%,3.2%,3.1%4.3 \%, 4.5 \%, 3.2 \%, 3.1 \% 、 3.2 % , 1.9 % , 2.3 % 3.2 % , 1.9 % , 2.3 % 3.2%,1.9%,2.3%3.2 \%, 1.9 \%, 2.3 \% 和 1.5 % 1.5 % 1.5%1.5 \% ，在 2020 年到 2022 年第一季度之间。
Figure 1.2 Business cycles in the United States between 1948 and 2022: Log of real GDP (upper panel) and real GDP growth (lower panel)
图 1.2 1948 年至 2022 年美国的商业周期：实际 GDP 的对数（上图）和实际 GDP 增长（下图）
Note: The shaded grey areas represent recessions as defined by NBER. Both graphs use data from the series ‘Real GDP, chained dollars, billions of chained (2012) dollars.’
注意：阴影灰色区域表示 NBER 定义的经济衰退。两个图表使用的数据来自“实际 GDP，链式美元，十亿链式（2012）美元”系列。
Source: US Bureau of Economic Analysis (data accessed September 2022).
来源：美国经济分析局（数据访问于 2022 年 9 月）。
By plotting the annual growth rate of GDP in the lower panel, the fluctuations of the economy around the long-run trend are highlighted. The dotted line represents the average growth rate between 1948 and 2019 of 3.2 % 3.2 % 3.2%3.2 \%. Peaks and troughs of growth occur about twice a decade. In the US, an independent body called the National Bureau of Economic Research (NBER) establishes the dates of US business cycles and states there have been twelve separate contractions (i.e. recessions) over this period, which are represented by the shaded grey areas on the graphs. Recessions start at the peak of a business cycle and end at the trough: during recessions, economic activity is contracting. In the period we are analysing, the recessions range from 6 to 18 months in duration. This is why the annual GDP growth rate shown in Figure 1.2 is not negative in all of the recessions (e.g. the 2001 recession). The longest of these recessions was the 2007-09 global financial crisis, which spanned a year and a half.
通过在下方图表中绘制 GDP 的年增长率，突显了经济围绕长期趋势的波动。虚线表示 1948 年至 2019 年间的平均增长率 3.2 % 3.2 % 3.2%3.2 \% 。增长的高峰和低谷大约每十年出现两次。在美国，一个名为国家经济研究局（NBER）的独立机构确定美国商业周期的日期，并指出在此期间发生了十二次独立的经济收缩（即衰退），这些衰退在图表上用阴影灰色区域表示。衰退始于商业周期的高峰，结束于低谷：在衰退期间，经济活动正在收缩。在我们分析的期间，衰退的持续时间从 6 个月到 18 个月不等。这就是为什么图 1.2 中显示的年 GDP 增长率在所有衰退中并不都是负值（例如 2001 年的衰退）。其中持续时间最长的衰退是 2007-09 年的全球金融危机，持续了一年半。
Before the global financial crisis many macroeconomists claimed that better policy making had improved macro stability. This led to the use of the term ‘the Great Moderation’ to describe the calmer macroeconomic conditions from the mid-1980s (fewer and shorter recessions as illustrated in Figure 1.2).
在全球金融危机之前，许多宏观经济学家声称更好的政策制定改善了宏观稳定。这导致了“伟大的温和期”这一术语的使用，用以描述从 1980 年代中期开始的更平稳的宏观经济条件（如图 1.2 所示，经济衰退更少且持续时间更短）。
Figure 1.3 Volatility of real GDP growth in the United States: 1950 Q3 to 2019 Q4.
图 1.3 美国实际 GDP 增长的波动性：1950 年第三季度至 2019 年第四季度。
Note: Volatility has been calculated as the standard deviation of the GDP growth rate over a rolling 21-quarter period. Graph uses data from the series ‘Real GDP, chained dollars, billions of chained (2012) dollars.’
注意：波动性是通过对 21 个季度滚动期间的 GDP 增长率计算标准差得出的。图表使用的数据来自“实际 GDP，链式美元，十亿链式（2012）美元”系列。
Source: US Bureau of Economic Analysis (data accessed September 2022).
来源：美国经济分析局（数据访问于 2022 年 9 月）。
A more precise way to document the Great Moderation is to look at the volatility of GDP growth. Figure 1.3 shows the volatility of US GDP growth since the late 1950s. By plotting the moving average of the standard deviation of the growth rate, changes in volatility can be seen easily. Figure 1.3 uses a 21-quarter moving average of the standard deviation of the annual growth rate. There is a noticeable fall in the volatility of GDP growth from the mid 1980s. However, the spike in volatility experienced during the recession brought the era of the Great Moderation to an end. Volatility was low again between the end of the financial crisis and the Covid-19 crisis.
记录“大缓和”的一种更精确的方法是观察 GDP 增长的波动性。图 1.3 显示了自 20 世纪 50 年代末以来美国 GDP 增长的波动性。通过绘制增长率标准差的移动平均，可以很容易地看到波动性的变化。图 1.3 使用了 21 个季度的年度增长率标准差的移动平均。从 20 世纪 80 年代中期开始，GDP 增长的波动性明显下降。然而，在经济衰退期间经历的波动性激增使“大缓和”时代结束。在金融危机结束和新冠疫情之间，波动性再次较低。

1.1.2 Introducing the IS curve
1.1.2 介绍 IS 曲线

In this chapter, we begin to capture essential elements of the complex real-world macro-economy in a model. The model is called the 3-equation model because there are three core elements, representing the demand side, the supply side and the policy maker. The IS is the curve that represents the demand side. It is called the IS curve because it refers to planned investment and savings decisions; hence the I and the S .
在本章中，我们开始在模型中捕捉复杂现实宏观经济的基本要素。该模型被称为三方程模型，因为它有三个核心要素，分别代表需求方、供给方和政策制定者。IS 曲线代表需求方。它被称为 IS 曲线，因为它涉及计划投资和储蓄决策；因此有 I 和 S。
It was originally formulated as a simple shorthand version of John Maynard Keynes’s description of the demand side in his General Theory. 2 2 ^(2){ }^{2}
它最初被制定为约翰·梅纳德·凯恩斯在其《通论》中对需求侧描述的简单速记版本。
By modelling the goods market we can answer interesting questions about the demand side that we might otherwise struggle with, such as the following:
通过对商品市场建模，我们可以回答一些关于需求方面的有趣问题，否则我们可能会很难解决，例如以下问题：
  1. If you give an individual a $ 100 $ 100 $100\$ 100 bonus, how much of it will they spend?
    如果你给一个人一个 $ 100 $ 100 $100\$ 100 奖金，他们会花掉多少？
  2. How much will output increase following a rise in government spending or a boost in the confidence of households and firms about their future prospects?
    政府支出增加或家庭和企业对未来前景信心提升后，产出将增加多少？
  3. To what extent will a rise in the interest rate curtail investment in new housing, machinery and equipment?
    利率上升在多大程度上会抑制对新住房、机械和设备的投资？
The IS curve summarizes how aggregate output in the economy is affected by changes in the spending decisions of families, firms and government bodies. For example, when firms increase their spending on new equipment, this triggers increased production in the capital goods producing sector of the economy. More people are employed to produce the extra capital goods and as they spend their wages, demand for consumer goods goes up and employment and output expand in those sectors as well. As a result of this process, the economy will move to a higher level of output and employment. We shall see that in response to the initial expansion of spending, output will grow until the extra saving households want to make just balances the extra spending on investment. At that point, the process by which the impact of the initial increase in aggregate demand is multiplied through the economy in subsequent rounds of higher employment, spending by newly employed workers, higher demand for consumer goods, etc. comes to an end.
IS 曲线总结了家庭、企业和政府支出决策变化如何影响经济中的总产出。例如，当企业增加对新设备的支出时，这会引发经济中资本品生产部门的生产增加。更多的人被雇用来生产额外的资本品，随着他们花费工资，消费品的需求上升，相关部门的就业和产出也随之扩大。由于这一过程，经济将达到更高的产出和就业水平。我们将看到，作为对初始支出扩张的反应，产出将增长，直到家庭希望额外储蓄的金额恰好平衡对投资的额外支出。在这一点上，初始总需求增加的影响通过随后的更高就业、刚被雇用工人的支出、对消费品的更高需求等在经济中被放大的过程结束。

Aggregate demand in the private sector
私营部门的总需求

Focusing attention on decisions by the private sector, the level of aggregate demand will be affected by current income and by the following factors.
关注私营部门的决策，整体需求水平将受到当前收入和以下因素的影响。
  1. Expectations about the future: The plans of firms to invest in new IT, equipment and premises depend on their expectations of future post-tax profits. If firms experience high levels of capacity utilization and strong order books, they will increase investment in new capacity. Households prefer to have smooth rather than fluctuating consumption, which means they need to save and borrow in order to spread their consumption more evenly over time. To make their saving and borrowing decisions, they must form a view about the future growth of their income. The life-cycle motive for saving refers to the planning of saving as the person takes into account the projected pattern of income during their working life and retirement. Households will revise upward their estimate of how much they can spend each period if they have new information that leads them to expect their income to grow more strongly. Firms and households form their expectations in
    对未来的期望：企业投资新信息技术、设备和场所的计划取决于它们对未来税后利润的预期。如果企业经历高水平的产能利用率和强劲的订单簿，它们将增加对新产能的投资。家庭更倾向于平稳而非波动的消费，这意味着他们需要储蓄和借款，以便在时间上更均匀地分配消费。为了做出储蓄和借款的决策，他们必须对未来收入的增长形成看法。生命周期储蓄动机是指个人在考虑其工作生涯和退休期间的收入预期模式时进行储蓄规划。如果家庭获得新的信息，导致他们预期收入将更强劲增长，他们将上调每个时期的支出估计。企业和家庭在形成预期时会考虑这些因素。
the face of uncertainty. For example, an increase in the unemployment rate in the economy could be a signal to households that uncertainty about their future income has risen, which would trigger an increase in saving for precautionary reasons.
不确定性的面貌。例如，经济中失业率的上升可能向家庭发出信号，表明他们对未来收入的不确定性增加，这将引发出于预防原因的储蓄增加。
2. The extent of credit constraints: These arise because of problems faced by banks in assessing the creditworthiness of households and firms. It is impossible for banks to have full information about borrowers’ projects and actions. Borrowing by households and by small and medium-sized firms is therefore often restricted by banks. Households and business that cannot borrow as much money as they would like are said to be credit constrained. The information problems inherent in bank lending mean that access to credit is often highly dependent on the amount of collateral the borrower has with which to secure the loan. The most common form of collateral for households is the value of their house. This means that changes in the value of collateral, which occur when house prices change, affect consumption and investment because they either tighten or relax credit constraints. People with higher wealth have more collateral and are less likely to be credit-constrained.
2. 信贷约束的程度：这些约束源于银行在评估家庭和企业信用 worthiness 时面临的问题。银行不可能对借款人的项目和行为拥有全面的信息。因此，家庭和中小型企业的借款往往受到银行的限制。无法借到足够资金的家庭和企业被称为信贷受限。银行贷款中固有的信息问题意味着，获得信贷往往高度依赖借款人拥有的抵押品数量。家庭最常见的抵押品形式是他们房屋的价值。这意味着抵押品价值的变化（当房价变化时发生）会影响消费和投资，因为它们要么收紧，要么放松信贷约束。财富较高的人拥有更多的抵押品，因此不太可能受到信贷约束。
3. The interest rate: There are a number of channels through which the interest rate will affect aggregate demand. When interest rates go up, households find it more expensive to get a mortgage. This reduces the demand for new houses and for furnishings and other consumer durables that go along with moving house. A higher interest rate will lead firms to rein in their spending plans on new capital equipment and buildings. Finally, households will tend to postpone consumption spending because of the improved returns from saving, which we call the substitution effect. However, creditor and debtor households would be expected to react differently due to income changes. A creditor household will find their income has gone up when the interest rate rises and this will boost consumption spending through the income effect. For debtor households, the effect will be the opposite. The first and third effects (substitution effects, and income effect for debtors) are normally stronger than the second one (income effect for creditors) and thus a higher interest rate is associated with postponed consumption.
3. 利率：利率通过多种渠道影响总需求。当利率上升时，家庭发现获得抵押贷款的成本更高。这减少了对新房屋以及与搬家相关的家具和其他耐用消费品的需求。更高的利率将导致企业缩减对新资本设备和建筑的支出计划。最后，家庭往往会因为储蓄带来的更高回报而推迟消费支出，这被称为替代效应。然而，债权人家庭和债务人家庭由于收入变化的不同，反应也会有所不同。债权人家庭会发现，当利率上升时，他们的收入增加，这将通过收入效应促进消费支出。对于债务人家庭，效果则相反。第一和第三种效应（替代效应和债务人的收入效应）通常比第二种效应（债权人的收入效应）更强，因此更高的利率与推迟消费相关。

The IS curve IS 曲线

The IS curve summarizes in an equation and diagram the demand side in the macroeconomic model. It shows the combinations of the interest rate and output at which aggregate demand (i.e. spending) in the economy is equal to output.
IS 曲线在宏观经济模型中用一个方程和图表总结了需求侧。它显示了利率和产出之间的组合，在这些组合中，经济中的总需求（即支出）等于产出。
Figure 1.4 shows the IS curve. This is a downward-sloping relationship. To see this, think of the combination of a high interest rate and low output. When the interest rate is high, spending on housing, consumer durables, machinery and equipment will be low. This means aggregate demand is low and a low level of output will satisfy the low demand. Hence, we have the first point on the IS curve at A. Now, take a combination of a low interest rate and high output. Here the situation is the opposite: buoyant spending on new houses, consumer durables and investment goods generates a high level of output and high incomes for households. This second point gives us the downward-sloping IS curve at B.
图 1.4 显示了 IS 曲线。这是一条向下倾斜的关系。要理解这一点，可以考虑高利率和低产出的组合。当利率高时，住房、耐用消费品、机械和设备的支出将会很低。这意味着总需求低，低水平的产出将满足低需求。因此，我们在 A 点得到了 IS 曲线的第一个点。现在，考虑低利率和高产出的组合。在这里，情况正好相反：对新房、耐用消费品和投资品的强劲支出产生了高水平的产出和家庭的高收入。这个第二个点给我们在 B 点得到了向下倾斜的 IS 曲线。
Figure 1.4 The IS curve-the effects of changes in optimism and economic policy. Visit www.oup.com/he/carlin-soskice to explore the IS curve with Animated Analytical Diagram 1.4.
图 1.4 IS 曲线——乐观情绪和经济政策变化的影响。访问 www.oup.com/he/carlin-soskice 探索带有动画分析图 1.4 的 IS 曲线。
To show how changes in profit or income growth expectations, uncertainty and the value of collateral can be captured in the diagram, we hold the interest rate constant and look at shifts in the IS curve. As an example, in a situation of depressed profit expectations, we would expect firms to postpone new investment. The result is lower investment spending at any interest rate. The IS curve shifts to the left (shown by the curve labelled IS (pessimistic expectations)).
为了展示利润或收入增长预期、经济不确定性和抵押品价值如何在图表中体现，我们保持利率不变，观察 IS 曲线的移动。例如，在利润预期低迷的情况下，我们预计企业会推迟新的投资。结果是在任何利率下投资支出减少。IS 曲线向左移动（由标记为 IS（悲观预期）的曲线表示）。
Using the IS diagram, we can show how the central bank or the government can affect the demand side. Following up the situation where the business environment becomes more pessimistic, the central bank could lower the interest rate to stimulate investment. This would be shown as a move along the IS curve from point C C CC to point D D DD. As an example, there was much discussion about the decision by the US central bank, the Federal Reserve, to reduce the policy interest rate and keep it low as a way of stimulating investment in the aftermath of the collapse of the Dotcom bubble in 2001. The long period of low interest rates stimulated investment in new house construction and we shall see in Chapter 9 the role this played in the background to the global financial crisis of 2008.
使用 IS 图，我们可以展示中央银行或政府如何影响需求侧。在商业环境变得更加悲观的情况下，中央银行可以降低利率以刺激投资。这将表现为 IS 曲线从点 C C CC 移动到点 D D DD 。例如，关于美国中央银行——联邦储备委员会——在 2001 年互联网泡沫崩溃后决定降低政策利率并保持低位以刺激投资的讨论很多。长期的低利率刺激了新房建设的投资，我们将在第 9 章看到这在 2008 年全球金融危机背景中所起的作用。
Another response to a leftward shift of the IS curve due to pessimistic profit expectations could be action by the government rather than central bank. If the government decides to launch a major expenditure programme, such as to improve healthcare provision or to install an information super-highway, this will shift the IS curve to the right: at a given interest rate, the government purchases a larger amount of goods and services. Under our assumption that suppliers will respond to the higher demand, the economy moves to a higher level of output and employment. In the diagram, this would shift the IS curve to the right back towards its initial position.
另一个对由于悲观利润预期导致的 IS 曲线向左移动的反应可能是政府而非中央银行采取行动。如果政府决定启动一项重大支出计划，例如改善医疗服务或建设信息高速公路，这将使 IS 曲线向右移动：在给定的利率下，政府购买更多的商品和服务。在我们假设供应商会对更高的需求做出反应的情况下，经济将达到更高的产出和就业水平。在图中，这将使 IS 曲线向右移动，回到其初始位置。
The demand side is only part of the macroeconomic model. To understand how the spending decisions of households, firms and the government fit into the bigger picture,
需求方只是宏观经济模型的一部分。要理解家庭、企业和政府的支出决策如何融入更大的图景，
we need to include the supply side and the motivations and behaviour of the policy makers. Chapter 2 addresses the supply side and Chapter 3 brings in the policy maker. Before moving on, we set out the modelling of the demand side in more detail.
我们需要考虑供应方以及政策制定者的动机和行为。第二章讨论供应方，第三章引入政策制定者。在继续之前，我们更详细地阐述需求方的建模。

1.2 MODELLING 1.2 建模

The Modelling sections of the chapters in the book provide more details of the models and their components introduced in the Overview sections. Detailed derivations of some of the results are available in the appendix.
本书各章的建模部分提供了概述部分中介绍的模型及其组成部分的更多细节。某些结果的详细推导可在附录中找到。
As a first step in this chapter, we introduce the concept of goods market equilibrium and the definition and mechanics of the multiplier process. Throughout this section, we assume that firms are willing to meet the higher demand for their goods and services and workers are willing to take the extra jobs or work the extra hours that are offered.
在本章的第一步中，我们介绍了商品市场均衡的概念以及乘数过程的定义和机制。在本节中，我们假设企业愿意满足对其商品和服务的更高需求，工人也愿意接受额外的工作或加班。

1.2.1 Goods market equilibrium
1.2.1 商品市场均衡

We begin our modelling of the goods market by considering each component of aggregate demand in the closed economy. The aggregate-or economy-wide-demand for goods and services consists of:
我们通过考虑封闭经济中总需求的每个组成部分来开始对商品市场的建模。商品和服务的总需求或经济整体需求包括：
  • consumption: Expenditure by individuals on goods and services. Spending is on both durable products such as a car, laptop or sofa and on non-durable products such as a theatre show, child-care services or groceries.
    消费：个人在商品和服务上的支出。支出包括耐用产品，如汽车、笔记本电脑或沙发，以及非耐用产品，如戏剧表演、儿童保育服务或杂货。
  • investment: Expenditure on goods that produce a stream of utility in the form of future services. When discussing investment as a component of aggregate demand, it includes spending on capital goods (machinery, equipment, and buildings). In addition, most spending on R&D is treated as investment in national accounts. Spending is by households on new houses, by firms on new capital goods, including structures, and building up inventories of materials or finished goods, and by government (on public infrastructure projects, such as building a new high speed rail line).
    投资：对能够产生未来服务流的商品的支出。当讨论投资作为总需求的一个组成部分时，它包括对资本货物（机械、设备和建筑物）的支出。此外，大多数研发支出在国民账户中被视为投资。支出包括家庭对新房的支出，企业对新资本货物（包括建筑物）的支出，以及对材料或成品库存的积累，政府则在公共基础设施项目（如建设新的高速铁路）上进行支出。
  • demand stemming from government purchases: Government expenditure on salaries, goods and services. Spending includes public sector wages (e.g. civil servants, teachers), purchases of goods (e.g. educational supplies, ammunition for the army) and purchases of services (e.g. waste disposal and contract cleaning).
    来自政府采购的需求：政府在薪资、商品和服务上的支出。支出包括公共部门工资（例如，公务员、教师）、商品采购（例如，教育用品、军队弹药）和服务采购（例如，废物处理和合同清洁）。

The model of goods market equilibrium
商品市场均衡模型

We now set out a model of the goods market. In the closed economy, aggregate demand, y D y D y^(D)y^{D}, is given by
我们现在提出一个商品市场模型。在封闭经济中，总需求 y D y D y^(D)y^{D} 由以下公式给出：
y D = C + I + G y D = C + I + G y^(D)=C+I+Gy^{D}=C+I+G
and we ignore imports and exports. All variables are in real terms, which is also referred to as constant price terms. Equilibrium in the goods market requires that planned real expenditure on goods and services (i.e. aggregate demand) is equal to real output
我们忽略进出口。所有变量都是以实际价格计的，也称为恒定价格计。商品市场的均衡要求计划的商品和服务的实际支出（即总需求）等于实际产出。
y D = y , (goods market equilibrium) y D = y ,  (goods market equilibrium)  y^(D)=y,quad" (goods market equilibrium) "y^{D}=y, \quad \text { (goods market equilibrium) }
where y y yy is output. y y yy is also income: spending on the output of the economy in turn becomes the income of those producing it (wages and profits). This circular flow of income to expenditure and output, and back to the incomes of producers means we can use the terms output, income and expenditure interchangeably. We shall come back to the goods market equilibrium condition after providing some more detail about consumption and investment behaviour.
其中 y y yy 是产出。 y y yy 也是收入：对经济产出的支出反过来成为生产者的收入（工资和利润）。这种收入、支出和产出之间的循环流动，以及回到生产者收入的过程，意味着我们可以将产出、收入和支出这几个术语互换使用。在提供一些关于消费和投资行为的更多细节后，我们将回到商品市场均衡条件。
To start, we assume that aggregate consumption is a simple linear function of aftertax or disposable aggregate income
首先，我们假设总消费是税后或可支配总收入的一个简单线性函数
C = c 0 + c 1 ( y − T ) C = c 0 + c 1 ( y − T ) C=c_(0)+c_(1)(y-T)C=c_{0}+c_{1}(y-T)
where T is total taxes.
T 是总税收。
To get the consumption function we make the additional assumption that taxes are a fixed proportion of income; i.e. T = t y T = t y T=tyT=t y, where 0 < t < 1 0 < t < 1 0 < t < 10<t<1. The consumption function then becomes
为了得到消费函数，我们额外假设税收是收入的固定比例；即 T = t y T = t y T=tyT=t y ，其中 0 < t < 1 0 < t < 1 0 < t < 10<t<1 。消费函数因此变为
C = c 0 + c 1 ( 1 − t ) y . (Keynesian consumption function) C = c 0 + c 1 ( 1 − t ) y .  (Keynesian consumption function)  C=c_(0)+c_(1)(1-t)y.quad" (Keynesian consumption function) "\mathrm{C}=\mathrm{c}_{0}+\mathrm{c}_{1}(1-t) y . \quad \text { (Keynesian consumption function) }
This is a Keynesian consumption function. It consists of a constant term, c 0 c 0 c_(0)\mathrm{c}_{0}, which is referred to as autonomous consumption because it does not depend on current income, and the other component of consumption, c 1 ( 1 − t ) y c 1 ( 1 − t ) y c_(1)(1-t)yc_{1}(1-t) y, which fluctuates with the level of disposable income. Since we assume a proportional tax rate, t , c 1 ( 1 − t ) y t , c 1 ( 1 − t ) y t,c_(1)(1-t)yt, c_{1}(1-t) y is a fixed proportion of disposable income. c 1 c 1 c_(1)c_{1} is referred to as the marginal propensity to consume and lies between zero and one ( 0 < c 1 < 1 0 < c 1 < 1 0 < c_(1) < 10<c_{1}<1 ).
这是一个凯恩斯消费函数。它由一个常数项 c 0 c 0 c_(0)\mathrm{c}_{0} 组成，这被称为自主消费，因为它不依赖于当前收入，另一个消费组成部分 c 1 ( 1 − t ) y c 1 ( 1 − t ) y c_(1)(1-t)yc_{1}(1-t) y 则随着可支配收入的水平波动。由于我们假设一个比例税率， t , c 1 ( 1 − t ) y t , c 1 ( 1 − t ) y t,c_(1)(1-t)yt, c_{1}(1-t) y 是可支配收入的固定比例。 c 1 c 1 c_(1)c_{1} 被称为边际消费倾向，介于零和一之间（ 0 < c 1 < 1 0 < c 1 < 1 0 < c_(1) < 10<c_{1}<1 ）。
Note that the marginal propensity to consume (MPC) shows the change (where change is denoted by a triangle symbol) in consumption as the result of a change in post-tax or disposable income:
注意，边际消费倾向（MPC）显示消费的变化（变化用三角符号表示）是由于税后或可支配收入的变化所导致的：
MPC ≡ Δ C Δ y disp = c 1 , (marginal propensity to consume) MPC ≡ Δ C Δ y disp  = c 1 ,  (marginal propensity to consume)  MPC-=(DeltaC)/(Deltay^("disp "))=c_(1),quadquad" (marginal propensity to consume) "\mathrm{MPC} \equiv \frac{\Delta \mathrm{C}}{\Delta y^{\text {disp }}}=c_{1}, \quad \quad \text { (marginal propensity to consume) }
where y disp ≡ ( 1 − t ) y y disp  ≡ ( 1 − t ) y y^("disp ")-=(1-t)yy^{\text {disp }} \equiv(1-t) y. 在哪里 y disp ≡ ( 1 − t ) y y disp  ≡ ( 1 − t ) y y^("disp ")-=(1-t)yy^{\text {disp }} \equiv(1-t) y 。
In this model of consumption, private saving is S ≡ y disp − C S ≡ y disp  − C S-=y^("disp ")-C\mathrm{S} \equiv y^{\text {disp }}-\mathrm{C} and adds to one’s assets. Income is the amount that can be consumed without reducing one’s assets. The corresponding marginal propensity to save is s 1 s 1 s_(1)s_{1} and c 1 + s 1 = 1 c 1 + s 1 = 1 c_(1)+s_(1)=1c_{1}+s_{1}=1 (i.e. disposable income can be either saved or spent).
在这种消费模型中，私人储蓄为 S ≡ y disp − C S ≡ y disp  − C S-=y^("disp ")-C\mathrm{S} \equiv y^{\text {disp }}-\mathrm{C} ，并增加个人资产。收入是可以消费而不减少个人资产的金额。相应的边际储蓄倾向为 s 1 s 1 s_(1)s_{1} 和 c 1 + s 1 = 1 c 1 + s 1 = 1 c_(1)+s_(1)=1c_{1}+s_{1}=1 （即可支配收入可以被储蓄或消费）。
If disposable income is zero, the Keynesian consumption function predicts consumption equal to c 0 c 0 c_(0)c_{0}. For this to be the case, households have savings and/or are able to borrow. A more satisfactory model of consumption must therefore include forwardlooking behaviour in order to account for savings and we build this in to the model of consumption later in the chapter.
如果可支配收入为零，凯恩斯消费函数预测消费等于 c 0 c 0 c_(0)c_{0} 。要使这种情况成立，家庭必须有储蓄和/或能够借款。因此，更令人满意的消费模型必须包括前瞻性行为，以便考虑储蓄，我们将在本章后面将其纳入消费模型中。

1.2.2 The multiplier 1.2.2 乘数

We use the Keynesian consumption function to introduce in the simplest way the concept of how equilibrium in the goods market is determined and how the multiplier process works. If we substitute the consumption function into the equation for aggregate demand, then we get a relation between aggregate demand,
我们使用凯恩斯消费函数以最简单的方式引入商品市场均衡如何确定以及乘数过程如何运作的概念。如果我们将消费函数代入总需求的方程中，那么我们就得到了总需求之间的关系。
y D = c 0 + c 1 ( 1 − t ) y + I + G y D = c 0 + c 1 ( 1 − t ) y + I + G y^(D)=c_(0)+c_(1)(1-t)y+I+Gy^{D}=c_{0}+c_{1}(1-t) y+I+G
Figure 1.5 Keynesian cross-increase in government spending. Visit www.oup.com/he/carlin-soskice to explore the Keynesian cross with Animated Analytical Diagram 1.5.
图 1.5 凯恩斯交叉——政府支出增加。访问 www.oup.com/he/carlin-soskice 探索带有动画分析图 1.5 的凯恩斯交叉。
and output, y y yy, which we can draw on a diagram with output on the x x xx-axis and aggregate demand on the y y yy-axis (Figure 1.5). The intercept of the curve will be ( I + G + c 0 I + G + c 0 I+G+c_(0)I+G+c_{0} ) and the slope c 1 ( 1 − t ) c 1 ( 1 − t ) c_(1)(1-t)c_{1}(1-t) which, given the assumption that both c 1 c 1 c_(1)c_{1} and t t tt are between 0 and 1 , will itself be between zero and one. We can also draw the goods market equilibrium condition on the same graph, which will be a 45 ∘ 45 ∘ 45^(@)45^{\circ} line, because in equilibrium
并输出 y y yy ，我们可以在图表上绘制输出在 x x xx 轴上，聚合需求在 y y yy 轴上（图 1.5）。曲线的截距将是（ I + G + c 0 I + G + c 0 I+G+c_(0)I+G+c_{0} ），斜率 c 1 ( 1 − t ) c 1 ( 1 − t ) c_(1)(1-t)c_{1}(1-t) ，根据假设 c 1 c 1 c_(1)c_{1} 和 t t tt 都在 0 和 1 之间，斜率本身也将在零和一之间。我们还可以在同一图表上绘制商品市场均衡条件，这将是一条 45 ∘ 45 ∘ 45^(@)45^{\circ} 线，因为在均衡状态下。
y = y D y = y D y=y^(D)y=y^{D}
The point at which the two curves intersect shows the level of output where planned real expenditure on goods (and services) by firms, households and government is exactly equal to the level of goods being supplied in the economy. Above the 45 ∘ 45 ∘ 45^(@)45^{\circ} line, the demand for goods is greater than the supply.
两条曲线交点所示的点表示企业、家庭和政府对商品（和服务）的计划实际支出与经济中供应的商品水平完全相等的产出水平。在 45 ∘ 45 ∘ 45^(@)45^{\circ} 线以上，商品的需求大于供应。
To understand the model, we disturb the initial equilibrium at point A. Suppose there is an increase in government spending. From the aggregate demand equation, we can see that this shifts the aggregate demand curve upwards by the change in government spending, Δ G Δ G DeltaG\Delta \mathrm{G}. Aggregate demand now exceeds output (Point B). As the government increases its purchases of goods (e.g. of office equipment) the stocks of these goods in warehouses decline. The inventory management software records the fall in stocks and triggers an increase in production: output rises. This is the move from B to C, where once again y = y D y = y D y=y^(D)y=y^{D}. The higher output in turn raises incomes (in the form of wages of the additional workers employed and the profits of the owners of the firms making higher sales) and according to the consumption function, some proportion of
为了理解模型，我们在 A 点扰动初始均衡。假设政府支出增加。从总需求方程可以看出，这将使总需求曲线因政府支出的变化而向上移动， Δ G Δ G DeltaG\Delta \mathrm{G} 。此时，总需求超过了产出（B 点）。随着政府增加对商品（例如办公设备）的采购，这些商品在仓库中的库存减少。库存管理软件记录库存的下降，并触发生产的增加：产出上升。这是从 B 到 C 的转变，再次 y = y D y = y D y=y^(D)y=y^{D} 。更高的产出反过来提高了收入（以额外雇佣工人的工资和销售额增加的公司的利润的形式），根据消费函数，某个比例的
the higher income is spent on goods and services in the economy, raising aggregate demand further. The process continues until the new goods market equilibrium is reached at point Z Z ZZ, where output and aggregate demand are equal.
更高的收入用于购买经济中的商品和服务，进一步提高了总需求。这个过程持续进行，直到新的商品市场均衡在点 Z Z ZZ 达到，此时产出和总需求相等。
Adjustment to shifts in aggregate demand via inventory accumulation and decumulation shows how a purely quantity based adjustment to a new goods market equilibrium can take place. For the goods market to be in equilibrium it must be the case that y = y D y = y D y=y^(D)y=y^{D}. If we substitute y y yy into the aggregate demand equation we can rearrange to define equilibrium output in terms of the exogenous variables. Exogenous variables are those that are determined outside the model. In the model of goods market equilibrium, the exogenous variables are autonomous consumption ( c 0 c 0 c_(0)c_{0} ), investment (I) and government spending ( G ) ( G ) (G)(G), the marginal propensity to consume ( c 1 ) c 1 (c_(1))\left(c_{1}\right) and the tax rate ( t ) ( t ) (t)(t). If we know the value of these five variables, we can work out the level of equilibrium output,
通过库存积累和去积累对总需求变化的调整显示了如何通过纯粹的数量调整实现新的商品市场均衡。为了使商品市场处于均衡状态，必须满足 y = y D y = y D y=y^(D)y=y^{D} 。如果我们将 y y yy 代入总需求方程，我们可以重新排列以定义外生变量的均衡产出。外生变量是指在模型外部确定的变量。在商品市场均衡模型中，外生变量包括自主消费（ c 0 c 0 c_(0)c_{0} ）、投资（I）和政府支出 ( G ) ( G ) (G)(G) 、边际消费倾向 ( c 1 ) c 1 (c_(1))\left(c_{1}\right) 和税率 ( t ) ( t ) (t)(t) 。如果我们知道这五个变量的值，就可以计算出均衡产出的水平。
y = c 0 + c 1 ( 1 − t ) y + I + G y − c 1 ( 1 − t ) y = c 0 + I + G y = 1 1 − c 1 ( 1 − t ) ⏟ multiplier ( c 0 + I + G ) ⏟ autonomous demand y = c 0 + c 1 ( 1 − t ) y + I + G y − c 1 ( 1 − t ) y = c 0 + I + G y = 1 1 − c 1 ( 1 − t ) ⏟ multiplier  c 0 + I + G ⏟ autonomous demand  {:[y=c_(0)+c_(1)(1-t)y+I+G],[y-c_(1)(1-t)y=c_(0)+I+G],[y=ubrace((1)/(1-c_(1)(1-t))ubrace)_("multiplier ")ubrace((c_(0)+I+G)ubrace)_("autonomous demand ")]:}\begin{aligned} y & =c_{0}+c_{1}(1-t) y+\mathrm{I}+\mathrm{G} \\ y-c_{1}(1-t) y & =c_{0}+\mathrm{I}+\mathrm{G} \\ y & =\underbrace{\frac{1}{1-c_{1}(1-t)}}_{\text {multiplier }} \underbrace{\left(c_{0}+\mathrm{I}+\mathrm{G}\right)}_{\text {autonomous demand }} \end{aligned}
Because c 1 c 1 c_(1)c_{1} and t t tt are between 0 and 1 , this simplified model implies that the multiplier is greater than 1 . This means that a 1 % 1 % 1%1 \% increase in autonomous demand would be predicted to lead to an increase in output of more than 1 % 1 % 1%1 \%. This is referred to as the short-run multiplier as we hold the interest rate and all other policy responses constant-i.e. output is the only variable allowed to change. Note that if consumption was not a function of current income, i.e. if the marginal propensity to consume, c 1 c 1 c_(1)c_{1}, is equal to zero, then the aggregate demand line is horizontal and there is no multiplier process amplifying the impact on the economy of the rise in government spending. A rule of thumb is that the multiplier in ‘normal times’ is between one and 1.5; higher values are estimated for recessions.
因为 c 1 c 1 c_(1)c_{1} 和 t t tt 在 0 和 1 之间，这个简化模型意味着乘数大于 1。这意味着自主需求的 1 % 1 % 1%1 \% 增加预计会导致产出增加超过 1 % 1 % 1%1 \% 。这被称为短期乘数，因为我们保持利率和所有其他政策反应不变，即产出是唯一允许变化的变量。请注意，如果消费不是当前收入的函数，即边际消费倾向 c 1 c 1 c_(1)c_{1} 等于零，那么总需求线是水平的，没有乘数过程放大政府支出增加对经济的影响。一个经验法则是，在“正常时期”乘数在 1 到 1.5 之间；在衰退期间，估计更高的值。
In the consumption function, c 0 c 0 c_(0)c_{0}