第15章AD—AS模型

1、 第第1515章章 ADAS模型模型 總需求：總需求： 0 Y1 Y2 GDP P P1 P2 AD 0 r y r1 y1 r2 y2 IS LM（p1） LM（p2） E2 E1 0 P y P1 y1 P2 y2 AD D2 D1 0 r y r1 y0 r0 y IS LM（p0） E E P P0 AD IS 0 y y0y EE AD ， y0 N* N0 y* y * = F（N*，K*） 0 )( P W NN dd 0N0N1N W/P W P （ ） 0 W P （ ） 1 Nd= Nd （ ） W P )( P W NN ss 0N0N1N W/P W P （ ） 0 W

2、 P （ ） 1 NS= NS （ ） W P 0N0N1N W/P W P （ ） 0 W P （ ） 2 NS= NS （ ） W P E Nd= Nd （ ） W P N2 是指總產(chǎn)量與一般價格水平之間是指總產(chǎn)量與一般價格水平之間 的關(guān)系。在以價格水平為縱坐標(biāo)，總產(chǎn)量為橫坐的關(guān)系。在以價格水平為縱坐標(biāo)，總產(chǎn)量為橫坐 標(biāo)的坐標(biāo)系中，標(biāo)的坐標(biāo)系中，即為即為 按照按照 ，宏觀經(jīng)濟(jì)學(xué)將總產(chǎn)出與，宏觀經(jīng)濟(jì)學(xué)將總產(chǎn)出與 價格水平之間的關(guān)系分為價格水平之間的關(guān)系分為即即 0yyf P 0 y yf P E0 E1 AD0 AD1 AD0 AD1 P0 P1 0yyf P E0 E1 D P0 P1 y

3、0 0yyf P E0 E1 P0 AD 1 y0 AD 1 AD 0 AD 0 0yyf P E C A B B A C 0y yf P AS P0E0 AS AD AD 0yyf P AS P0E0 AD0 AS AD0 AD1 AD1 y1 P1 E1 0yyf P AD P0 E0 AS0 AS1 y1 P1E1 AS0 AS1 AD 對總需求總供給模型的論述可以說是本書對總需求總供給模型的論述可以說是本書 到目前為止對全部宏觀經(jīng)濟(jì)理論作出的到目前為止對全部宏觀經(jīng)濟(jì)理論作出的 總結(jié)?？偨Y(jié)。 這一論述涉及了這一論述涉及了 和和 。它們中的每一個都可以。它們中的每一個都可以 用數(shù)學(xué)方程式表

4、示。用數(shù)學(xué)方程式表示。 M P = L1（y）+ L2（r） f（N）= M P ； h（N）= M P y = y（N，K） 類型類型 NI 決定模型 (簡單的凱恩斯模型) IS-LM模型 (調(diào)整的凱恩斯模型) AD-AS模型 (完整的凱恩斯模型) 市場市場 狀況狀況 產(chǎn)品市場產(chǎn)品市場產(chǎn)品市場和貨幣市場產(chǎn)品市場和貨幣市場 產(chǎn)品市場、貨幣市場產(chǎn)品市場、貨幣市場 和勞動力市場和勞動力市場 假設(shè)假設(shè) 利率、價格不變，利率、價格不變， 不考慮貨幣因素不考慮貨幣因素 價格不變，價格不變， 考慮貨幣因素考慮貨幣因素 利率、價格均變，利率、價格均變， 考慮考慮 AS因素因素 研究研究 內(nèi)容內(nèi)容 從總支出角

5、度分析從總支出角度分析 從國民收入和利率角從國民收入和利率角 度分析度分析 從國民收入和價格角從國民收入和價格角 度分析度分析 坐標(biāo)坐標(biāo) 軸軸 橫軸：國民收入橫軸：國民收入(Y) 縱軸縱軸:總支出（總支出（AE） 橫軸：國民收入橫軸：國民收入(Y) 縱軸縱軸:利率（利率（r） 橫軸：國民收入橫軸：國民收入(Y) 縱軸縱軸:價格（價格（P） Aggregate Supply The quantity of real GDP supplied is the total quantity that firms plan to produce during a given period. It dep

6、ends on The quantity of the labor employed The quantity of physical and human capital State of technology We distinguish two time frames associated with different states of the labor market: Long-run aggregate supply Short-run aggregate supply Long-Run Aggregate Supply Long-run aggregate supply is t

7、he relationship between the quantity of real GDP supplied and the price level when real GDP equals potential GDP. Potential GDP is independent of the price level. So the long-run aggregate supply curve (LAS) is vertical at potential GDP. n Figure shows the LAS curve with potential GDP of $12 trillio

8、n. uAlong the LAS curve, all prices and wage rates vary by the same percentage so relative prices and the real wage rate remain constant. Short-Run Aggregate Supply Short-run aggregate supply is the relationship between the quantity of real GDP supplied and the price level when the money wage rate,

9、the prices of other resources, and potential GDP remain constant. A rise in the price level with no change in the money wage rate and other factor prices increases the quantity of real GDP supplied. The short-run aggregate supply curve (SAS) is upward sloping. Figure shows a short-run aggregate supp

10、ly curve (SAS). uAlong the SAS curve, real GDP supplied might be above potential GDP uor below potential GDP. The SAS curve is upward sloping because: A rise in the price level with no change in costs induces firms to bear a higher marginal cost and increase production; and A fall in the price level

11、 with no change in costs induces firms to decrease production to lower marginal cost. Three models of aggregate supply The sticky-wage model The imperfect-information model The sticky-price model All three models imply: () e YYPP natural rate of output a positive parameter the expected price level t

12、he actual price level agg. output The sticky-wage model Assumes that firms and workers negotiate contracts and fix the nominal wage before they know what the price level will turn out to be. The nominal wage they set is the product of a target real wage and the expected price level:e WP e WP PP Targ

13、e t real wage The sticky-wage model If it turns out that e WP PP e PP e PP e PP then Unemployment and output are at their natural rates. Real wage is less than its target, so firms hire more workers and output rises above its natural rate. Real wage exceeds its target, so firms hire fewer workers an

14、d output falls below its natural rate. The sticky-wage model Implies that the real wage should be counter-cyclical, should move in the opposite direction as output during business cycles: In booms, when P typically rises, real wage should fall. In recessions, when P typically falls, real wage should

15、 rise. This prediction does not come true in the real world: The cyclical behavior of the real wage Percentage change in real wage Percentage change in real GDP -5 -4 -3 -2 -1 0 1 2 3 4 5 -3-2-1012345678 1974 1979 1991 1972 2004 2001 1998 1965 1984 1980 1982 1990 The imperfect-information model Assu

16、mptions: All wages and prices are perfectly flexible, all markets are clear. Each supplier produces one good, consumes many goods. Each supplier knows the nominal price of the good she produces, but does not know the overall price level. The imperfect-information model Supply of each good depends on

17、 its relative price: the nominal price of the good divided by the overall price level. Supplier does not know price level at the time she makes her production decision, so uses the expected price level, P e. Suppose P rises but P e does not. Supplier thinks her relative price has risen, so she produ

18、ces more. With many producers thinking this way, Y will rise whenever P rises above P e. The sticky-price model Reasons for sticky prices: long-term contracts between firms and customers menu costs firms not wishing to annoy customers with frequent price changes Assumption: Firms set their own price

19、s (e.g., as in monopolistic competition). The sticky-price model An individual firms desired price is where a 0. Suppose two types of firms: firms with flexible prices, set prices as above firms with sticky prices, must set their price before they know how P and Y will turn out: ()pPYYa () eee pPYYa

20、 The sticky-price model Assume sticky price firms expect that output will equal its natural rate. Then, () eee pPYYa e pP nTo derive the aggregate supply curve, we first find an expression for the overall price level. nLet s denote the fraction of firms with sticky prices. Then, we can write the ove

21、rall price level as The sticky-price model Subtract (1s )P from both sides: (1)() e Ps PsPYYa price set by flexible price firms price set by sticky price firms (1) () e sPs PsYYa nDivide both sides by s : (1) () e s PPYY s a The sticky-price model High P e High P If firms expect high prices, then fi

22、rms that must set prices in advance will set them high. Other firms respond by setting high prices. High Y High P When income is high, the demand for goods is high. Firms with flexible prices set high prices. The greater the fraction of flexible price firms, the smaller is s and the bigger is the ef

23、fect of Y on P. (1) () e s PPYY s a The sticky-price model Finally, derive AS equation by solving for Y : (), e YYPP where () s s 1 a (1) () e s PPYY s a The sticky-price model In contrast to the sticky-wage model, the sticky-price model implies a pro-cyclical real wage: Suppose aggregate output/inc

24、ome falls. Then, Firms see a fall in demand for their products. Firms with sticky prices reduce production, and hence reduce their demand for labor. The leftward shift in labor demand causes the real wage to fall. Summary & implications Each of the three models of agg. supply imply the relationship

25、summarized by the SRAS curve & equation. Y PLRAS Y SRAS () e YYPP e PP e PP e PP Suppose a positive AD shock moves output above its natural rate and P above the level people had expected. Y PLRAS SRAS1 SRAS equation: e YYPP() 11 e PP AD1 AD2 2 e P 2 P 33 e PP Over time, P e rises, SRAS shifts up, an

26、d output returns to its natural rate. 1 YY 2 Y 3 Y SRAS2 Movements Along the LAS and SAS Curves Figure shows that a change in the price level with an equal percentage change in the money wage causes a movement along the LAS curve. no change in the money wage causes a movement along the SAS curve. Ch

27、anges in Aggregate Supply When potential GDP increases, both the LAS and SAS curves shift rightward. Potential GDP changes, for three reasons: The full-employment quantity of labor changes The quantity of capital (physical or human) changes Technology advances Figure shows how an increase in potential GDP shifts the LAS curve and the SAS curve shifts along with the LAS curve. Figure shows the effect of a change in the money wage rate on aggregate supply. A rise in the money wage rate Decreases short- run ag