AD-AS Model Key Points | AD-AS 模型考点精讲

📚 AD-AS Model Key Points | AD-AS 模型考点精讲

The AD-AS model is the cornerstone of A-Level macroeconomics. It explains how the overall price level and real national output (GDP) are determined by the interaction of aggregate demand and aggregate supply. Mastering this model is essential for analysing economic fluctuations, inflation, unemployment, and the effects of government policy.

AD-AS 模型是 A-Level 宏观经济学的基石。它解释了总体价格水平和实际国民产出（GDP）是如何由总需求与总供给的相互作用决定的。掌握这一模型对于分析经济波动、通货膨胀、失业以及政府政策的效果至关重要。

1. Introduction to AD-AS Model | AD-AS 模型简介

The Aggregate Demand–Aggregate Supply model brings together all the key macroeconomic variables on a single diagram. The vertical axis shows the general price level (P), and the horizontal axis shows real GDP or real national output (Y). The model allows us to analyse short-run fluctuations and long-run growth.

总需求–总供给模型将所有的关键宏观经济变量汇集在一张图中。纵轴表示一般价格水平（P），横轴表示实际 GDP 或实际国民产出（Y）。该模型使我们能够分析短期波动和长期增长。

The intersection of AD and AS determines the equilibrium price level and equilibrium real output. Any change in the components of AD or AS will shift the curves and lead to new macroeconomic outcomes.

AD 曲线与 AS 曲线的交点决定了均衡价格水平和均衡实际产出。AD 或 AS 任何一个组成部分的变化都会导致曲线移动，并产生新的宏观经济结果。

2. Aggregate Demand (AD) | 总需求

Aggregate demand is the total planned spending on domestic goods and services at a given price level over a period of time. The formula is: AD = C + I + G + (X – M), where C is consumption, I is investment, G is government spending, X is exports and M is imports.

总需求是在一定时期内，在给定价格水平下，对国内商品和服务的计划支出总和。公式为：AD = C + I + G + (X – M)，其中 C 是消费，I 是投资，G 是政府支出，X 是出口，M 是进口。

AD = C + I + G + (X – M)

Each component has distinct determinants. Consumption depends on income, wealth, interest rates and consumer confidence. Investment is influenced by interest rates, business confidence, technology and retained profits.

每个组成部分都有不同的决定因素。消费取决于收入、财富、利率和消费者信心。投资受利率、商业信心、技术和留存利润的影响。

3. The AD Curve: Why It Slopes Down | AD 曲线为何向下倾斜

The AD curve shows an inverse relationship between the general price level and real GDP. When the price level falls, the quantity of real output demanded increases. Three key effects explain this downward slope.

AD 曲线反映了总体价格水平与实际 GDP 之间的反向关系。当价格水平下降时，实际产出需求量增加。三个关键效应解释了这种向下倾斜的斜率。

Real wealth effect: A lower price level raises the real value of households’ money balances and financial assets, encouraging more consumption (C).

实际财富效应：更低的价格水平提高了家庭货币余额和金融资产的实际价值，从而鼓励更多的消费（C）。

Interest rate effect: A lower price level reduces the demand for money for transactions, which puts downward pressure on interest rates. Lower interest rates stimulate investment (I) and durable goods consumption.

利率效应：更低的价格水平减少了交易性的货币需求，给利率带来下行压力。更低的利率刺激投资（I）和耐用品消费。

Net export effect: A lower domestic price level makes domestic goods relatively cheaper than foreign goods, increasing exports (X) and decreasing imports (M), thus boosting net exports (X – M).

净出口效应：更低的国内价格水平使国内商品相对于外国商品更便宜，增加出口（X）并减少进口（M），从而提升净出口（X – M）。

4. Shifts in the AD Curve | AD 曲线的移动

A change in any component of AD (C, I, G, X, M) that is not caused by a change in the price level will shift the entire AD curve. A rise in C, I, G or X, or a fall in M, shifts AD to the right. A fall in C, I, G or X, or a rise in M, shifts AD to the left.

任何不是由价格水平变化引起的 AD 组成部分（C、I、G、X、M）变化都会导致整条 AD 曲线移动。C、I、G 或 X 的增加，或 M 的减少，使 AD 向右移动。C、I、G 或 X 的减少，或 M 的增加，使 AD 向左移动。

AD 扩张 (AD Shifts Right)	AD 收缩 (AD Shifts Left)
减税 (Tax cuts) → 可支配收入上升	增税 (Tax rises) → 可支配收入下降
利率下调 (Lower interest rates) → 刺激借贷	利率上调 (Higher interest rates) → 抑制借贷
政府支出增加 (Higher government spending)	政府削减支出 (Cuts in government spending)
本币贬值 (Depreciation of currency) → 净出口上升	本币升值 (Appreciation of currency) → 净出口下降
消费者/企业信心增强 (Rising confidence)	消费者/企业信心减弱 (Falling confidence)

Note that a change in the price level causes a movement along the AD curve, not a shift. Shifts are caused by autonomous changes in spending.

请注意，价格水平的变化导致沿着 AD 曲线的移动，而不是曲线的平移。曲线平移是由自主性支出变化引起的。

5. Short-Run Aggregate Supply (SRAS) | 短期总供给

Short-run aggregate supply shows the total quantity of goods and services that firms are willing and able to produce at each price level, holding input prices and capital stocks partly fixed. The SRAS curve slopes upwards because, in the short run, at least one factor of production is fixed while output prices are flexible.

短期总供给表示在每个价格水平下，企业愿意并且能够生产的商品和服务的总量，其中投入价格和资本存量部分固定。SRAS 曲线向上倾斜，因为在短期内，至少有一种生产要素是固定的，而产出价格是灵活的。

There are several explanations for the upward-sloping SRAS: sticky-wage theory, sticky-price theory (menu costs) and misperceptions theory. When the price level rises, nominal wages or input costs may not adjust immediately, so firms find it more profitable to raise output.

对于 SRAS 向上倾斜有几种解释：黏性工资理论、黏性价格理论（菜单成本）以及错觉理论。当价格水平上升时，名义工资或投入成本可能不会立即调整，因此企业发现增加产出更有利润可图。

In the short run, actual output can deviate from the long-run potential output (Yf) due to price level changes or supply shocks.

在短期内，实际产出可能因价格水平变化或供给冲击而偏离长期潜在产出（Yf）。

6. Shifts in SRAS | SRAS 曲线的移动

The SRAS curve shifts when there are changes in the costs of production across the economy. A decrease in costs shifts SRAS to the right; an increase in costs shifts SRAS to the left.

当经济中生产成本发生变化时，SRAS 曲线会发生移动。成本下降使 SRAS 向右移动；成本上升使 SRAS 向左移动。

Key factors shifting SRAS:

Changes in nominal wages: A rise in wages shifts SRAS leftward.
Changes in raw material and energy prices: E.g., a rise in oil prices is a negative supply shock.
Changes in indirect taxes or subsidies: An increase in VAT shifts SRAS left; a new subsidy shifts SRAS right.
Exchange rate changes: A depreciation raises the cost of imported inputs, shifting SRAS left.
Supply shocks: Natural disasters, conflicts or pandemics can reduce supply and shift SRAS left.

移动 SRAS 的关键因素：

名义工资的变化：工资上升使 SRAS 向左移动。
原材料和能源价格的变化：例如，石油价格上涨是一种负面的供给冲击。
间接税或补贴的变化：增值税增加使 SRAS 左移；新补贴使 SRAS 右移。
汇率变化：本币贬值提高了进口投入品的成本，使 SRAS 左移。
供给冲击：自然灾害、冲突或流行病会减少供给，使 SRAS 左移。

7. Long-Run Aggregate Supply (LRAS) | 长期总供给

The long-run aggregate supply curve is vertical at the full-employment level of real output (Yf), also known as potential output. In the long run, all prices and wages are fully flexible, so the economy gravitates to its natural level of output, independent of the price level.

长期总供给曲线在充分就业的实际产出水平（Yf）处垂直，该水平也称为潜在产出。在长期，所有价格和工资都完全弹性，因此经济趋向于其自然产出水平，独立于价格水平。

The position of LRAS depends on the quantity and quality of factors of production (land, labour, capital) and the state of technology. It represents the economy’s maximum sustainable output.

LRAS 的位置取决于生产要素（土地、劳动、资本）的数量和质量以及技术水平。它代表了经济所能维持的最大产出。

Some economists (Keynesians) argue that LRAS can be horizontal at very low levels of output, but the standard A-Level model assumes a vertical LRAS at Yf.

一些经济学家（凯恩斯主义）认为，在产出水平极低时，LRAS 可以是水平的，但标准的 A-Level 模型假定在 Yf 处有一条垂直的 LRAS。

8. Shifts in LRAS | LRAS 曲线的移动

LRAS shifts rightwards when the economy’s productive capacity expands. This represents long-run economic growth and arises from improvements on the supply side of the economy.

当经济的生产能力扩张时，LRAS 向右移动。这代表了长期的经济增长，源于经济供给侧的改善。

Factors that shift LRAS to the right include:

Increases in the labour force (through birth rate, immigration or higher participation rates).
Increases in the capital stock (investment in machinery, infrastructure).
Improvements in technology and productivity.
Discovery of new natural resources.
Institutional improvements, such as better education and training, or deregulation that increases efficiency.

使 LRAS 向右移动的因素包括：

劳动力增加（通过出生率、移民或更高的劳动参与率）。
资本存量增加（对机器、基础设施的投资）。
技术和生产力的提高。
发现新的自然资源。
制度改善，如更好的教育和培训，或提高效率的放松管制。

A leftward shift of LRAS is rare but can occur due to war, natural disasters causing permanent damage to capital and infrastructure, or a significant decline in the labour force.

LRAS 左移很少见，但可能因战争、自然灾害对资本和基础设施造成永久性破坏，或者劳动力显著下降而发生。

9. Macroeconomic Equilibrium | 宏观经济均衡

Macroeconomic equilibrium occurs where the AD curve and the AS curve intersect. There are two key equilibrium concepts: short-run equilibrium and long-run equilibrium.

宏观经济均衡发生在 AD 曲线与 AS 曲线的交点处。有两个关键的均衡概念：短期均衡和长期均衡。

Short-run equilibrium: AD = SRAS. This determines the actual price level and actual real output (Y1). The economy may be in an inflationary gap (Y1 > Yf) or a deflationary gap (Y1 < Yf).

短期均衡：AD = SRAS。这决定了实际价格水平和实际产出（Y1）。经济可能处于通胀缺口（Y1 > Yf）或通缩缺口（Y1 < Yf）状态。

Long-run equilibrium: AD = SRAS = LRAS. At this point, the economy is at full employment (Y = Yf) and there is no tendency for the price level to change automatically. All adjustments have worked through.

长期均衡：AD = SRAS = LRAS。在这一点，经济处于充分就业状态（Y = Yf），并且价格水平没有自动变化的趋势。所有调整已完成。

Understanding these gaps is crucial for analysing business cycles and the need for stabilisation policy.

理解这些缺口对于分析经济周期以及稳定政策的必要性至关重要。

10. Effects of Shifts in AD | AD 移动的影响

An increase in AD (rightward shift) will, in the short run, raise both the price level and real output. The extent of the changes depends on the slope of the SRAS curve. If the economy is near full capacity (steep SRAS), the price level rises significantly while output changes little. If there is plenty of spare capacity (flat SRAS), output rises significantly with little inflation.

AD 增加（向右移动）在短期内将同时提高价格水平和实际产出。变化的程度取决于 SRAS 曲线的斜率。如果经济接近充分产能（SRAS 陡峭），价格水平显著上升而产出变化很小。如果存在大量闲置产能（SRAS 平坦），产出显著增加，通胀很小。

Over time, if the economy is producing above Yf (positive output gap), wages and input prices will tend to rise, shifting SRAS to the left until the economy returns to Yf but at a higher price level. This is the self-correcting mechanism.

随着时间的推移，如果经济生产超过 Yf（正产出缺口），工资和投入价格将趋于上涨，促使 SRAS 向左移动，直到经济回到 Yf，但价格水平更高。这就是自我纠正机制。

A decrease in AD (leftward shift) reduces both price level and real output in the short run. This can create a deflationary gap with rising unemployment. In the long run, falling wages and input costs may shift SRAS to the right, restoring Yf at a lower price level. However, wages are often sticky downwards, making this process slow.

AD 减少（向左移动）在短期内会降低价格水平和实际产出。这可能造成通缩缺口，失业率上升。长期来看，工资和投入成本下降可能使 SRAS 右移，在更低的价格水平恢复 Yf。然而，工资往往具有向下黏性，使得这一过程缓慢。

11. Effects of Shifts in AS | AS 移动的影响

A rightward shift in SRAS (or LRAS) is highly desirable: it increases real output and reduces the price level simultaneously. Such a shift is often termed a positive supply shock and is the goal of supply-side policies.

SRAS（或 LRAS）向右移动是非常理想的：它同时增加实际产出并降低价格水平。这种移动通常称为正向供给冲击，也是供给侧政策的目标。

A leftward shift in SRAS, known as a negative supply shock, causes ‘stagflation’: a combination of rising prices (inflation) and falling real output, leading to higher unemployment. The classic example is a sharp increase in oil prices.

SRAS 向左移动，即负向供给冲击，会导致“滞胀”：价格上涨（通胀）与实际产出下降并存，导致失业率上升。经典的例子是石油价格急剧上升。

In the face of a negative supply shock, policymakers face a dilemma: expansionary demand policies can mitigate the fall in output but worsen inflation; contractionary demand policies can curb inflation but deepen the recession. There is no easy solution from demand management alone.

面对负向供给冲击，政策制定者面临两难：扩张性需求政策可以缓解产出下降，但会加剧通胀；紧缩性需求政策可以抑制通胀，但会加深衰退。仅靠需求管理并无容易的解决之道。

12. Using AD-AS for Policy Analysis | 运用 AD-AS 进行政策分析

The AD-AS model provides a powerful framework for evaluating fiscal and monetary policies. Expansionary fiscal policy (higher G, lower taxes) shifts AD to the right, suitable for closing a deflationary gap. Contractionary fiscal policy (lower G, higher taxes) shifts AD to the left, used to cool an overheating economy.

AD-AS 模型为评估财政政策和货币政策提供了有力的框架。扩张性财政政策（增加 G，减税）使 AD 右移，适合弥合通缩缺口。紧缩性财政政策（减少 G，增税）使 AD 左移，用于给过热的经济降温。

Monetary policy works through interest rates and the money supply. A cut in the policy rate lowers borrowing costs, encouraging C and I, shifting AD to the right. A rise in the rate does the opposite.

货币政策通过利率和货币供给起作用。降低政策利率降低了借贷成本，鼓励 C 和 I，使 AD 右移。提高利率则相反。

Supply-side policies aim to shift LRAS and/or SRAS to the right. Examples include investment in education and training, infrastructure spending, tax reforms to incentivise work and investment, and deregulation. These policies can raise potential output without generating inflationary pressure.

供给侧政策旨在使 LRAS 和/或 SRAS 向右移动。例子包括对教育和培训的投资、基础设施建设、激励工作和投资的税制改革以及放松管制。这些政策可以在不产生通胀压力的情况下提高潜在产出。

Students must be able to draw and interpret the AD-AS diagram, illustrating the effects of various shocks and policies. The ability to explain the transition from short-run to long-run equilibrium using automatic adjustment mechanisms is a key higher-order skill.

学生必须能够绘制和解读 AD-AS 图，说明各种冲击和政策的影响。能够解释利用自动调整机制从短期均衡向长期均衡过渡，是一项关键的高阶技能。

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AD-AS Model Key Points | AD-AS 模型考点精讲