Thursday, 30 April 2009
Friday, 17 April 2009
問題解答：卷一、卷二及其他
這裡解答一些有關機票減價那道題目的問題，因這些問題可用作示範如何驗證假說 (hypothesis)，有助同學思考。
問題一 by Anonymous ：
forQ9C
if i say there are only a few of first-class seat, the dicount policy will increase the administration cost ( transaction cost ).The transaction cost will rise the average price of the first-class seat in a higher amount .
Also if the cost of adopting the disounting arrangement is higher than the earning of adopting arrangement , then the arrangement wont exist .
由於頭等的座位少, 用 discount 既話會增加交易費用(行政費用), 而基於交易費用會平均攤分比頭等的機票, 所以每張頭等機票的價格會上升, 假如採用discount所賺既earning少過交費成本, 頭等機票便不會有discount
IS IT CORRECT ??
解答：
要實施減價安排，當然需要一些負責票務的人手從事，但經濟客位已有減價的安排，即航空公司已有票務人員從事減價的安排，這些人員熟知價格變動及減價的時間和幅度；為頭等客位減價是無需增設獨立團隊 (team of staff) 然後按經濟客位和頭等客位各自攤分這些成本的。而頭等客位的數量遠少於經濟客位，要就頭等客位減價根本無需多聘甚麼人手（即使多聘人手也不會令平均成本上升）。
問題二 by Anonymous ：
Is it possible to explain the pricing tatics by aruging that given the existence of info cost, lowering the price of first class ticket would mean a poorer service offered to consumers?
解答：
原來的票價固然反映了服務的質素。減價的安排並非劃一將票價調低，而是有空位時作出不同的減幅。這裡涉及的是減價安排，而非劃一調低票價。減價安排會減低服務質素這論點解釋不了為何經濟客位提供減價安排。在減價安排下，不同的服務質素必然存在相應的價格，邏輯上你不能說經濟客位可以在減價安排下有這樣的一個價，而頭等客位則沒有。
另簡覆一些其他問題。
問題三 by Anonymous：
我想問關於第5題，那條題目的意思是指每個國家一單位資源的產出如下，那為什麼題目中的資料是or，而不是and呢?? 我的意思是指，那個題目given的圖表，為什麼不是指在1單位資源下所能夠生產的x and y and z 的的數量，而係x or y or z的數量呢??
question 5 題目既字眼好難分辨到係一單位生產所有物品or只生產到一物品, 以前者既方法計算，就此全軍覆沒？多謝指教。
解答：
從題中的「下表顯示各國使用一單位的投入可生產的產出的數量」及三種物品以三個獨立的欄（separate columns）分列，正常的理解是（就A國而言）一單位的投入可生產的物品X為1，一單位的投入可生產的物品Y為2，一單位的投入可生產的物品Z為 1.5，如此類推。再者，若把物品X、Y及Z的產出理解為一單位的投入同時可生產的物品，題中應附有關於在三種物品之間的投入分配，否則不能計算 (a) 至 (d) 的答案。
（續）問題三 by Anonymous：
多謝阿sir百忙之中抽空回應，但用and仍可以做計到a至d的答案...
以(a)為例依阿sir你理解，是1x or 2y or 1.5z，然後出到(a)部份A國的機會成本資料, 但如果用and的話，就是1x and 2y and 1.5z，即是3x or 6y or 4.5z，同樣地可以出到相同比例的機會成本資料。不過之後b,c,d答案就會三倍化，理解有錯嗎?
再一次多謝阿sir回應...
解答：
若你假設是 AND 的話，你需要假設三國皆平均分配資源才可計算出機會成本及餘下的其他部份。
問題四 by Anonymous：
請問如果第六題, 我寫consumption coupon係增加mpc, 因為consumption coupon令貨品價格下趺, 合理嗎?^^
請問如果第六條, 我寫consumption coupon 影響mpc, 因為價格下趺,mpc上升, 合理嗎??^^
解答：
消費函數是可用收入的函數 (consumption function is a function of disposable income)；而在 Elementary Keynesian Model 中價格是假設為不變的。
另外，有些同學問「評級的問題」一貼中所說的 75 所除的總分是多少。同學是沒有看懂我的文章了。多看一遍吧。
這裡貼上已答覆的問題，方便同學閱讀。
by abbc1332：
For question 6(b)
Do you think that a loss to the employer due to the choice of share contract is a possible answer? I answer it based on 佃農理論 and my final conclusion is that other contract will be chosen by the employer to avoid that part of loss.
For qustion 7(b)
My answer is: A transferable license can lower the information cost of hunter since they are now no need to know fully about their own productivity in advance.(If they found they loss money hunting there, they can simplily sell it to others.)So, with a restrictive supply, the price should gone up as well as the revenue. Is it possible answer?
解答：
Actually there is no need for you to answer the question with "the theory of share tenancy", which could possibly cover issues ranging from the invariance of contractual arrangements (with full consideration of the constraint of competition) to the choice of contracts under different constraints, to the prediction of farming intensity under share restriction, &c., &c. Of course, the choice of contracts subject to TC constraints is always important in AL exam, but before you use any concepts uncovered in the syllabus you must make sure that you understand those concepts accurately. And you would do it better by considering the constraints in different scenarios without confining yourself to something you may have learnt. Anyway, the focus of the question lies more on why factories do not turn to use share contracts to evade the employer-employee relationship (i.e. the problem of using share contract). If you can point out why other contractual arrangements can evade such relationship at a low transaction costs than the share contracts, definitely it's a reasoned answer.
It's unclear what you mean by restrictive supply --- you are probably referring to a fixed quantity. Actually the licence issuing department would sell less licences when the licences are transferable. Don't worry. Most candidates would do the same.
問題一 by Anonymous ：
forQ9C
if i say there are only a few of first-class seat, the dicount policy will increase the administration cost ( transaction cost ).The transaction cost will rise the average price of the first-class seat in a higher amount .
Also if the cost of adopting the disounting arrangement is higher than the earning of adopting arrangement , then the arrangement wont exist .
由於頭等的座位少, 用 discount 既話會增加交易費用(行政費用), 而基於交易費用會平均攤分比頭等的機票, 所以每張頭等機票的價格會上升, 假如採用discount所賺既earning少過交費成本, 頭等機票便不會有discount
IS IT CORRECT ??
解答：
要實施減價安排，當然需要一些負責票務的人手從事，但經濟客位已有減價的安排，即航空公司已有票務人員從事減價的安排，這些人員熟知價格變動及減價的時間和幅度；為頭等客位減價是無需增設獨立團隊 (team of staff) 然後按經濟客位和頭等客位各自攤分這些成本的。而頭等客位的數量遠少於經濟客位，要就頭等客位減價根本無需多聘甚麼人手（即使多聘人手也不會令平均成本上升）。
問題二 by Anonymous ：
Is it possible to explain the pricing tatics by aruging that given the existence of info cost, lowering the price of first class ticket would mean a poorer service offered to consumers?
解答：
原來的票價固然反映了服務的質素。減價的安排並非劃一將票價調低，而是有空位時作出不同的減幅。這裡涉及的是減價安排，而非劃一調低票價。減價安排會減低服務質素這論點解釋不了為何經濟客位提供減價安排。在減價安排下，不同的服務質素必然存在相應的價格，邏輯上你不能說經濟客位可以在減價安排下有這樣的一個價，而頭等客位則沒有。
另簡覆一些其他問題。
問題三 by Anonymous：
我想問關於第5題，那條題目的意思是指每個國家一單位資源的產出如下，那為什麼題目中的資料是or，而不是and呢?? 我的意思是指，那個題目given的圖表，為什麼不是指在1單位資源下所能夠生產的x and y and z 的的數量，而係x or y or z的數量呢??
question 5 題目既字眼好難分辨到係一單位生產所有物品or只生產到一物品, 以前者既方法計算，就此全軍覆沒？多謝指教。
解答：
從題中的「下表顯示各國使用一單位的投入可生產的產出的數量」及三種物品以三個獨立的欄（separate columns）分列，正常的理解是（就A國而言）一單位的投入可生產的物品X為1，一單位的投入可生產的物品Y為2，一單位的投入可生產的物品Z為 1.5，如此類推。再者，若把物品X、Y及Z的產出理解為一單位的投入同時可生產的物品，題中應附有關於在三種物品之間的投入分配，否則不能計算 (a) 至 (d) 的答案。
（續）問題三 by Anonymous：
多謝阿sir百忙之中抽空回應，但用and仍可以做計到a至d的答案...
以(a)為例依阿sir你理解，是1x or 2y or 1.5z，然後出到(a)部份A國的機會成本資料, 但如果用and的話，就是1x and 2y and 1.5z，即是3x or 6y or 4.5z，同樣地可以出到相同比例的機會成本資料。不過之後b,c,d答案就會三倍化，理解有錯嗎?
再一次多謝阿sir回應...
解答：
若你假設是 AND 的話，你需要假設三國皆平均分配資源才可計算出機會成本及餘下的其他部份。
問題四 by Anonymous：
請問如果第六題, 我寫consumption coupon係增加mpc, 因為consumption coupon令貨品價格下趺, 合理嗎?^^
請問如果第六條, 我寫consumption coupon 影響mpc, 因為價格下趺,mpc上升, 合理嗎??^^
解答：
消費函數是可用收入的函數 (consumption function is a function of disposable income)；而在 Elementary Keynesian Model 中價格是假設為不變的。
另外，有些同學問「評級的問題」一貼中所說的 75 所除的總分是多少。同學是沒有看懂我的文章了。多看一遍吧。
這裡貼上已答覆的問題，方便同學閱讀。
by abbc1332：
For question 6(b)
Do you think that a loss to the employer due to the choice of share contract is a possible answer? I answer it based on 佃農理論 and my final conclusion is that other contract will be chosen by the employer to avoid that part of loss.
For qustion 7(b)
My answer is: A transferable license can lower the information cost of hunter since they are now no need to know fully about their own productivity in advance.(If they found they loss money hunting there, they can simplily sell it to others.)So, with a restrictive supply, the price should gone up as well as the revenue. Is it possible answer?
解答：
Actually there is no need for you to answer the question with "the theory of share tenancy", which could possibly cover issues ranging from the invariance of contractual arrangements (with full consideration of the constraint of competition) to the choice of contracts under different constraints, to the prediction of farming intensity under share restriction, &c., &c. Of course, the choice of contracts subject to TC constraints is always important in AL exam, but before you use any concepts uncovered in the syllabus you must make sure that you understand those concepts accurately. And you would do it better by considering the constraints in different scenarios without confining yourself to something you may have learnt. Anyway, the focus of the question lies more on why factories do not turn to use share contracts to evade the employer-employee relationship (i.e. the problem of using share contract). If you can point out why other contractual arrangements can evade such relationship at a low transaction costs than the share contracts, definitely it's a reasoned answer.
It's unclear what you mean by restrictive supply --- you are probably referring to a fixed quantity. Actually the licence issuing department would sell less licences when the licences are transferable. Don't worry. Most candidates would do the same.
Monday, 13 April 2009
2009 高考經濟學 卷二 B & C 參考答案
本想早點完成卷二的參考答案，奈何工作繁多，又因本年的卷二題目較簡單直接，同學的爭議較少，擱下來了便遲遲未動筆。中文版將稍後發布，請同學耐心等待。
(b) False. With an expectation-augmented Phillips curve, if the actual rate of inflation is lower than the expected rate, cyclical unemployment will be positive, i.e. cyclical unemployment coexists with inflation. Inflation, when fully anticipated, can coexist with natural unemployment.
(c) False. It would be generally more difficult to turn water into other goods and services at short notice without incurring loss, as in normal situations travelers would equip themselves with enough water and therefore water would not be easily marketable. (Given that money is a generally accepted medium of exchange and a better store of value, money is still the most liquid asset even in the Sahara Desert.)
(d) False. A fixed exchange rate system could not be maintained if the central bank does not have enough foreign exchange reserves to keep its currency at the target value. In terms of stability of exchange rate, under a fixed exchange rate system with a currency band, the exchange rate of a currency may fluctuate within the currency band while under a flexible exchange rate system the market exchange rate can be rather stable if there is no wild fluctuations in the demand for and supply of the currency, or if the effects of the fluctuations in the demand for and supply of the currency on the exchange rate offset each other.
Question 2
(a) Inclusive of the principal, the real interest rate is the price of goods today in terms of goods tomorrow.
(b) Inclusive of the principal, the nominal interest rate is the price of money today in terms of money tomorrow.
(c) Nominal interest rate is equal to the sum of the real interest rate and the anticipated inflation rate. The inflation rate is expected (or ex ante) because the actual inflation rate is not realized at the time when the nominal interest rate is determined.
(d) If we interpret money as a non-interest-bearing asset, the nominal interest rate, being the return on holding other interest-bearing assets, is the cost of holding money. The nominal interest rate in this case is equal to the interest differential between the return on other interest-bearing assets and money, and the nominal interest differential is equal to the real interest differential. In the case of money being an interest-bearing asset, the nominal interest differential is still equal to the real interest differential, and both can be interpreted as the cost of holding money.
Question 3
(a) In equilibrium, Y = C + I + G for a closed economy, and therefore Y − C − G = I. National saving (S = Y − C − G), representing the part of output not consumed by the households and the governments, would be equal to investment.
(b) Real investment is equated to national saving in a closed economy because both investment and saving are decisions related to real resources (investment referring to the accumulation of capital goods while saving referring to output not consumed by the households and the government).
(c)(i) In equilibrium, Y = C + I + G + NX for an open economy, and therefore Y − C − G − I = NX. (S − I) equals NX.
(ii) The excess of domestic investment over national saving would be financed by net imports (NX <>), which can be viewed a net capital inflow (recall the balance of payment condition of NX = −KFA).
(d) A high consumption country would tend to have a low level of national saving. Given the condition of (S − I) = NX and a certain level of I, it is more likely that S falls below I, resulting in a trade deficit (NX <>).
Section C
Question 4
(a) A liquidity trap means the situation where the interest rate reaches a sufficiently low level and the opportunity cost of holding money (the return on other interest-bearing assets) is so low that people would hold money (as an asset providing liquidity) rather than other interest-bearing assets, which are likely to incur capital loss to their holders. The money demand curve will be perfectly interest elastic (with a horizontal portion at the existing interest rate).
(b) Under a liquidity trap, an increase in income (Y) and therefore the transaction demand for money would be offset by a corresponding decrease in asset demand for money at the existing interest rate (or an infinitesimally small increase in the interest rate).
An increase in money supply by the central bank would not lead to a fall in interest rate because the newly printed money would be translated into money demanded for asset purpose at the going interest rate, therefore would not be able to stimulate output.
(c) When interest rate is used as the policy instrument, an increase in income (Y) and therefore the transaction demand for money, given a downward sloping money demand curve without the perfectly interest elastic portion, would have to be accompanied by a corresponding increase in money supply by the central bank so that the equilibrium interest rate remains at the target level.
(d) The central bank would be able to lower the interest rate, but given the perfectly interest-elastic money demand it will result in money market disequilibrium. Therefore, in the context of money market equilibrium central bank could not lower the interest rate. If a liquidity trap occurs at the zero lower bound of interest rate, the interest rate could not be lowered, irrespective of whether money market equilibrium is considered.
Question 5
(a)(i)
In country A, the opportunity cost of producing
1X = 2Y or 1.5Z ; 1Y = 0.5X or 0.75Z ; 1Z = 2/3X or 4/3Y
In country B, the opportunity cost of producing
1X = 2/3Y or 2Z ; 1Y = 1.5X or 3Z ; 1Z = 0.5X or 1/3Y
In country C, the opportunity cost of producing
1X = 0.625Y or 1.5Z ; 1Y = 1.6X or 2.4Z ; 1Z = 2/3X or 5/12Y
(ii)
Comparative advantage
Good X: country C ; Good Y: country A ; Good Z: country B
(b)
Total world production under autarky
Good X: 8 units ; Good Y: 6.5 units ; Good Z: 13.5 units
(c)
Total world production under complete specialization
Good X: 12 units ; Good Y: 6 units ; Good Z: 18 units
(d)(i)
Consumption for each country
Good X: 4 units ; Good Y: 2 units ; Good Z: 6 units
Both country A and B will gain (country A consumes the same quantity of Good Y but a larger quantity of Good X and Z, and country B consumes the same quantity of Good Y and Z but a larger quantity of Good X). Country C will lose (it consumes the same quantity of Good X and Z but a smaller quantity of Good Y).
(ii)
The winner(s) (A and/or B) has/have to compensate at least 0.8X to C (country C’s opportunity cost of producing 0.5Y = 0.8X).
Question 6
(由於此題包含符號，只能以圖片上載，同學按下圖片便能看得清楚。)
The answers provided hereunder offer only the correct approach to the questions, rather than the points that should be included in the examination for scoring marks. Readers should not simply evaluate their scores in the live examination on this basis (Readers in general may not know why it is so, although my students would definitely understand what I mean.)
Section B
Question 1
Section B
Question 1
(a) False. The importation of workers from abroad will increase a country’s GDP only if there is no worker displacement or in the presence of worker displacement the productivity of imported workers are higher than the displaced workers. If the productivity of imported workers is lower than that of the displaced workers, the country’s GDP will fall. The first part of the statement is correct though, because GNP will decrease (increase) if the imported workers work for a period shorter than one year and their contribution to GDP, measured by marginal productivity, is smaller (larger) than the wage payments they earn in the economy, even in the absence of worker displacement.
(b) False. With an expectation-augmented Phillips curve, if the actual rate of inflation is lower than the expected rate, cyclical unemployment will be positive, i.e. cyclical unemployment coexists with inflation. Inflation, when fully anticipated, can coexist with natural unemployment.
(c) False. It would be generally more difficult to turn water into other goods and services at short notice without incurring loss, as in normal situations travelers would equip themselves with enough water and therefore water would not be easily marketable. (Given that money is a generally accepted medium of exchange and a better store of value, money is still the most liquid asset even in the Sahara Desert.)
(d) False. A fixed exchange rate system could not be maintained if the central bank does not have enough foreign exchange reserves to keep its currency at the target value. In terms of stability of exchange rate, under a fixed exchange rate system with a currency band, the exchange rate of a currency may fluctuate within the currency band while under a flexible exchange rate system the market exchange rate can be rather stable if there is no wild fluctuations in the demand for and supply of the currency, or if the effects of the fluctuations in the demand for and supply of the currency on the exchange rate offset each other.
Question 2
(a) Inclusive of the principal, the real interest rate is the price of goods today in terms of goods tomorrow.
(b) Inclusive of the principal, the nominal interest rate is the price of money today in terms of money tomorrow.
(c) Nominal interest rate is equal to the sum of the real interest rate and the anticipated inflation rate. The inflation rate is expected (or ex ante) because the actual inflation rate is not realized at the time when the nominal interest rate is determined.
(d) If we interpret money as a non-interest-bearing asset, the nominal interest rate, being the return on holding other interest-bearing assets, is the cost of holding money. The nominal interest rate in this case is equal to the interest differential between the return on other interest-bearing assets and money, and the nominal interest differential is equal to the real interest differential. In the case of money being an interest-bearing asset, the nominal interest differential is still equal to the real interest differential, and both can be interpreted as the cost of holding money.
Question 3
(a) In equilibrium, Y = C + I + G for a closed economy, and therefore Y − C − G = I. National saving (S = Y − C − G), representing the part of output not consumed by the households and the governments, would be equal to investment.
(b) Real investment is equated to national saving in a closed economy because both investment and saving are decisions related to real resources (investment referring to the accumulation of capital goods while saving referring to output not consumed by the households and the government).
(c)(i) In equilibrium, Y = C + I + G + NX for an open economy, and therefore Y − C − G − I = NX. (S − I) equals NX.
(ii) The excess of domestic investment over national saving would be financed by net imports (NX <>), which can be viewed a net capital inflow (recall the balance of payment condition of NX = −KFA).
(d) A high consumption country would tend to have a low level of national saving. Given the condition of (S − I) = NX and a certain level of I, it is more likely that S falls below I, resulting in a trade deficit (NX <>).
Section C
Question 4
(a) A liquidity trap means the situation where the interest rate reaches a sufficiently low level and the opportunity cost of holding money (the return on other interest-bearing assets) is so low that people would hold money (as an asset providing liquidity) rather than other interest-bearing assets, which are likely to incur capital loss to their holders. The money demand curve will be perfectly interest elastic (with a horizontal portion at the existing interest rate).
(b) Under a liquidity trap, an increase in income (Y) and therefore the transaction demand for money would be offset by a corresponding decrease in asset demand for money at the existing interest rate (or an infinitesimally small increase in the interest rate).
An increase in money supply by the central bank would not lead to a fall in interest rate because the newly printed money would be translated into money demanded for asset purpose at the going interest rate, therefore would not be able to stimulate output.
(c) When interest rate is used as the policy instrument, an increase in income (Y) and therefore the transaction demand for money, given a downward sloping money demand curve without the perfectly interest elastic portion, would have to be accompanied by a corresponding increase in money supply by the central bank so that the equilibrium interest rate remains at the target level.
(d) The central bank would be able to lower the interest rate, but given the perfectly interest-elastic money demand it will result in money market disequilibrium. Therefore, in the context of money market equilibrium central bank could not lower the interest rate. If a liquidity trap occurs at the zero lower bound of interest rate, the interest rate could not be lowered, irrespective of whether money market equilibrium is considered.
Question 5
(a)(i)
In country A, the opportunity cost of producing
1X = 2Y or 1.5Z ; 1Y = 0.5X or 0.75Z ; 1Z = 2/3X or 4/3Y
In country B, the opportunity cost of producing
1X = 2/3Y or 2Z ; 1Y = 1.5X or 3Z ; 1Z = 0.5X or 1/3Y
In country C, the opportunity cost of producing
1X = 0.625Y or 1.5Z ; 1Y = 1.6X or 2.4Z ; 1Z = 2/3X or 5/12Y
(ii)
Comparative advantage
Good X: country C ; Good Y: country A ; Good Z: country B
(b)
Total world production under autarky
Good X: 8 units ; Good Y: 6.5 units ; Good Z: 13.5 units
(c)
Total world production under complete specialization
Good X: 12 units ; Good Y: 6 units ; Good Z: 18 units
(d)(i)
Consumption for each country
Good X: 4 units ; Good Y: 2 units ; Good Z: 6 units
Both country A and B will gain (country A consumes the same quantity of Good Y but a larger quantity of Good X and Z, and country B consumes the same quantity of Good Y and Z but a larger quantity of Good X). Country C will lose (it consumes the same quantity of Good X and Z but a smaller quantity of Good Y).
(ii)
The winner(s) (A and/or B) has/have to compensate at least 0.8X to C (country C’s opportunity cost of producing 0.5Y = 0.8X).
Question 6
(由於此題包含符號，只能以圖片上載，同學按下圖片便能看得清楚。)
Friday, 10 April 2009
評級的問題
在電郵和網誌中都收到不少同學的問題，很多是有關評級的，例如多少分可拿到 A / B / C。很明白同學非常關心自己的成績，想知道自己大概會得到甚麼 grade，這裡作一點回應。
同學問，過往各等級的分數屬於機密資料，不能公開，那估計今年的分數可以嗎？從事這些工作多年，估計不同等級的分數當然沒有難度，問題是，假如我對你說 75 分能得 A，55 分能得 C，你知道 75 分和 55 分是甚麼意思嗎？我這樣給出一個分數，也許會令同學錯誤估計自己的等級，因為你心目中的 75 分，與現實考試中的 75 分是可以很不同的。
試卷的深淺程度，改卷時的寬緊，還有其他的因素，都會影響分數。一條看似顯淺的題目，你有九成把握，並不必然代表你能拿到九成的分數。一條你毫無頭緒的題目，但你寫了一些自己認為合理的答案，分數亦不一定很低。考生的答案五花八門，哪些答案可以得到較高分數，哪些較低，資深的閱卷員可以判斷得到，但一個考生很難為自己的答案作出準確的判斷。如果我說，就今年的題目而言 75 分可以拿 A，那是基於我對題目的深淺及一貫評卷的寬緊作出的估計，但你對自己分數的估計與我的不同，差異可能很大，若你是我的學生，差異可能小一點，但你的估計也不一定與我相同。
這也是我在參考答案中加上一段解說的原因（當然，同學大多會跳過這段文字，直接看答案去也）。參考答案只為讓同學知道每條題目的重點及正確的思考方向，嘗試滿足同學試後的求知慾，不要把它當成 marking scheme。不要再反覆思考自己錯了甚麼，對了甚麼，每晚睡不好，只會影響往後的考試。
往事已矣，努力向前吧！
同學問，過往各等級的分數屬於機密資料，不能公開，那估計今年的分數可以嗎？從事這些工作多年，估計不同等級的分數當然沒有難度，問題是，假如我對你說 75 分能得 A，55 分能得 C，你知道 75 分和 55 分是甚麼意思嗎？我這樣給出一個分數，也許會令同學錯誤估計自己的等級，因為你心目中的 75 分，與現實考試中的 75 分是可以很不同的。
試卷的深淺程度，改卷時的寬緊，還有其他的因素，都會影響分數。一條看似顯淺的題目，你有九成把握，並不必然代表你能拿到九成的分數。一條你毫無頭緒的題目，但你寫了一些自己認為合理的答案，分數亦不一定很低。考生的答案五花八門，哪些答案可以得到較高分數，哪些較低，資深的閱卷員可以判斷得到，但一個考生很難為自己的答案作出準確的判斷。如果我說，就今年的題目而言 75 分可以拿 A，那是基於我對題目的深淺及一貫評卷的寬緊作出的估計，但你對自己分數的估計與我的不同，差異可能很大，若你是我的學生，差異可能小一點，但你的估計也不一定與我相同。
這也是我在參考答案中加上一段解說的原因（當然，同學大多會跳過這段文字，直接看答案去也）。參考答案只為讓同學知道每條題目的重點及正確的思考方向，嘗試滿足同學試後的求知慾，不要把它當成 marking scheme。不要再反覆思考自己錯了甚麼，對了甚麼，每晚睡不好，只會影響往後的考試。
往事已矣，努力向前吧！
Thursday, 9 April 2009
管理員通告：
昨天考評局發出聲明，刪除卷二MC第七及第八題。詳情見：
http://www.hkeaa.edu.hk/DocLibrary/HKALE/news/press_20090408_statement_chi.pdf
http://www.hkeaa.edu.hk/DocLibrary/HKALE/news/press_20090408_statement_chi.pdf
Wednesday, 8 April 2009
管理員通告：提問和回覆
各位同學：
管理員上
自本網誌建立後，Cliff Yeung 從電郵及本網誌收到大量有關考試的提問，看見同學對自己的前途著緊，又對經濟學如此熱衷，Cliff Yeung 表示感到欣慰。惟由於 Cliff Yeung 時間有限，無法回覆所有同學的提問，只能按提問的深度和價值選擇性作出回應，這裡為沒有得到回覆的同學致歉。Cliff Yeung 鼓勵同學多與朋輩討論經濟學問題，多觀察周遭經濟現象並加以分析，必能有所獲益。
管理員上
Monday, 6 April 2009
2009 高考經濟學 卷一 B & C 參考答案
Section B
The answers provided hereunder offer only the correct approach to the questions, rather than the points that should be included in the examination for scoring marks. Readers should not simply evaluate their scores in the live examination on this basis (Readers in general may not know why it is so, although my students would definitely understand what I mean.)
Question 1
Economics explain behaviour by deriving testable implications from postulates, which restrains human behaviour. The law of demand restrains behaviour in the way that the quantity demanded for a good depends negatively on the price of that good. Without such restraints on human behaviour, no testable implications can be derived. (Students may discuss a little the relationship between the law of demand and the postulate of constrained maximization.)
The demand curve derived from the indifference curve analysis can be downward or upward sloping, given the Giffen good possibility. The law of demand is therefore itself an assertion, requiring no support by the indifference curve analysis.
Question 2
The law of diminishing returns states that as variable factors are continuously added to a given quantity of fixed factor, marginal product will eventually diminish. With a downward sloping marginal product curve of labour (which can be translated into the demand curve for labour), wages and rents can be determined given the upward sloping labour supply curve. Without this law, adding fertilizers to a tiny piece of land would be able to grow enough food to feed the whole world, and in this case land rents (or land price) and wages cannot be determined.
Question 3
A public good is a good that can be consumed concurrently by many individuals. Performance by a pianist and television programmes are examples of public goods privately produced. Private producers can survive if the cost of excluding free-riders is lower than what they can receive from the buyers of the goods. In the context of the above examples, admission fees can be charged for the performance in a concert hall and subscriptions fees for cable TV are routinely charged with a sufficiently low cost of enforcing against free-riders.
Question 4
For a scarce resource with no alternative use, the cost of using the resource would be what the user can obtain from an outright transfer of the resource (or renting the resource to the others). In the late George Stigler’s example of airport built on a small island in the Pacific, there is no other valuable use than airplane refueling. If the owner of that airport chooses to operate it on its own, his cost will be the price he can receive from the outright transfer (or the rent from operating the airport). A cost is implied when there is choice. Operating the airport or renting it out is itself a choice, let alone the choices of different ways of operating the airport, for example, the runways used for airplane landing and taking off.
Question 5
Wealth is income discounted (W=Y/r). Multiplying wealth by the market rate of interest yields (annuity) income, which is the potential consumption that can be made without trenching wealth. In a one-man economy there is no market of any kind, and therefore wealth cannot be determined without the market rate of interest used for discounting, although income exists in a one-man economy.
Section C
Question 6
(a) Adopting piece-rate contracts may render minimum wage laws ineffective because wage rate are measured by piece count instead of the length of working time. The complications are that if the incomes, expressed in terms of hours, of some piece-rate workers with exceptionally low productivities are lower than minimum wage, it may be regarded as a contravention of the law. If such situation results in an abolition of the piece-rate contracts by legislation (as in some western countries), piece-rate contracts would not render the minimum wage laws ineffective. Of course, if production orders are simply sub-contracted with a price set for each unit of the output produced (also a piece-rate contract) to workers who simply work at home, no employer-employee relationship is present and the laws do not apply.
(b) Huge transaction costs are involved in determining the shares of each worker, resolving disputes, and monitoring against underreports of the actual sales.
(c) They are not unemployed if they turn to be self-employed, which may takes various forms like hawking and begging, or if they simply take leisure and do not search for a job.
Question 7
(a) The out-of-state hunters would be better hunters (i.e. hunting more animals) with higher productivity of hunting, as reflected in their higher cost of hunting (e.g. higher licence fee and transportation cost). Given a higher lump-sum cost to be incurred, the average cost of hunting will be lower with more animals hunted and the out-of-state hunters would tend to put more effort to hunt more as well.
(b) More wildlife would be hunted because the licences would more likely be used by better hunters, and the average number of use for each licence would also increase.
Assuming the licence issuing department is maximizing wealth (as it is the case because in the US the licence issuing departments earn commissions from issuing licence), the total licence fees collected would decrease. Transferable licence implies a decrease in the total number of licence issued and an increase in the licence fee for each licence. There exists a combination of price and quantity of licence that makes the total licence fee identical in the two cases. Yet the cost involved in transferring the licence would have to be deducted from the licence fee that could be charged by the licence issuing department under transferable licence, implying a decrease in total licence fee. (Students need not feel disappointed if they could not get this part of the answer because it involves really sophisticated analysis. Alternative answers would be accepted as long as they are well reasoned with appropriate assumptions.)
(c) Preserving wild salmon generates benefits to special interest groups such as the holders of restrictive fishing licences. An increase in the supply of salmon due to private raising of it would reduce the market value of the fishing licences, and hurt the interest of the above interest groups. (Students may tend to think those who fought to preserve wild salmon are environmental protection groups. However, scientifically we cannot distinguish who are truly “environmental protectionists”.)
Question 8
(a) If flights with different flying time (and different vacancy rates) are charged different prices, and the pricing arrangements are open to all passengers (i.e. passengers choose their own flights among those flights with different flying time and prices), there is no price discrimination. If for the same flight with the same flying time (and identical vacancy rate) different discounts are offered to different passengers, it is price discrimination. In the presence of information cost (for both passengers and the airlines) this discounting practice for economy-class tickets would increase the average price received by the airlines, as the ticket prices of flights with better flying time (a higher market demand) will have a higher price when the passengers choose their own flights, while the flights with inferior flying time (a lower market demand) would be fully filled up by offering varying discounts (the marginal cost of serving an additional passenger will be zero when there is vacancy).
(b) Of course higher total revenue. A high uniform price may result in a high vacancy rate while a low uniform price would result in loss in revenue from charging higher prices for some passengers with higher information cost. The discounting practice allows a higher price charged on passengers with higher information cost while generates extra revenue from fully filling up the vacant seats by offering different discounts.
(c) If the first-class tickets offer discounts, some economy-class passengers may switch to buy first-class tickets, resulting in an increase in vacancy for the economy-class seats. The existing discounts for economy-class tickets could not be sustained without a downward adjustment of the discounts. Given that the existing price differential between first-class and economy-class tickets reflects the difference in seat quality and that the seats are already fully occupied under the current discounts adopted for economy-class, a reduction in the prices of the first-class tickets (and therefore the prices of economy-class tickets) would necessarily result in lower revenue.
The answers provided hereunder offer only the correct approach to the questions, rather than the points that should be included in the examination for scoring marks. Readers should not simply evaluate their scores in the live examination on this basis (Readers in general may not know why it is so, although my students would definitely understand what I mean.)
Question 1
Economics explain behaviour by deriving testable implications from postulates, which restrains human behaviour. The law of demand restrains behaviour in the way that the quantity demanded for a good depends negatively on the price of that good. Without such restraints on human behaviour, no testable implications can be derived. (Students may discuss a little the relationship between the law of demand and the postulate of constrained maximization.)
The demand curve derived from the indifference curve analysis can be downward or upward sloping, given the Giffen good possibility. The law of demand is therefore itself an assertion, requiring no support by the indifference curve analysis.
Question 2
The law of diminishing returns states that as variable factors are continuously added to a given quantity of fixed factor, marginal product will eventually diminish. With a downward sloping marginal product curve of labour (which can be translated into the demand curve for labour), wages and rents can be determined given the upward sloping labour supply curve. Without this law, adding fertilizers to a tiny piece of land would be able to grow enough food to feed the whole world, and in this case land rents (or land price) and wages cannot be determined.
Question 3
A public good is a good that can be consumed concurrently by many individuals. Performance by a pianist and television programmes are examples of public goods privately produced. Private producers can survive if the cost of excluding free-riders is lower than what they can receive from the buyers of the goods. In the context of the above examples, admission fees can be charged for the performance in a concert hall and subscriptions fees for cable TV are routinely charged with a sufficiently low cost of enforcing against free-riders.
Question 4
For a scarce resource with no alternative use, the cost of using the resource would be what the user can obtain from an outright transfer of the resource (or renting the resource to the others). In the late George Stigler’s example of airport built on a small island in the Pacific, there is no other valuable use than airplane refueling. If the owner of that airport chooses to operate it on its own, his cost will be the price he can receive from the outright transfer (or the rent from operating the airport). A cost is implied when there is choice. Operating the airport or renting it out is itself a choice, let alone the choices of different ways of operating the airport, for example, the runways used for airplane landing and taking off.
Question 5
Wealth is income discounted (W=Y/r). Multiplying wealth by the market rate of interest yields (annuity) income, which is the potential consumption that can be made without trenching wealth. In a one-man economy there is no market of any kind, and therefore wealth cannot be determined without the market rate of interest used for discounting, although income exists in a one-man economy.
Section C
Question 6
(a) Adopting piece-rate contracts may render minimum wage laws ineffective because wage rate are measured by piece count instead of the length of working time. The complications are that if the incomes, expressed in terms of hours, of some piece-rate workers with exceptionally low productivities are lower than minimum wage, it may be regarded as a contravention of the law. If such situation results in an abolition of the piece-rate contracts by legislation (as in some western countries), piece-rate contracts would not render the minimum wage laws ineffective. Of course, if production orders are simply sub-contracted with a price set for each unit of the output produced (also a piece-rate contract) to workers who simply work at home, no employer-employee relationship is present and the laws do not apply.
(b) Huge transaction costs are involved in determining the shares of each worker, resolving disputes, and monitoring against underreports of the actual sales.
(c) They are not unemployed if they turn to be self-employed, which may takes various forms like hawking and begging, or if they simply take leisure and do not search for a job.
Question 7
(a) The out-of-state hunters would be better hunters (i.e. hunting more animals) with higher productivity of hunting, as reflected in their higher cost of hunting (e.g. higher licence fee and transportation cost). Given a higher lump-sum cost to be incurred, the average cost of hunting will be lower with more animals hunted and the out-of-state hunters would tend to put more effort to hunt more as well.
(b) More wildlife would be hunted because the licences would more likely be used by better hunters, and the average number of use for each licence would also increase.
Assuming the licence issuing department is maximizing wealth (as it is the case because in the US the licence issuing departments earn commissions from issuing licence), the total licence fees collected would decrease. Transferable licence implies a decrease in the total number of licence issued and an increase in the licence fee for each licence. There exists a combination of price and quantity of licence that makes the total licence fee identical in the two cases. Yet the cost involved in transferring the licence would have to be deducted from the licence fee that could be charged by the licence issuing department under transferable licence, implying a decrease in total licence fee. (Students need not feel disappointed if they could not get this part of the answer because it involves really sophisticated analysis. Alternative answers would be accepted as long as they are well reasoned with appropriate assumptions.)
(c) Preserving wild salmon generates benefits to special interest groups such as the holders of restrictive fishing licences. An increase in the supply of salmon due to private raising of it would reduce the market value of the fishing licences, and hurt the interest of the above interest groups. (Students may tend to think those who fought to preserve wild salmon are environmental protection groups. However, scientifically we cannot distinguish who are truly “environmental protectionists”.)
Question 8
(a) If flights with different flying time (and different vacancy rates) are charged different prices, and the pricing arrangements are open to all passengers (i.e. passengers choose their own flights among those flights with different flying time and prices), there is no price discrimination. If for the same flight with the same flying time (and identical vacancy rate) different discounts are offered to different passengers, it is price discrimination. In the presence of information cost (for both passengers and the airlines) this discounting practice for economy-class tickets would increase the average price received by the airlines, as the ticket prices of flights with better flying time (a higher market demand) will have a higher price when the passengers choose their own flights, while the flights with inferior flying time (a lower market demand) would be fully filled up by offering varying discounts (the marginal cost of serving an additional passenger will be zero when there is vacancy).
(b) Of course higher total revenue. A high uniform price may result in a high vacancy rate while a low uniform price would result in loss in revenue from charging higher prices for some passengers with higher information cost. The discounting practice allows a higher price charged on passengers with higher information cost while generates extra revenue from fully filling up the vacant seats by offering different discounts.
(c) If the first-class tickets offer discounts, some economy-class passengers may switch to buy first-class tickets, resulting in an increase in vacancy for the economy-class seats. The existing discounts for economy-class tickets could not be sustained without a downward adjustment of the discounts. Given that the existing price differential between first-class and economy-class tickets reflects the difference in seat quality and that the seats are already fully occupied under the current discounts adopted for economy-class, a reduction in the prices of the first-class tickets (and therefore the prices of economy-class tickets) would necessarily result in lower revenue.
2009 高考經濟學選擇題排難
本來不打算寫這 MC 排難，但同學對我說他們為 MC 題目憂心，多番要求解說，又因為我早前出的 MC 答案有排版錯誤，引起了混亂，令同學作出不必要的爭拗，多少浪費了同學的寶貴時間，現在為表歉意，也應該就幾題較多爭議的 MC 作出解釋，減低大家的交易費用，算是一點補償。
同學得知我要這樣做，問道：「公開這些解說，不怕受打手攻擊嗎？」我的回答是，從事考評工 作多年，當時寫試後報告也會受到質疑，但只要邏輯井然，沒有甚麼可怕的地方。我也習慣了回應老師的提問。我想，試試以非官方身份寫一份選擇題的試後報告 吧！趁着同學記憶猶新，也許比幾個月後才出版的官方報告對同學更有幫助。
Paper 1
Option A is definitely true while option D is only conditionally true. Therefore, option A is the best answer.
Q5
It’s tempting to choose C for this question, as utility maximization often results in tautological statements. Yet given option D, none of the above would be the best answer because utility maximization can still derive testable implication, though very limited in application. For example, the apparent-real-income-constant demand curve derived from utility maximization (subject to changes in budget constraints) is definitely downward sloping, and therefore testable implications can be derived. In this case, of course, the application is very limited, as we seldom observe a reduction in price being accompanied by an extraction of money income in a way that makes the original bundle just affordable (but it is undeniable that it can be tested).
Q26
Both Option B and option D seem to be reasonable answers.
Option B: Highway owners definitely would not act against overloading if the cost of monitoring against it is really prohibitively high. However, such cost need not be that huge. For example, checkpoints with one or two weight-checking equipments could simply be set at the toll booths (if you have been on the highways in China, you will know that serious overloading is not difficult to detect — those vehicles move so slowly that you might think they are coming to a stop), and with such checkpoints vehicles would tend more to restrain themselves from overloading.
Option D: Instead of focusing only on the cost of monitoring, this option takes into account the costs as well as the benefits of allowing overloading, a voluntary choice made by the owners of private highways. Overloading incurs repair cost to those owners, yet if the owners are able to charge a higher toll that could more than compensate the repair cost, allowing overloading would be better than monitoring against it and it makes no sense to eliminate overloading by paying an additional cost of monitoring. Students with a sharp mind would come up with this inference: the penalty that could potentially be collected from such monitoring could simply be charged in disguise through a higher toll without doing any monitoring work when overloading is so prevalent. (Imposing a penalty would be what the owners could do with monitoring because putting the drivers in jail does not generate any benefits to the highway operators.)
Q29
Students may wonder which version of the Coase Theorem is relevant for this question. As stated in the question (different assignment of rights will result in the same, as well as efficient, resource allocation), it would be the invariance theorem, though zero TC is not mentioned. (The useful version is the delineation of rights is an essential prelude for market transaction.)
If transaction costs are really zero, thievery would simply not occur (it makes no sense to steal from others because it must be discovered and people can enforce against thievery at no cost). [If you have chosen C as the answer, you may like to argue that thievery then does no harm to society because it will not happen altogether, but it wouldn’t make it a better answer than option D.]
In the presence of transaction costs, thievery does harm to the society in that it leads to an increase in transaction costs (locks and security systems are transaction costs).
Q30
Many students tend to choose Option A, because the phrase “prohibitively high” seems to be a sensible explanation. But it doesn’t make much sense actually.
Option A: If the cost of checking blood quality is prohibitively high, blood donated would not have been FOUND to be more prone to disease. (If the blood donated is found to be diseased, it means blood quality can be, and has been checked.) The statement is itself inconsistent with the observation from the stem of the question.
Option B: Economics does not explain why people engage in charity behaviour, e.g. blood donation. Rather, it explains how such behaviour differs under different constraints. People will tend to engage less intensively in blood donation if the cost of doing so is higher or if the return is lower. Assuming a constant preference of charity behaviour (we cannot explain behaviour by preference or taste), in the case of blood donated for free, there is no pecuniary return on donating blood, and the non-pecuniary benefit to blood donors is zero as well if they know their blood is medically dangerous. Therefore, they would tend not to donate their blood.
本年 Paper 2 較有爭議的只有一條，解釋如下：
Paper 2
Q27
The only doubt in this question is whether option (3) is correct. It is NOT correct because PPP is a long-term concept, and it does not imply equalization of prices in terms of a given currency at any point of time. (Arbitrage takes time to restore the PPP condition.)
同學得知我要這樣做，問道：「公開這些解說，不怕受打手攻擊嗎？」我的回答是，從事考評工 作多年，當時寫試後報告也會受到質疑，但只要邏輯井然，沒有甚麼可怕的地方。我也習慣了回應老師的提問。我想，試試以非官方身份寫一份選擇題的試後報告 吧！趁着同學記憶猶新，也許比幾個月後才出版的官方報告對同學更有幫助。
Remarks on AL Econ 2009 Selected MC Questions
Paper 1
Q1
Students may find it a struggle choosing between option A and D.
Option D: Scarcity does not imply competition in a one-man economy.
Students may find it a struggle choosing between option A and D.
Option D: Scarcity does not imply competition in a one-man economy.
Option A: When there is shortage, it means the criterion relevant for resolving competition is not specified (and therefore no refutable implications can be derived). In this sense, shortage implies competition because, without competition, it makes no sense to talk about specifying the criteria determining winners and losers, and with competition there must be scarcity. Though shortage does not exist if the criterion relevant for resolving competition is specified, it doesn’t matter for the above conclusion because this question is not about under what condition shortage will or will not occur.
Option A is definitely true while option D is only conditionally true. Therefore, option A is the best answer.
Q5
It’s tempting to choose C for this question, as utility maximization often results in tautological statements. Yet given option D, none of the above would be the best answer because utility maximization can still derive testable implication, though very limited in application. For example, the apparent-real-income-constant demand curve derived from utility maximization (subject to changes in budget constraints) is definitely downward sloping, and therefore testable implications can be derived. In this case, of course, the application is very limited, as we seldom observe a reduction in price being accompanied by an extraction of money income in a way that makes the original bundle just affordable (but it is undeniable that it can be tested).
Q26
Both Option B and option D seem to be reasonable answers.
Option B: Highway owners definitely would not act against overloading if the cost of monitoring against it is really prohibitively high. However, such cost need not be that huge. For example, checkpoints with one or two weight-checking equipments could simply be set at the toll booths (if you have been on the highways in China, you will know that serious overloading is not difficult to detect — those vehicles move so slowly that you might think they are coming to a stop), and with such checkpoints vehicles would tend more to restrain themselves from overloading.
Option D: Instead of focusing only on the cost of monitoring, this option takes into account the costs as well as the benefits of allowing overloading, a voluntary choice made by the owners of private highways. Overloading incurs repair cost to those owners, yet if the owners are able to charge a higher toll that could more than compensate the repair cost, allowing overloading would be better than monitoring against it and it makes no sense to eliminate overloading by paying an additional cost of monitoring. Students with a sharp mind would come up with this inference: the penalty that could potentially be collected from such monitoring could simply be charged in disguise through a higher toll without doing any monitoring work when overloading is so prevalent. (Imposing a penalty would be what the owners could do with monitoring because putting the drivers in jail does not generate any benefits to the highway operators.)
Q29
Students may wonder which version of the Coase Theorem is relevant for this question. As stated in the question (different assignment of rights will result in the same, as well as efficient, resource allocation), it would be the invariance theorem, though zero TC is not mentioned. (The useful version is the delineation of rights is an essential prelude for market transaction.)
If transaction costs are really zero, thievery would simply not occur (it makes no sense to steal from others because it must be discovered and people can enforce against thievery at no cost). [If you have chosen C as the answer, you may like to argue that thievery then does no harm to society because it will not happen altogether, but it wouldn’t make it a better answer than option D.]
In the presence of transaction costs, thievery does harm to the society in that it leads to an increase in transaction costs (locks and security systems are transaction costs).
Q30
Many students tend to choose Option A, because the phrase “prohibitively high” seems to be a sensible explanation. But it doesn’t make much sense actually.
Option A: If the cost of checking blood quality is prohibitively high, blood donated would not have been FOUND to be more prone to disease. (If the blood donated is found to be diseased, it means blood quality can be, and has been checked.) The statement is itself inconsistent with the observation from the stem of the question.
Option B: Economics does not explain why people engage in charity behaviour, e.g. blood donation. Rather, it explains how such behaviour differs under different constraints. People will tend to engage less intensively in blood donation if the cost of doing so is higher or if the return is lower. Assuming a constant preference of charity behaviour (we cannot explain behaviour by preference or taste), in the case of blood donated for free, there is no pecuniary return on donating blood, and the non-pecuniary benefit to blood donors is zero as well if they know their blood is medically dangerous. Therefore, they would tend not to donate their blood.
本年 Paper 2 較有爭議的只有一條，解釋如下：
Paper 2
Q27
The only doubt in this question is whether option (3) is correct. It is NOT correct because PPP is a long-term concept, and it does not imply equalization of prices in terms of a given currency at any point of time. (Arbitrage takes time to restore the PPP condition.)
2009 高考經濟學選擇題答案
* Students may find the data for Q7 and Q8 confusing. Able candidates, however, will notice that no available options are consistent with the assumption of a closed economy and will avail themselves of the figures provided for X and M in the calculation.
** Most candidates would implicitly assume identical horizontal shift of IS curves, therefore choosing C as the answer.
STATEMENT
It is my deepest regret that the MC answers I posted on the web this evening (2 Apr 2009) contains material typographical errors — the correct answers for the two items B and A were mistyped as A and B. I was informed of such error by my assistant only several hours later, and I hereby apologize to you all for the more than obvious errors which I overlooked.
To clarify any misunderstanding the errors may have caused to students, I feel an obligation to explain to all readers who may have been confused by the errors on the two questions.
Q11.
Option A: The law of demand only implies a downward sloping demand curve, saying nothing about the price elasticity, and the “change by a smaller amount” in the option itself has nothing to do with price elasticity without mentioning percentage change. In a word, it’s a totally irrelevant option.
Option B: A higher income tax exemption for children lowers the cost of raising children, implying an increase in birth rate.
Q12:
Option A: Consumer surplus is extracted with two-part pricing, which should be a standard textbook analysis.
Option B: Charging a uniform price would not extract any consumer surplus. In this case, the two groups of people are simply charged two different uniform prices, therefore implying no extraction of consumer surplus.
聲明
是晚 (09年4月2日) 本人於網上發佈的選擇題答案有排版錯誤，其中 B 及 A 答案分別誤排作 A 及 B，對此本人深感抱歉。本人於幾小時後才獲告知此兩項錯誤，在此本人向所有讀者道歉，竟忽略了如此明顯的錯誤。
此錯誤可能讓讀者感到混亂，本人認為有必要在此向各位就該兩條題目作出解釋。
第十一題
A 選項：需求定律只意味着向右下傾斜的需求曲線，對需求彈性並無任何含意；而選項中「需求量的轉變會較小」，在沒有指明百比份的改變的情況下，本身亦與需求彈性無關。簡言之，這是毫不相關的選項。
B 選項：免稅額提高減少養育子女的代價，這意味着較高的出生率。
第十二題
A 選項：兩部定價榨取消費者盈餘，這是標準教科書的分析。
B 選項：收取單一價格不會榨取任何消費者盈餘。這個案只是向兩組人分別收取不同的單一價格，因此並沒有榨取消費者盈餘。
訊息費用與補習市場
訊息費用與補習市場
Where is the knowledge we have lost in information?
- T. S. Eliot
- T. S. Eliot
訊息費用 (information cost) 是高考經濟科的一個重要概念 — 它固然是考核課題之一，且與整個考試的現象相關。若沒有訊息費用，考生各方面的能力眾人皆知，無須考試，也就沒有補習市場了。在訊息費用大於零的情況下，考試有識別學生能力的作用；而與考試有關的訊息費用何其高也，故補習市場應運而生。
按理，同學補習是想減低與考試有關的訊息費用。問題是，與補習市場有關的訊息費用大得驚人。在不完全訊息下 (imperfect information)，賣家隱瞞訊息或發放錯誤訊息有利可圖，司空見慣。補習市場亦不例外，市場充斥着很多錯誤訊息。
有重讀生對我說，「你課堂說的重點我去年補習時完全不知是重點，有些甚至沒有聽過，難怪不及格！」，這是讓人感慨的。考生要從 past papers 中自己參透考試重點，當然不易，否則不用補習了。我奇怪的是，為何考生沒有從 past papers 中發現他補習所學的跟高考所考的南轅北轍？細問之下，原來他的補習名師說，有些 past papers 的題目不重要，不要浪費時間，並已為他們「精」選了重要的，叫他們不用憂心其他題目。又聽聞有些名師說高考經濟科的某部份（該部份佔全卷分數三分之一）全港沒有人能答對，只集中於較淺的其他部份已足以奪A。若跟隨這方法的考生知道該部份全港考生的整體表現和平均分，不知有何感受？有些學生拿某些名師的筆記問我，上面寫的所謂評分參考是否準確，我一看，果然寫得疑幻似真，這樣答兩分，那樣答三分，但考試時寫上這些東西，不遇滑鐵盧才怪。這是補習市場的悲劇。本來應該是減低訊息費用的活動，反倒把訊息費用增至這麼大。
是的，高考經濟科範圍闊，題目有深度，很多名師拿捏不準，編些故事，反正他們不知道的，學生也不易揭穿，而校內的出題和評分標準與公開試往往不一，到放榜之時，明年的主要顧客又是另一批學生了。
問題是，為何事後沒有人更正這些錯誤訊息呢？答案也是訊息費用。在網上留言區所看到的訊息，熟真熟假？有多少是受僱的「打手」以不同IP所編？一般學生基本上不能清楚分辨訊息的真偽。經濟分析告訴我們，已畢業的考生發放訊息的誘因遠低於這些打手。這又是悲劇的另一面。
有些考生本身的能力是高的，但考不到好成績，以為自己資質低劣，作為老師的豈能不替他們感到不值？訊息費用能這樣廣泛地應用於補習市場，是經濟學的悲哀。
Cliff Yeung
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