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1、Chapter 5The Buck Starts HereBank RunsNorthern Rock Bank In September of 2007, Northern Rock bank closed its doors for one day and asked the Bank of England to cover its deposits. The brief scare started a chain reaction. Long lines formed outside many branches as people attempted to withdraw their
2、money.Photo by Dominic, FlickrBank RunsWithdrawers knew their actions were unreasonable. Why did so many people show up and stand in line for hours if they thought their money really was safe?Social Networks played a large role. People who had heard that friends were going were more likely to join i
3、n the frenzy. These bank runs are examples of hyperdyadic spread.Millions of pounds were withdrawn causing a financial crisis that effected not only Northern Rock Bank but the entire banking and investing community. Photo by Christopher ElisonPhoto by Lilly, FlickrIndividual rational behavior led to
4、 communally irrational behavior. Bank RunsSocial Networks can make the problem worse.A few panicked people can influence many others, as panic spreads. Photo by Lilly, FlickrTracking the Spread of InformationPhoto by WheresGWhat is the path through a network that things take when they spread? A good
5、 alternative to tracking people is to track the flow of money. WheresG was created to track money. The path of a bill can be traced if enough people input the same bill into the system. Tracking the Spread of InformationApplying the same principle elsewhere can help us understand other types of comm
6、unication within social networks.Researchers study the paths of money, diseases, cell phone calls, emails, and anything else that is traceable.Photos by Ed Yourdon A random walk is a path in which movements are in a random direction and all the steps are equal size. A Lvy Flight is a path in which m
7、ovements are in a random direction but the distance traveled varies with each step. Sometimes, there is a very long step or “flight.”Random Walk and Lvy FlightTracking the Spread of InformationResearchers found that information moving through a network follow a path between a random walk and Lvy Fli
8、ght.Tangible applications include better information about how a disease like SARS might spread.Photo by Christian KeenanMoody Markets These “paths” can affect the way the cost of a good changes. Cost depends on supply and demand. Where does “demand” come from? Social networks, in part.Photo by molo
9、talk and Yoshimai, FlickrSupply:Demand:Moody Markets People set new prices by evaluating what others want.As a result, they are influenced by past prices.This can cause prices to skyrocket (creating bubbles) or to plunge (creating crashes).Photo by runneralan2004, FlickrMoody MarketsHow many jellybe
10、ans? The average of a groups guess can be accurate if they guess simultaneously or without knowledge of others guesses.But when they know about previous guesses, the group does not get as close!Photo by Inkyhack, FlickrIn an efficient market, people decideconcurrently and independently But in social
11、 networks, people decidesequentially and interdependently.The Strength of Weak TiesStrong ties affect people more deeply.Weak ties often link more people.“Bridge” members have many weak ties to members outside their group.Photo by johntrainor, FlickrPeople need both strong and weak ties in order to
12、network successfully.The same is true for companies.Photos by Steve Polyak and Wesley FryerThe Strength of Weak TiesThe Strength of Weak TiesMix of strong ties to previous collaborators and weak ties for fresh faces balances rapport, organization, and creative ability. Broadway shows that follow thi
13、s model are more likely to succeed!Photo by Brian Lane Winfield MoorePower in NumbersWhy not go it alone?Muhammad Yunus earned a Nobel Peace Prize in 2006 for inventing micro-finance banking.Photo by GarmeenBSmall loans were given to groups (usually women) in impoverished countries to start small bu
14、sinesses or projects. Power in NumbersSocial ties, rather than money, were used as collateral and could be used to guarantee a loan.Yunus founded the Grameen Bank which now fosters social networks which optimize trust connect groups through weaker ties help find creative solutions through connectionsPhoto by Inkyhack, Flickr
