Transcript prisoners` dilemma

Freakonomics
公民教師研習營
林明仁
國立臺灣大學
經濟學系
Topic 1: game theory
Lets play a game first
• 從1到100的整數中選一個數字（寫下數字
和你的姓名）
• 計算所有人所寫的數字的「平均數」
• 最接近這個「平均數」的「一半」獲勝
Chapter 16: Oligopoly
The Beauty Contest
• A newspaper contest, in which entrants are
asked to choose from a set of six photographs
of women that are the most beautiful. Those
who picked the most popular face are then
eligible for a prize.
Chapter 16: Oligopoly
Chapter 16: Oligopoly
• A naive strategy would be to choose the face that, in
the opinion of the entrant, is the most beautiful.
• A more sophisticated contest entrant, wishing to
maximize the chances of winning a prize, would think
about what the majority perception of beauty is, and
then make a selection based on some inference from
his knowledge of public perceptions.
• This can be carried one step further to take into
account the fact that other entrants would each have
their own opinion of what public perceptions are.
• Thus the strategy can be extended to the next order
and the next and so on, at each level attempting to
predict the eventual outcome of the process based on
the reasoning of other rational agents.
Chapter 16: Oligopoly
• "It is not a case of choosing those [faces] that, to the
best of one's judgment, are really the prettiest, nor
even those that average opinion genuinely thinks the
prettiest. We have reached the third degree where we
devote our intelligences to anticipating what average
opinion expects the average opinion to be. And there
are some, I believe, who practice the fourth, fifth and
higher degrees." (Keynes, General Theory of
Employment Interest and Money, 1936).
• Keynes believed that similar behavior was at work
within the stock market.
Chapter 16: Oligopoly
•
•
•
•
Level 0=50
Level 1=25
Level 2=12.5
Level 3=6.25
Chapter 16: Oligopoly
GAME THEORY AND THE
ECONOMICS OF COOPERATION
• Game theory is the study of how people
behave in strategic situations.
• Strategic decisions are those in which each
person, in deciding what actions to take, must
consider how others might respond to that
action.
19
Chapter 16: Oligopoly
The Prisoners’ Dilemma
• The prisoners’ dilemma (囚犯的困境) is a
very simple game, but provides insight into the
difficulty in maintaining cooperation.
• Often people (firms) fail to cooperate with one
another even when cooperation would make
them better off.
21
Chapter 16: Oligopoly
The Prisoners’ Dilemma
• The prisoners’ dilemma is a particular “game”
between two captured prisoners that illustrates
why cooperation is difficult to maintain even
when it is mutually beneficial.
22
Chapter 16: Oligopoly
Figure 2 The Prisoners’ Dilemma
疼熊 ‘s Decision
Confess
疼熊 gets 8 years
Remain Silent
疼熊 gets 20 years
Confess
是蚊gets 8 years
是蚊’s
Decision
疼熊 goes free
是蚊goes free
疼熊
Remain
Silent
是蚊gets 20 years
23
是蚊gets 1 year
gets 1 year
What happen if you play prisoner’s
dilemma in really life?
• https://www.youtube.com/watch?v=p3Uos2fzIJ0
• Golden Ball
•
Steal Split
• Steal (0 , 0) (100,0)
• Split
Chapter 16: Oligopoly
(0,100) (50,50)
The Equilibrium for an Oligopoly
• A Nash equilibrium is a situation in which
economic actors interacting with one another
each choose their best strategy given the
strategies that all the others have chosen.
• (Confess, Confess) is a NE if, given that B
confesses, A’s best strategy is to confess, and
vise versa.
25
Chapter 16: Oligopoly
Oligopolies as a Prisoners’ Dilemma
• Self-interest makes it difficult for the oligopoly to
maintain a cooperative outcome with low production,
high prices, and monopoly profits.
• But some time they stick on for sometime, like OPEC
• Real world Law Example:
• 友達vs 三星
• Collude for a while,
• US department of Justice: violate Anti-Trust law
• DA played prisoner’s dilemma game.
• Whistle Blower!
27
Chapter 16: Oligopoly
Real world Legal example: Belgium
• Belgium: few traffic signs, when approaching
intersections, he who “stops and looks” lose the
right to proceed first! So 路口加速: send a signal
to other driver that he is dangerous, and any sign
of hesitation often spurs other drivers to hit the
gas!
• To slow down is to show weakness!
• Belgium: 11.2 death per 100,000, and 2/3 of
them is fail to yield. Nearby countries: 4-8
• How to solve this? A law that changes the payoff!
Stop sign!
Chapter 16: Oligopoly
Topic 2 Economics is everywhere!
Let’s do some tests first
根據《超爆蘋果橘子經濟學》，以下何者最有助於改善印度農村婦女的生活？
(1)印度政府禁止夫家索取嫁妝和視性別選擇墮胎(2)有線電視和衛星電視的普及 (3)
付錢鼓勵婦女不要墮掉女胎 (4)專門針對印度市場設計製造的保險套
下列哪一個不是WEGO motel 折價卷上印的折價時段?
(1)下午1點到5點(2)晚上5點到7點(3)早上7點到12點(4)星期日
下列哪一個原因對台灣這幾年生育率下降影響最大?
(1)景氣不好(2)養一個孩子太貴(3)年輕人一直玩一直玩不想生(4)高等教育擴張
大學低學費可以讓窮人家的小孩有翻身的機會，促進階級流動與社會公平正義
•
Another example for price
discrimination
怪咖如何把經濟學界搞的天翻地覆？
The legend of Steve Levitt
• Traditional Economics is about
consumption, interest rate, or GDP,
• Image of traditional economist: boring,
speak Mars Language (aka math).
• Example:
• http://blogs.wsj.com/digits/2009/05/20/t
-mobile-brings-catherine-zeta-jonesback/tab/article/
In fact, freakonomics has started already
 Beauty matters? Why?
 Beauty is Symmetry, (Whoops, it is skin deep)
 But it is deeper: Beautiful people are healthier
(so it is not skin deep)
 So cosmetic surgery is actually messing up with
nature’s selection process.
 How big is the effect?
 In wage (Hammermash), election(駱明慶),or
even teaching evaluation!
Then here comes Steve ! And all is Bright!
(芝大經濟系教授,
(#2 seller at Amazon)
2004 Clark Medal)
In Freakonomics, we saw
• Abortion reduces Crime
• Teachers, Sumo Wrestlers, and Real Estate
Agents
• are all Cheaters.
• Drug dealers still live with their mom.
Gang leader for a day: Venkedesh
Can Economics
explain everything?
Yes we (almost) can!
Our ultimate weapon: incentive-something that induces a person to act,
i.e. the prospect of a reward or
punishment. Rational people respond to
incentives because they make decisions
by comparing costs and benefits
Ex: higher gas prices, higher sales of
“hybrid” cars. Higher cigarette taxes,
teen smoking falls.
為什麼一顆腎要等30年?
•
•
•
•
•
沒有誘因
善心捐贈 P=0
Excess demand
Iran
流浪教師也一樣
Steve Levitt
(芝大經濟系教授,
(#2 seller at Amazon)
2004 Clark Medal)
Chapter 16: Oligopoly
Discrimination against Women
• Ex: India: ”May you be the mother of hundred
sons”, ”500 Rubis now, save 50,000 Rubis later”
• Even for Harvard graduates:
• 有工作的女生比男生薪水少30% (Katz &
Gordan,
• What is the best way to improve women’s
status?
• 教育?
• 政令宣導?
• 叫男人要愛老婆?
• At least in India….
Watch Plywood soap opera!
Oster and Jenson(2010) QJE
• Introduction of cable television is associated
with signicant decreases in
• (1)the reported acceptability of domestic
violence towards women (2) son preference,
(3) increases in women's autonomy and
decreases in fertility.
(C) Prostitutes
• P & Q are determined by Demand and Supply !
• 建築師(or 大學教授) 與sex worker 的薪水比
較? Supply and demand
• Superfreakonomics provides three ways to
look at the this topic: historical data, current
days survey, and 深度訪談。
• 當性工作者的成本: 羞恥心，風險較高， 無
法轉行當太太。
Historical data: Chicago in 1910
 Report from the vice commission:
女性類別
週薪（當時價格） 年薪（現在價格）
女店員
6 美元
6500美元
低價妓女
（可能是阻街）
25美元
25000美元
妓院賣身的妓女
70美元
76000美元
Everleigh Club
400美元
430000美元
 Everleigh sisters 退休時， 存了約現金幣值2200
萬美金!
Everleigh Club: 當年高級招待所
• 顧客包含：商業鉅子，政治人物，運動員，
藝人，以及反賣淫人士!
• 老闆 Everleigh 姊妹對員工 提供健康飲食，
醫療照護，才藝教育。
• 小姐們迷人，注重衛生，值得信賴， 也能
與客人騷文弄詩，引經據典。
• 入場費250美元，香檳一瓶370美元， 服務
1250美元。
Current Data: Chicago Street
 Venkatesh(凡卡德希)與李維特收集芝加哥南邊
160名妓女的2200次交易紀錄，包括:細節和時
間長短，地點，金額，毒品，顧客，種族，年
齡，帥否，保險套，已婚…..
 發現:
 (1)每周工作13小時，接客10次，時薪27美元，
周薪350美元(包含向顧客偷的錢)。
 (2)83% 的妓女有毒癮(接受毒品支付酬勞) 。
 (3) 妓女們通常有多份工作(理髮，偷竊， 把
風…)，但80%所得來自賣淫。
• (4)平均一年12次被顧客施暴 (主因為不
能勃起)，160個樣本中 一年內有3人喪
命。
• (5)價格與銷售量
服務項目 打手槍
口交
陰道性交 肛交
價格
$26.7
$37.6
$80.05
$94.13
市占率
15%
55%
17%
9%
• (6)對白人差別取價。
其他(純
聊天,
group…)
4%
• (7)折扣: 毒品支付(-$7)，戶外(-$6.5)，使用保
險套(-$2, 這和墨西哥的資料不同)。
• (8)相同地點，不同妓女(不論條件好壞)，索
價相同 ---完全替代perfect substitute.
• (9)皮條客效用
妓女
每周平均交易次
數
周薪
自行接客
7.8
$325
和皮條客合作
6.2
$410
• (10)警察的角色(代理人問題: 仲介，水果攤…)
• (11)國慶日加班: 需求大漲，兼差的人也增加。
Case Study: Ally in Chicago
• 一開始$300/hr，每周工作30小時後來每周
工作15小時，價格一路調高到$500 美元--反而更搶手!年收入超過20萬。
• Price –insensitive
• 而且工作內容也有很大的改變: 每天有好幾
個”一小時” 約會，和只有兩個三小時的約
會，內容完全不同。
• 這跟咖啡在星巴克賣和在SEVEN賣家差很大
一樣 bundling…
為什麼百年前的妓女賺得多?
女性類別
週薪（當時 週薪（現在
價格）
價格）
年薪（現在價格）
百年前女店員
6 美元
138 美元
6500美元
百年前低價妓女
25美元
575美元
25000美元
百年前妓院賣身的妓女
70美元
1610美元
76000美元
百年前Everleigh Club
400美元
9200美元
430000美元
現代女店員
300美元
15000美元
現代芝加哥低階妓女
350美元
18000美元
現代愛莉
200000美元
這跟現在勞工的處境沒什麼兩樣: substitutes decrease your wage!
Need to increase your added value! Learn new tricks!
Topic 3: Long Run Economic Growth
Note: (1) 縱軸取log, so slope is the growth rate. (2) the whole world’s GDP
per capita hardly grew between 1500 to 1800 (population and “total” GDP
grew, though) (3) look at all the critical break points….
Chapter 16: Oligopoly
現代經濟成長的定義
• 19世紀初以前,世界各國都是傳統農業經濟:
所得低,而且平均每人GDP成長率甚低,幾
乎等於零。
• 現代經濟成長(modern economic growth):
• Kuznet: 一個社會脫離傳統農業經濟, 平均
每人GDP成長率持續大於零, 平均每人GDP
水準逐年上升的現象。
經濟發展 Economic Development
• promote the standard of living and economic health of
a specific area.
• including development of human capital, critical
infrastructure, environmental sustainability, social
inclusion, health, safety, literacy, and other initiatives.
• Economic development differs from economic growth.
• One aims for economic and social well-being of people,
• the other, GDP only.
• Amartya Sen points out: “economic growth is one
aspect of the process of economic development.
• UN: Human Development Index
Table 3 GDP and the Quality of Life
Wealth makes you happy?
Chapter 20: Income Inequality
and Poverty
• Hans Rosling's 200 Countries, 200 Years, 4
Minutes - The Joy of Stats - BBC Four
從居住環境的變化看台灣長期經濟成長
• Taiwan’s GDP per capita (US$ 1990 ) 1820: 550, 1900: 560, 2003:17,824.
• 100年來到底有多大變化？
• 皇后飯店(Queen’s hotel)的故事:
•
•
•
•
•
•
1872, 馬偕與英國的BAX投宿於中壢的皇后飯店，馬偕說：「和一般漢人旅館
比較這一家是較乾淨的。 但是豬群和雞鴨在室內走動，房間充滿惡臭，床上
只有一張骯髒的草席。」
1875,英國的 M.Beazeley 至台灣南部尋找建造鵝鑾鼻燈塔之地點， 6月20日
抵車城， 清朝官員周有基特地讓出自己的房間…
但 Beazeley 發現：「房間窄小悶熱，臭氣沖天。臭氣來自一個露天的、穿
過房間地表的排水溝。」
Beazeley 於是打算在後院搭帳蓬，卻發現「後院是骯髒的泥濘地，散滿各種
污物，豬群在地上翻滾。」
日治初期的台北市呢？「房舍中流出污水，到處有沼澤，或是人與狗豬雜居。
雖然到處有公共廁所，但都積滿了糞便。」
台灣的經濟成長，從1900年開始…wait till the chapter of economic growth.
台灣的現代經濟成長之一：日本時代
• 台灣的現代經濟成長出現於日治初期。學
者估計,
• 1910–42之間, ΔA/A = 2.048%。1920前：
肥料推廣與水利衛生建設。 1920後： 新
品種與耕種技術進步。
• 法律與治安(law and order)
• 保障財產權-1898 臨時台灣土地調查
• 基礎建設-縱貫鐵路、水道
• 強化市場制度
台灣的現代經濟成長之二 1960-2005
• 亞洲四小龍:台灣,香港,南韓,與新加坡
• 1960年,台灣平均每人GDP之排名為第65
(n=106), 2005年,全世界排名第28
(n=148), why?
• 持續的infrastructure
• Human capital
• Industrial policy?
Institution Effect and Why Nations Fail
Chapter 16: Oligopoly
Chapter 16: Oligopoly
Key finding: “Protection against Expropriation(徵收) Risk” and GDP are
positively correlated
Expropriation: a public agency takes private
property for a purpose of “public” interest".
Restat 2009
They argued it is the legal system( and a more stable or better structured government),
and only ready for transfer after 1700
The book itself
• Inclusive(廣納) vs Extractive(搾取)
• Chap 1: so close yet so different: post a
puzzle…
• Chap 2: theories that don’t work: 打臉章
• Geography Hypothesis: Diamond
• The Ignorance theory?
• Cultural hypothesis: still use regression
discountinuity: Congo river, US Mexico border
Topic 4: Some questions you raised
Principle #2: The Cost of Something Is What
You Give Up to Get It
• Making decisions requires comparing the
costs and benefits of alternative choices.
• The opportunity cost of any item is the
highest value of whatever must be given up to
obtain it. (放棄的東西中,最有價值的那一個)
• It is the relevant cost for decision making.
CHAPTER 1 TEN PRINCIPLES OF
ECONOMICS
HOW PEOPLE MAKE DECISIONS
Examples:
The opportunity cost of…
…going to college for a year is not just the tuition,
books, and fees, but also the foregone wages.
…seeing a movie is not just the price of the ticket, but
the value of the time you spend in the theater.
…coming to my class for three hours….
CHAPTER 1 TEN PRINCIPLES OF
ECONOMICS
Example 1
• 野田妹大學畢業了，正在考慮是否要出國唸音樂學
院，如果決定出國，她必須要負擔學費USD30,000
／年、食宿多出USD10,000／年、其他開銷多出
USD12,000／年，但是一年後每年可以有
USD100,000的收入；如果不出國，野田妹可以當幼
稚園音樂老師，一年收入約USD20,000，也可以從
事音樂表演，一年收入約USD50,000。請問：野田
妹出國唸音樂學院一年的機會成本是多少？
• ANS: USD102,000 （4分）
• 放棄了30000+10000+12000+50000
• 那如果是從事音樂表演的機會成本是多少？
• 明年開始， 每年多出來的五萬元 discount 回來
CHAPTER 1 TEN PRINCIPLES OF
ECONOMICS
Example 2
• 你得到一張免費阿蜜特演唱會門票（不能
轉售） 。
• 菜一鄰演唱會在同一天晚上， 是你的次佳
選擇， 門票40元。 你最多願意付50元去聽
對菜一鄰的演唱會。
• 去聽阿蜜特的演唱會， 你的機會成本是多
少？
• (A)$0 (B)$10 (C)$40 (D)$50
CHAPTER 1 TEN PRINCIPLES OF
ECONOMICS
• the most popular answer at AEA for Econ Ph.D
students was $50(27.6%), the second most
popular answer was $40(25.6%).The third
most popular answer was $0 (25.1%).
• The correct answer was $10.
• 為了去阿蜜特，你損失了本來可以拿到去
菜一鄰的$50 好處， 但也避免付出40塊成
本 (An avoided benefit is a cost, and an
avoided cost is a benefit) 。 所以為了看阿蜜
特你放棄了去看菜一鄰可以得到的net 10元
好處（net profit）。
CHAPTER 1 TEN PRINCIPLES OF
ECONOMICS
• 小明剛從大學畢業，正準備投入職場就業，下表是A、B、
C三家公司所提供的薪資待遇，以及小明選擇A、B、C三家
公司每個月所須付出的交通費。假設這三家公司的工作內
容相同，請問：在不考量時間成本的情況下，小明選擇A、
B、C三家公司的機會成本何者最低？
A
B
C
薪水
30000
25000
28000
交通費
5000
0
2000
Net benefit
25000
25000
26000
• 隱藏成本應該是所有其他公司的薪資減去
交通費得到的淨值(net benefit, cause this is
what you give up)中價值最高者，加上該公
司的交通費(外顯成本)，得到機會成本
Net benefit
(profit)
25000
25000
26000
A
B
C
外顯(交通費)
5000
0
2000
隱藏
26000
26000
25000
Total opportunity 31000
cost
26000
27000
But you get(ie 薪
水)
25000
28000
30000
甲方案：興建
1,000億元
0
維修成本
ru83
乙方案：不興建
300億元
500億元
經濟效益
1,200億元
0
觀光效益
150億元
700億元
建設+維修成本
經濟＋觀光效益
甲方案：興建
1,300億元 (A)
1,350億元(B)
乙方案：不興建
500億元(C)
700億元(D)
explicit cost
1300(A)
500(C)
Implicit cost
200(D-C)
50(B-A)
Total cost
1500(A+D-C)
550(C+B-A)
Benefit
1350(B)
700(D)
建設成本
選乙方案: 賺到700, 放棄了550 (建設成本500, 跟選甲得到的的 net
beneift=50)
(所有的數字都要進去, 而且只能進去一次, 不然就double counting)
若選乙 一定是B-A-D+C<D-C-B+A,移項得2(D-C-B+A)>0
D-C>B-A 跟直接比net profit 一樣
From Autarky to free trade: the price will
adjust to the point that excess demand in
UK=excess supply in Japan(Warlas Law )
出口供給線（export supply curve ）
就是在不同價格下的超額供給