4 CHAPTER 需求與供給

C H A P T E R C H E C K L I S T 學習本章後，您將能： 區別需求量與需求的差異，瞭解需求的決定因素 1 區別供給量與供給的差異，瞭解供給的決定因素 2 解釋需求與供給如何決定市場價格與數量，以及需求與供 給變動的影響 3

競爭市場 本章所探討的是有眾多買方與賣方，且單一買方或賣方無法影響價格的競爭市場

4.1 需求 需求量 在特定價格與期間下，人們願意且能夠購買的貨品、服務或資源數量 需求量是每單位時間下對應的數量 例如：每天、每月 Don’t dive right in by drawing a demand-supply graph on the board. Tease the ideas out of the students with one of these exercises: Quick exercise to generate demand curve: Pick a good (say a slice of pizza) and propose that a person would be willing to buy one slice at a price of $4. Now pick a student and ask the student if you reduced the price to $3 a slice, how much pizza would he or she be willing to buy. Next ask the same student how much he or she would buy at $2 per slice and then ask about $1 a slice. It is helpful for you to pick the initial price and quantity so the student has a starting point for the subsequent choices. You are then guaranteed an easy-to-graph relationship between price and quantity. Do this same experiment for one or two more students. Use the data provided by your volunteer students by collecting the demand schedule on the board. Graph the resulting demand curve, explicitly labeling the axes. Make the point that as the price of a slice falls the students are willing to buy more slices, and that as the price of a slice rises the students are willing to buy fewer slices. Then inform the students that they have just “discovered” the law of demand! Finally, use the demand curve by moving between several points on the curve. Emphasize that these “movements along the demand curve” are a change in the quantity demanded and are the result of changes in the price of a slice of pizza.

需求法則 4.1 需求 在其他條件不變下， 價格上漲，則需求量減少 價格下跌，則需求量增加 Experiment to generate demand curve (needs about 30 minutes): Of the hundreds of classroom experiments that are available today, very few are worth the time they take to conduct. The classic demand-revealing experiment is one of the most productive and worthwhile ones. Bring to class 2 bottles of ice-cold, ready-to-drink, Coke or bottled water or sports drink. (If your class is very large, bring 6 bottles). Tell the students that you have these drinks and ask them to indicate if they would like one. Most hands will go up and you are now ready to make two points: (i) The students have just revealed a want but not a demand. (ii) You don’t have enough bottles to satisfy their wants, so you need an allocation mechanism. Ask the students to suggest some allocation mechanisms. You might get suggestions such as: give them to the oldest, the youngest, the tallest, the shortest, the first-to-the-front-of-the-class. For each one, point out the difficulty/inefficiency/inequity. If no one suggests selling them to the highest bidder, tell the class that you are indeed going to do just that. Tell them that this auction is real. The winner will get the drink and will pay. Ask for a show of hands of those who have some cash and can afford to buy a drink. Explain that these indicate an ability to buy but not a definite plan to buy. Begin the auction. Appoint a student to count hands (more than one for a big class) and appoint another student to keep a spreadsheet (see the Parkin Website for a sample that you can download). [continued on next slide note]

需求規劃與需求曲線 4.1 需求 需求 在影響購買的其他因素不變下，價格與需求量的關係。 需求是所有不同價格與數量之間的整體關係，以需求規劃或需求曲線表示 Begin at a low price: say 10¢ a bottle and count the number willing to buy. Raise the price in 10¢ increments and keep tally of the number who are willing to buy at each price. When the number willing to buy equals the number of bottles you have for sale, do the transactions. (If you make a profit, and you might do so, tell the students that the profit, small though it is, will go the department fund for undergraduate activities—and deliver on that promise.) Now use the data to make a demand curve for Coke (or other drink) in your classroom today. Emphasize the law of demand. Also emphasize that every demand curve relates to a market for the good (as defined by geography or some other spatial dimension) and for a given time period. Now that you have a demand curve, you can do some thought experiments that will shift it. Ask: How would this demand curve have been different if the temperature in the classroom was 10 degrees higher/lower? How would this demand curve have been different if half the class was sick and absent today? How would this demand curve have been different if there was a Coke machine right in the classroom? (Save your demand data for later. We’ll make some suggestions for its further use in Chapter 5 on the elasticity of demand.)

4.1 需求 需求規劃 需求曲線 在影響購買的其他因素不變下，不同價格所對應之需求量明細表 在影響購買的其他因素不變下，貨品需求量與其價格之間的關係

4.1 需求

4.1 需求 個人需求與市場需求 市場需求 市場上全部買方的需求總和 市場需求曲線是個人需求曲線的水平加總

4.1 需求

4.1 需求 需求的變動 當影響購買的其他因素變動，則產生需求的變動 需求的變動代表產生一個新的需求規劃及需求曲線

4.1 需求 圖 4.3 需求的變動 1. 當需求減少，則需求曲線 D0 向左移至 D1.

4.1 需求 影響需求變動的主要因素為： 相關貨品的價格 所得 預期 購買者數目 偏好

4.1 需求 替代品 相關貨品價格 可以取代某貨品用途的他項貨品 例如：蘋果和橘子 如果替代品的價格上漲，則需求增加 若替代品價格下跌，則需求減少

4.1 需求 互補品 必須與某貨品共同使用的他項物品 例如：護膝與直排輪 若互補品的價格上漲，則需求減少 若互補品的價格下跌，則需求增加

4.1 需求 所得 正常財 因所得增加而導致需求增加，或因所得減少而導致需 求減少的貨品 劣等財 因所得增加而導致需求減少，或所得減少而導致需求增加的貨品

4.1 需求 預期 預期未來所得與價格會影響貨品的需求 例如：若預料下個月電腦價格將會下跌，則近期電腦的需求將會減少 購買者的數目 市場的購買者越多，則貨品需求越大

4.1 需求 偏好 當偏好改變，對某一項貨品的需求增加，並使得另一項貨品的需求減少 偏好因為下列因素改變： 人們的瞭解程度 新產品的出現

4.1 需求 需求量的變動與需求的變動 需求量的變動 貨品本身的價格變動導致 需求的變動 貨品本身價格之外，任何影響購買的其他因素變動導致

4.1 需求 圖 4.4 需求量的變動與需求的變動 When you draw a shift of the demand, be careful to draw the arrows in the horizontal direction. Follow the text by always describing shifts of demand and supply curves as “rightward” or “leftward.” Do not say that the curves shift “up” or “down” or “inward” or “outward.”

供給量 在特定價格與期間之下，廠商願意且能夠銷售貨品、服務、或資源的數量 供給法則 在其他條件不變下， 4.2 供給 價格上漲，則供給量增加 價格下跌，則供給量減少

供給規劃與供給曲線 4.2 供給 供給 影響銷售的其他因素不變下，價格與供給量間的關係 供給是所有不同價格與供給量之間的整體關係 Estimating the supply of Coke (or bottled water) in the classroom. It is best to do this next classroom activity on a different day from the demand experiment.) Tell the students that you would like a Coke (or other drink) that is available from a machine somewhere near the classroom and you want someone to get it for you. You are going to continue teaching while the student is out of the room and you will be giving hints about what is on the next test. Ask the students to raise their hand if they are willing to fetch one can of Coke if you pay, say $5.00. Write down the number. Lower the price you’re willing to pay in $1 increments until the number of students willing to fetch you the drink begins to decrease. Keep track of the numbers. Then lower the price you’re willing to pay in 25¢ increments until you get close to only having one student willing to fetch you the drink. Keep track of the numbers. Lower the price in smaller increments if necessary until just one student is willing to fetch you a drink. Now use the data to make a supply curve for Coke (or other drink) in your classroom today. Emphasize the law of supply. Emphasize that every supply curve relates to a market for the good (as defined by geography or some other spatial dimension) and for a given time period. Now that you have a supply curve, you can do some thought experiments that will shift it. Ask: How would this supply curve have been different if the coke machine was a mile away? How would this supply curve have been different if half the class was sick and absent today? How would this supply curve have been different if there was a Coke machine right in the classroom? How would this supply curve have been different if the temperature in the classroom was 10 degrees higher/lower?

4.2 供給 供給規劃 影響銷售的其他因素不變下，不同價格對應供給量的明細表 供給曲線 影響銷售的其他因素不變下，供給量與價格間的關係

4.2 供給

4.2 供給 個人供給與市場供給 市場供給 市場上全部賣方的供給總和 市場的供給曲線是個人供給曲線的水平加總

4.2 供給

4.2 供給 供給的變動 貨品本身價格外，任何影響銷售的其他因素變動，則產生供給的變動 供給的變動代表產生新的供給規劃與供給曲線

4.2 供給 4.2 SUPPLY 圖 4.7 供給的變動 1. 供給減少，供給曲線 S0 向左移至 S1. When you draw a shift of the supply curve, again be careful to draw the arrows in the horizontal direction. Follow the text by always describing shifts of supply curves as “rightward” or “leftward.” Do not say that the curves shift “up” or “down.” This description of a shift is especially confusing for the supply curve. A rightward shift of the supply curve makes it look as if the curve is moving lower. Students who do not think in terms of “rightward” and “leftward” believe this shift reflects a decrease in supply, which is wrong. Get the student to always go left and right and draw the shift arrows too.

4.2 供給 影響供給變動的主要因素為： 相關貨品的價格 生產要素價格 預期 銷售者的數目 生產力

4.2 供給 生產過程中的替代品 相關貨品的價格 某項貨品的價格變動可能會導致另一項貨品供給的變動 某貨品的生產會取代另一項貨品的生產。例如：紙廠生產的紙板與印表紙。 替代品價格下跌，則貨品的供給增加 替代品價格上漲，則貨品的供給減少

4.2 供給 生產過程中的互補品 生產某貨品而附帶生產出的另一項貨品。例如，奶油與脫脂牛奶 互補品價格上漲，則貨品的供給增加 互補品價格下跌，則貨品的供給減少

4.2 供給 生產要素價格 生產要素價格影響成本。 在其他條件不變下，生產成本上升則供給減少。 預期 預期未來價格影響貨品供給的情況 預期未來生產要素價格影響貨品供給的情況

4.2 供給 生產者數目 市場上生產者數目越多則供給越大 生產力 每單位生產要素的產量 生產力上升代表成本降低，於是供給增加。例如：技術的進步。 生產力下滑代表成本上升，則供給減少。例如：颶風

供給量的變動與供給的變動 4.2 供給 供給量的變動 供給的變動 貨品本身價格變動導致供給量的變動 貨品本身價格以外，任何影響銷售的其他因素變動導致

4.2 供給 圖 4.8 供給量的變動與供給的變動

市場均衡 均衡價格 均衡數量 需求量等於供給量 — 當購買者與銷售者的計劃是一致的 4.3 市場均衡 當需求量等於供給量時的價格 對應均衡價格的數量

4.3 市場均衡 圖 4.9 均衡價格與均衡數量 1. 市場均衡發生在需求曲線與供給曲線的交點 2. 均衡價格等於 $1 / 瓶 3. 均衡數量等於 1,000 萬瓶 / 天

價格：市場的自動調整機制 4.3 市場均衡 市場調整法則 短缺 或 超額需求 過剩 或 超額供給 當市場產生短缺時，則價格上漲 當市場產生過剩時，則價格下跌 短缺 或 超額需求 需求量大於供給量的情況 過剩 或 超額供給 供給量大於需求量的情況 The law of market forces is important, so you want your students to grasp why prices are driven to the equilibrium. You can choose a good, like concert tickets to the hottest band. Draw a demand-supply graph with a reasonable equilibrium price and quantity. Ask the students what would happen if the concert promoter decided to charge only $10 a ticket. Would students line up before dawn to buy them? Yes! Explain that this is a case of excess demand. Ask them what could the promoter do to get the crowds to go away? Hopefully they will answer, “Raise ticket prices!” Show them how the market pressures the price to rise to the equilibrium price and use the graph to show how the promoter and students move up their respective supply and demand curves. You can do the same thing for excess supply. Let the promoter try to sell tickets for $1,000 each. Again, move down along the supply and demand curves as the market pressures the price to fall.

4.3 市場均衡 圖 4.10(a) 達成市場均衡的力量 在價格為 $0.75 / 瓶時， 1. 需求量等於 1,100 萬瓶 2. 供給量等於 900 萬瓶 3. 短缺 200 萬瓶 The magic of market equilibrium and the forces that bring it about and keep the market there need to be demonstrated with the basic diagram, with intuition, and, if you’ve got the time, with hard evidence in the form of further class activity. If you did the demand experiment, you might want to begin with that and explain that in the classroom market, the supply was fixed (so there was vertical supply curve) at the quantity of bottles that you brought to class. The equilibrium occurred where the market demand curve (demand by the students) intersected your supply curve. Then, if you did the supply experiment, you can explain that in that classroom market, demand was fixed (so there was a vertical demand curve) at the quantity that you had decided to buy. The equilibrium occurred where the market supply curve (supply by the students) intersected your demand curve. Point out that the trades you made in your classroom economy made buyers and sellers better off. If you want to devote a class to equilibrium and the gains from trade in a market, you might want to run a double oral auction. There are lots of descriptions of these and one of the best is at Charlie Holt’s http://veconlab.econ.virginia.edu/admin.htm 4. 價格上漲直至短缺情況消失，並達到市場均衡。

4.3 市場均衡 圖 4.10(b) 達成市場均衡的力量 在價格為 $1.5 / 瓶時， 1. 供給量等於 1,100 萬瓶 2. 需求量等於 900 萬瓶 3. 供給過剩 200 萬瓶 4. 價格下跌，直至過剩情況消失並達到市場均衡。

需求變動的影響 4.3 市場均衡 事例：新的研究認為，自來水是受到污染的。 則這項研究對瓶裝水的影響為： 因為自來水受到污，瓶裝水的需求產生變動 瓶裝水的需求增加，需求曲線右移 則新的均衡價格與均衡數量為何？有什麼改變？

4.3 市場均衡 圖 4.11(a) 需求變動的影響 1. 需求增加，需求曲線右移 2. 在價格為 $1 / 瓶下，產生短缺，因此價格上漲。 3. 供給量延著供給曲線增加 Tell students that they will do much better on the exam if they DRAW the demand-supply graph to answer a question. Show them how much easier it is to see the effects of a change in demand or a change in supply or both on the equilibrium price and equilibrium quantity if they draw the graph. 4. 均衡數量增加

4.3 市場均衡 事例： 無熱量的運動飲料上市 此事件對瓶裝水的影響， 新動運動飲料是瓶裝水的替代品，故瓶裝水的需求產生變動 瓶裝水的需求減少，需求曲線左移 則新的均衡價格及均衡數量為何？有何改變？

4.3 市場均衡 圖 4.11(b) 需求變動的影響 1. 需求減少，需求曲線左移 2. 在價格為 $1 / 瓶時，產生過剩，因此價格下跌 3. 供給量延著供給曲線下滑 Now emphasize the distinction between a change in supply and a change in the quantity supplied. 4. 均衡數量減少

4.3 市場均衡 當需求變動： 供給曲線並無移動 但供給數量會改變 均衡價格與均衡數量則與需求變動方向一致

供給變動的影響 4.3 市場均衡 事例：歐洲國家在美國生產瓶裝水 此事件對瓶裝水的影響， 因為生產瓶裝水的廠商增加，瓶裝水的供給產生變動 瓶裝水的供給增加，則供給曲線右移 則新的均衡價格與均衡數量為何？有何改變？

4.3 市場均衡 圖 4.12(a) 供給變動的影響 1. 供給增加，供給曲線右移 2. 在價格為 $1 / 瓶時，產生過剩，價格下跌 3. 需求量延著需求曲線增加 4. 均衡數量增加.

4.3 市場均衡 事例：乾旱導致泉水枯竭 此事件對瓶裝水的影響， 泉水枯竭導致瓶裝水的供給產生變動 瓶裝水的供給減少，供給曲線左移 則新的均衡價格與均衡數量為何？有何改變？

4.3 市場均衡 圖 4.12(b) 供給變動的影響 1. 供給減少，供給曲線左移 2. 在價格為 $1 / 瓶下，產生短缺，價格上漲 3. 需求量延著需求曲線下滑 4. 均衡數量減少

4.3 市場均衡 當供給變動時， 需求曲線並無移動 但需求量會產生改變 均衡價格與供給變動方向相反 均衡數量與供給變動方向一致

4.3 市場均衡 需求與供給皆增加， 均衡數量增加 均衡價格的變動方向不一定， 需求增加的幅度大於供給，則價格上漲 供給增加的幅度大於需求，則價格下跌

4.3 市場均衡 需求與供給皆減少， 均衡數量減少 均衡價格的變動方向不一定， 需求減少的幅度大於供給，則價格下跌 供給減少的幅度大於需求，則價格上漲

4.3 市場均衡 需求增加與供給減少， 均衡價格上漲 均衡數量的變動方向不一定， 需求增加幅度大於供給減少幅度，則數量增加 供給減少幅度大於需求增加幅度，則數量減少

4.3 市場均衡 需求減少與供給增加 均衡價格下跌 均衡數量的變動方向不一定， 需求減少幅度大於供給增加幅度，則數量減少 供給增加幅度大於需求減少幅度，則數量增加