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30 總合支出 CHAPTER

C H A P T E R C H E C K L I S T 學習本章後，您將能：

If you want to talk about Keynes and his contribution to economics, this is probably the best place to do it. A Keynes biographical sketch can be found at The aggregate expenditure model, presented in this chapter, is the essence of Keynes General Theory. Don Patinkin, a leading historian of economic thought and Keynes scholar, said that the innovation of the General Theory was to replace price with income (GDP) as the equilibrating variable. This version of the model cannot be found in the General Theory, mainly because Keynes was writing before the national income accounting system had been developed. So he made up his own aggregates, based on employment and a money wage measure of the price level. But the words and equations of the General Theory can be translated readily into the textbook version of the model. This version of the model first appeared in The Elements of Economics, a textbook authored by Lorie Tarshis published in It was popularized by Paul Samuelson in the first edition of his celebrated text published in 1948.

30.1 支出計畫與實質 GDP 所得與支出循環流量模型顯示總合支出等於： 消費支出 C 投資 I 政府支出 G 淨出口 NX

30.1 支出計畫與實質 GDP 如果總合計畫支出等於實質 GDP，則廠商的庫存等於支出計畫的庫存

30.1 支出計畫與實質 GDP 實際支出等於計畫支出加上廠商非計畫的庫存變動，又等於實質 GDP 與總所得

30.1 支出計畫與實質 GDP 圖 30.1 消費函數 A 點代表自發性消費等於 \$1.5 兆

30.1 支出計畫與實質 GDP 45° 線上任何一點都代表消費支出等於可支配所得 1. 當消費函數在 45° 線上，儲蓄為負值

3.當消費函數與 45° 線相交時，儲蓄等於 0 30.1 支出計畫與實質 GDP 2.當消費函數在 45° 線之下，則儲蓄為正值

30.1 支出計畫與實質 GDP 邊際消費傾向 邊際消費傾向 (MPC) 是指可支配所得的變動量引起消費支出的變動量 MPC = 消費支出的變動量 可支配所得的變動量

30.1 支出計畫與實質 GDP 圖 30.2 邊際消費傾向 1. 可支配所得 \$2 兆的變動量引起

30.1 支出計畫與實質 GDP 影響消費的其他因素 這些因素也同樣影響消費支出，例如： 可支配所得 實質利率 淨資產的購買力

30.1 支出計畫與實質 GDP 可支配所得的變動引起沿著消費函數線的移動，其他因 素則造成整條消費函數的移動 例如，

30.1 支出計畫與實質 GDP 圖 30.3 消費函數的移動 1. 消費支出增加，消費函數上移，當 實質利率下跌 淨資產購買力上升

30.1 支出計畫與實質 GDP 2. 消費支出增加，消費函數上移，當 實質利率上漲 淨資產購買力下降 預期未來所得減少 消費支出(\$兆)

30.1 支出計畫與實質 GDP 邊際進口傾向 為進口與實質 GDP 的關係 進口與 GDP 進口是誘發性支出的另一項組成要素。

30.2 支出計畫與實質 GDP 圖 30.4 總合支出規劃 總合支出為： 投資 (I)、 政府支出 (G)、 出口 (X) 及

30.2 支出計畫與實質 GDP 圖 30.5 均衡支出 總合計畫支出(\$兆) 實質GDP大於計畫支出 1. 當總合計畫支出大於實質 GDP，庫存非計畫地減少，廠商增加生產，實質 GDP 增加 計畫支出大於實質GDP 實質GDP(\$兆) (a)均衡支出 2. 當總合計畫支出小於實質 GDP，庫存非計畫地增加，廠商減少生產，實質 GDP 降低 庫存非計畫地減少 庫存非計畫地增加 實質GDP(\$兆) (b)非計畫的庫存變動

30.2 支出計畫與實質 GDP 3. 當總合計畫支出等於實質 GDP，非計畫庫存的變動等於 0，實質 GDP 等於均衡水準

30.3 支出乘數 當投資增加，則總合支出與實質 GDP 皆增加 ，但實質 GDP 的增加量大於投資的增加量 乘數 是指自發性支出變動 ( 例如投資 ) 所引起實質 GDP 變動量，為自發性支出變動量的倍數 There are several ways to approach the derivation of the multiplier. The most accessible way to launch your lecture is allow students to “get their hands dirty” by performing a couple of quick calculations. Ask your students to assume that your classroom is a small city and that you are interested in building a brand new factory there. Assume that the initial expenditure will be \$100 million. Pretend to write out a check to the first general contractor (a student in the first row). This contractor will pay the workers, the next student. (You can explain to the class that you are assuming everything is constructed using only labor for simplicity. Nothing changes except adding complications if you take account of intermediate inputs.) Ask the class to assume that everyone’s marginal propensity to consume is 0.9. So the first worker will spend \$90 million in total. You can either ask the stuChapter dent what he or she would buy or you can suggest an item, such as cars. In any case, the student spends the income by handing it to the very next student, who, coincidentally manufactures cars or whatever the student buys. So the \$90 million in expenditure is income to the next student who, in turn, will spend \$81 million. You can continue these rounds as spending through as many iterations as you want. But, regardless of the number, have the class keep a running tally of all the spending and income that is created from the initial expenditure. [Continued on next slide]

Now ask if this process will ever come to an end. A bright math student might argue that the process never really comes to an end because what you have here is an infinite geometric series. Make sure to compliment the student’s insight but explain that the process does come to an end because the series converges. That is, at some point the income that will be generated for the next person will become arbitrarily close to zero. Explain to your students that what they have just witnessed is the multiplier. Once they see this demonstration, the multiplier becomes quite intuitive!

30.3 支出乘數 圖 30.6 乘數 1. 投資增加 \$0.5 兆，總合支出曲線由 AE0 上移 \$0.5 兆，至 AE1

30.3 支出乘數 乘數的大小 乘數等於均衡支出的變動量除以自發性支出的變動量 亦即， 乘數 = 均衡支出的變動量 自發性支出的變動量

Y = C + I C = MPC  Y Y = MPC  Y + I 30.3 支出乘數

30.3 支出乘數 解 Y ，得 (1 – MPC)  Y = I 於是 Y = I (1 – MPC)

30.3 支出乘數 I Y = (1 – MPC) 等號兩邊同除以 I ，得 1 Y = I (1 – MPC)
(1 – 0.75) 1 Y I = 0.25 = 4.

30.3 支出乘數 所得稅也使得乘數變小的原因如下：

30.3 支出乘數 邊際稅率決定應繳所得稅變動 邊際稅率 為實質 GDP 中用於繳納所得稅的比重 邊際稅率越高，則自發性支出變動引起的可支配所得與實質 GDP 的變動越小，乘數越小

30.3 支出乘數 邊際進口傾向、邊際稅率與邊際消費傾向共同決定 AE 曲線的斜率，進而影響了乘數的大小 乘數的一般公式為： 1 Y =
I = 1

30.3 支出乘數 圖 30.7 乘數與 AE 曲線的斜率 沒有進口與課稅的情況，AE 曲線的斜率等於 MPC = 0.75

30.3 支出乘數 進口與課稅導致 AE 曲線斜率變成 0.5 於是乘數等於 2 (b)乘數等於2 總合計畫支出(\$兆)

30.4 AD 曲線與均衡支出 均衡支出取決於物價水準 其他條件不變而物價水準上漲，總合計畫支出減少， AE 下移，均衡支出減少

30.4 AD 曲線與均衡支出 圖 30.8 均衡支出與總合需求 當物價水準為 110 時，AE 曲線為 AE0.

30.4 AD 曲線與均衡支出 當物價水準為 90 時，AE 曲線上移至 AE1. 均衡支出增加至 C 點的 \$11 兆

30.4 AD 曲線與均衡支出 當物價水準為 130 時，AE 曲線下移至 AE2. 均衡支出減少至 A 點的 \$9 兆