18 CHAPTER AS-AD 與景氣循環

學習本章後，您將能 C H A P T E R C H E C K L I S T 提供經濟衰退的技術定義，並描述景氣循環 1 定義總合供給，並描述影響總合供給的因素 2 Economists are ambivalent about the aggregate supply-aggregate demand (AS-AD) model. Real business cycle theorists, who like to build their models from the base of production functions and preferences, don’t use the model because the AS and AD curves are not independent. Technological change shifts both the AS and AD curves simultaneously and in complicated ways. New Keynesian economists have dropped the model in favor of a dynamic variant that places the inflation rate on the y‐axis and the output gap (real GDP minus potential GDP as a percentage of potential GDP) on the x‐axis. Despite attacks on the model from both sides of the doctrinal spectrum, those of us who spend a good part of our professional lives teaching the principles course recognize the AS-AD model as the key macroeconomic model. For us, the model plays a similar role in the organization of the macroeconomics to that played by the demand and supply model in microeconomics. That is the view taken in this textbook. The AS-AD model is the best model currently available for introducing students to macroeconomics. It enables them to gain insights into the way the economy works, to organize their study of the subject, and to understand the debates surrounding the effects of policies designed to improve macroeconomic performance. 定義總合需求，並描述影響總合需求的因素 3 解釋總合需求與總合供給的波動如何造成景氣循環 4

18.2 總合供給 實質 GDP 取決於 勞動受僱數量 資本數量、人力資本與技術狀態 土地與自然資源的數量 企業才能

18.2 總合供給 在充分就業下： 勞動市場均衡決定勞動受僱數量，此為充分就業的勞動數量 實質 GDP 為 GDP 潛能 在景氣循環的過程中： 勞動受僱數量在充分就業水準上下波動 實質 GDP 在 GDP 潛能上下波動

總合供給的基本 18.2 總合供給 總合供給 是指實質 GDP 供給量與物價水準的關係 其他影響生產的因素保持不變，

18.2 總合供給 沿著 GDP 潛能的垂直線，當物價水準變動，名目工資與其他生產要素的名目價格也隨之變動，且變動的程度等於物價水準變動的程度，以保持實質工資或實質價格處於充分就業的均衡水準

18.2 總合供給 圖 18.1 總合供給曲線 總合供給曲線 AS 代表實質 GDP 供給量與物價水準的關係，而其他影響生產的因素保持不變 It’s difficult to start using the AS-AD model until you are convinced that students have bought into the notion that the aggregate supply curve is upward sloping and the reasons behind it. The AS curve that is used in this chapter is a short-run aggregate supply curve because it assumes that product prices and resources prices do not move in lock step with one another. That is to say that wages, materials prices, energy prices and the like move with a lag behind product prices. To launch your lecture, walk through this thought experiment with your students. Ask your class if firms are likely to be motivated to step up production in the face of rising product prices. They will have no trouble responding in the affirmative. Now tell your students that the higher price is actually the result of an increase in the general price level. Ask them how quickly workers are likely to respond by asking for wage increases. The answer is that it will take time for workers to see that the general price level has risen and that their real wages are now lower. Eventually they will demand higher wages. Firms will grant the wage increase in the face of higher profits. But until workers realize that their real wage has fallen, firms are in the position of receiving higher prices with no change in money wages so they increase their production. And with this result, you have demonstrated the upward-sloping aggregate supply curve!

18.2 總合供給 1. GDP 潛能等於 $10 兆，物價水準等於110，實質 GDP 等於 GDP 潛能

總合供給的變動 18.2 總合供給 物價水準以外之其他影響生產的因素變動，導致總合供給的變動 這些因素包括： GDP 潛能 名目工資 其他生產要素的名目價格

18.2 總合供給 GDP 潛能的變動 任何造成 GDP 潛能變動的因素也會造成總合供給曲線的移動 圖 18.2 GDP 潛能增加

18.2 總合供給 1. GDP 潛能增加，則總合供給增加 2. 總合供給曲線由 AS0 右移至 AS1

18.2 總合供給 名目工資與其他生產要素名目價格的變動 名目工資與其他生產要素名目價格變動，導致廠商的成本變動，於是總合供給變動 名目工資與其他生產要素名目價格越高，則廠商的成本越高，廠商的供給量越少，於是總合供給減少

18.2 總合供給 圖 18.3 名目工資的變動 名目工資上漲，導致總合供給減少。總合供給曲線由 AS0 左移至 AS2 名目工資變動不會導致 GDP 潛能變動

18.3 總合需求 實質 GDP 需求量 (Y) 等於消費支出 (C)、投資 (I)、政府支出 (G) 與出口 (X) 的總和減去進口 (M) 亦即， Y = C + I + G + X – M

總合需求的基本 18.3 總合需求 總合需求 是指實質 GDP 需求量與物價水準的關係，而其他影響支出的因素保持不變。 當其他條件不變下，

.3 總合需求 圖 18.4 總合需求曲線 總合需求曲線 AD 代表實質 GDP 需求量與物價水準的關係，而其他影響支出的因素保持不變

18.3 總合需求 1. 物價上漲導致實質 GDP 需求量減少 2. 物價下跌導致實質 GDP 需求量增加

總合需求的變動 18.3 總合需求 物價水準以外之其他影響支出的因素變動，則導致總合需求的變動 總合需求增加，則總合需求曲線右移 總合需求減少，則總合需求曲線左移 Some of the same issues regarding change in demand and change in quantity demanded not only apply in the microeconomic model but also apply to the aggregate supply and aggregate demand curves as well. Remind your students that a change in the price level does not shift the aggregate supply curve or aggregate demand curve. A change in the price level results in movements along the curves. You can also involve your students in the material by asking them a few hypothetical questions. Ask your class what will happen to the aggregate demand curve in each of the following cases: a. A cut in taxes. b. An increase in expected future profit. c. A cut in government spending. d. An increase in foreign income. e. A rise in the price level abroad. Each of these examples gives students practice shifting the aggregate demand curve rightward and leftward as well as understanding why it shifts in the direction that it does.

18.3 總合需求 影響總合需求變動的因素包括： 未來的預期 財政政策與貨幣政策 全球經濟的狀況

18.3 總合需求 預期 預期未來所得增加將導致現今的消費增加，則總合需求增加 預期未來的通貨膨脹上升，將導致人們在目前價格較低時增加消費，於是總合需求增加 預期未來的利潤增加，將導致廠商現今的投資增加，於是總合需求增加

18.3 總合需求 財政政策與貨幣政策 政府可藉由租稅、移轉支付與政府支出來影響總合需求 減稅、增加移轉支付或政府支出增加，將導致總合需求增加。 降低利率或增加貨幣數量將導致總合需求增加。

18.3 總合需求 全球經濟 全球經濟影響總合需求的兩項主要因素為：匯率與外國所得。 其他條件不變下，本國貨幣升值則總合需求減少。本國貨品與服務的相對價格較高，於是出口減少；購買力升高或外國貨品與服務相對價格較低，於是進口增加。 外國所得增加則對本國貨品與服務的需求增加，於是出口增加，總合需求增加

18.3 總合需求 圖 18.5 總合需求的變動 1. 總合需求增加，如果 預期未來所得、通貨膨脹與利潤增加 政府或中央銀行採取導致支出增加的政策 貨幣貶值或全球經濟擴張

29.3 總合需求 2. 總合需求減少，如果 預期未來所得、通貨膨脹與利潤減少 政府或中央銀行採取導致支出減少的政策 貨幣升值或全球經濟衰退

18.4 瞭解景氣循環 總合供給與總合需求決定實質 GDP 與物價水準 總體經濟均衡 發生於實質 GDP 需求量等於實質 GDP 供給量之際，亦即總合需求曲線 AD 與總合供給曲線 AS 的交點 圖 18.6(a) 總體經濟均衡

18.4 瞭解景氣循環 如果物價水準等於 120 ，實質 GDP 等於 $11 兆，如 E 點所示 實質 GDP 需求量小於實質 GDP 供給量，廠商無法售出全部的產量，於是庫存增加，廠商降低產量與價格

18.4 瞭解景氣循環 如果物價水準等於 100 ，實質 GDP 等於 $9 兆，如 A 點所示 實質 GDP 需求量大於實質 GDP 供給量，廠商無法滿足對其產品的需求，於是庫存減少，廠商增加產量與調高價格

18.4 瞭解景氣循環 總體經濟均衡為物價水準等於 110，實質 GDP 等於$10 兆

18.4 瞭解景氣循環 總體經濟均衡下的三種可能： 1. 低於充分就業水準的均衡，實質 GDP 低於 GDP 潛能

總合需求的波動 18.4 瞭解景氣循環 總合需求的波動是景氣循環的原因之一 為了專注於總合需求的波動，假設 GDP 潛能與充分就業的物價水準保持不變 圖 18.7 總合需求循環 Don’t neglect the predictions of the model. This is the payoff for the student. With this simple model, we can now say quite a lot about growth, inflation, and the business cycle. However, when you do so, be aware that the AS-AD model predicts a fall in the price level when either aggregate demand decreases or aggregate supply increases. And the model predicts that real GDP decreases when either aggregate supply or aggregate demand decreases. But, some students object by pointing out that GDP rarely decreases and the price level rarely falls. These students are bothered by this apparent mismatch between the predictions of the model and the observed economy. The best way to handle this issue is to emphasize that in our actual economy, aggregate supply and aggregate demand almost always are increasing. When we use the model to simulate the effects of a decrease in either aggregate supply and aggregate demand, we’re studying what happens relative to the trends in real GDP and the price level. A fall in the price level in the model translates into a lower price level than would otherwise have occurred and a slowing of inflation. The story is similar for real GDP.

18.4 瞭解景氣循環 總合需求波動造成實質 GDP 在 GDP 潛能上下波動

18.4 瞭解景氣循環 經濟在第 2 年達到景氣循環的波峰，實質 GDP 高於 GDP 潛能，經濟處於高於充分就業的均衡 第 3 年經濟回復至充分就業

18.4 瞭解景氣循環 經濟在第 4 年達到景氣循環的波谷，實質 GDP 低於 GDP 潛能，經濟處於低於充分就業的均衡 經濟在第 5 年回復至充分就業

總合供給的波動 18.4 瞭解景氣循環 停滯性通貨膨脹 總合供給波動的原因分成兩種型態： GDP 潛能成長的速度 主要資源的價格變動

18.4 瞭解景氣循環 圖 18.8 石油價格循環 石油價格上漲導致總合供給減少，總合供給曲線 由AS 左移至 AS1. 實質 GDP 減少，物價水準上漲 停滯性通貨膨脹

18.4 瞭解景氣循環 石油價格下跌，總合供給增加，總合供給曲線由 AS 右移至 AS2. 實質 GDP 增加，物價水準下跌 景氣擴張

朝向充分就業的調整 18.4 瞭解景氣循環 膨脹缺口 衰退缺口 實質 GDP 大於 GDP 潛能，造成物價上漲 Reinforce the movement toward long-run equilibrium with a curve-shifting exercise. Take the case where the AD curve shifts rightward. The fact that the initial equilibrium occurs where the new AD curve intersects the AS curve is not difficult. But the notion that the AS curve shifts leftward as time passes is difficult for many students. The trick to making this idea clear is to spend enough time when initially discussing the AS curve so that the students realize that wages and other input prices remain constant along an AS curve. Once the students see this point, they can understand that, as input prices increase in response to the higher level of prices, the AS curve shifts leftward. Avoid confusing students by using ‘up’ to correspond to a decrease in aggregate supply. But do point out that that when the AS curve shifts leftward it is moving vertically upward, as input prices rise to become consistent with potential GDP and the new long-run equilibrium price level. Most students find it easier to see why the AS curve shifts leftward once they see that rising input prices shift the curve vertically upward

18.4 瞭解景氣循環 圖 18.9 朝向充分就業的調整 實質 GDP 大於 GDP潛能 — 形成膨脹缺口 — 造成物價上漲

29.4 瞭解景氣循環 GDP 潛能大於實質 GDP —形成衰退缺口 — 造成物價下跌