Hong Qi
Strong and Weak Ties
 In the late 1960s, Mark Granovetter interviewed
dozens of managerial and professional workers, asking
them who helped them find their current job. Was it a
friend?
 He kept getting the same reply: No, it was not a friend.
It was just an acquaintance.
 Today Granovetter’s paper, The Strength of Weak Ties,
is recognized as one of the most influential sociology
papers ever written.
Strong and Weak Ties
 In The Strength of Weak Ties Granovetter
proposed something that sounds preposterous
at first:
When it comes to finding a job, getting news,
launching a restaurant, or spreading the latest
fad, our weak social ties are more important
than our cherished strong friendships.
Strong and Weak Ties
 In Mark Granovetter’s social world, society is
structured into highly connected clusters, or close-knit
circles of friends, in which everybody knows everybody
else.
 Strong ties are your family, friends and other people
you have strong bonds to.
 Weak ties are relationships that transcend local
relationship boundaries both socially and
geographically.
 Weak ties are more useful than strong ties
Strong and Weak Ties
Weak ties play a crucial role in our ability to
communicate with the outside world. To get new
information, we have to activate our weak ties.
Erdős Number
Number of links
required to connect
scholars to Erdős, via
co-authorship of papers
Erdős wrote 1500+
papers with 507 coauthors.
Erdős Number
 Erdos has Erdos number zero. Those who coauthored a
paper with him have Erdos number one. Those who
wrote a paper with an Erdos coauthor have Erdos
number two, and so on.
 The very existence of the Erdos number demonstrates
that the scientists are linked to each other through the
papers they written.
Erdős Number
 The smallness of most Erdos number indicated that
this web of science truly is a small world.
 As it only rarely happens that the authors of a
publication do not personally know each other,
coauthorships represent strong social link.
Clustering Coefficient
 Watts and Strogatz introduced a quantity called the
clustering coefficient.
 The clustering coefficient tells you how closely knit
your circle of friends is. A number close to 1.0 means
that all your friends are good friends with each other.
On the other hand, if the clustering coefficient is zero,
then you are the only person who holds your friends
together, as they do not seem to enjoy each other’s
company.
Clustering Coefficient
 Clustering measures the fraction of neighbors of a node
that are connected themselves
 Regular Graphs have a high clustering coefficient
 but also a high diameter
 Random Graphs have a low clustering coefficient
 but a low diameter
 Both models do match the properties expected from real
networks!
Clustering Coefficient
 The surprising finding of Watts and Strogatz is
that even a few extra links are sufficient to
drastically decrease the average separation
between the nodes. These few links will not
significantly change the clustering coefficient.
Hubs and connectors
Goriola Dawodu
Hubs and connectors: are the
ubiquitous, a building block of
our complex, interconnected
world.
Malcom Gladwell’s (staff writer at New
Yorker magazine) test:
measures how social you are
 Gives a list of 248 surnames complied from Manhattan
phone book and ask you to give yourself a point if you
know anybody with that name, if you know 3 people with
the same surname on the list, you earn 3 point
 The list was run in a college in Manhattan : an average score
of 21 was recorded
 A group of highly educated academics scored 39
 In college class, the score ranged from 2 -99,in a random
sample, the low score was 9 and the high score was 118
 For highly homogenous group of people with similar age,
education and income the range was enormous. The lowest
score was 16 while the highest score was 108
Conclusion:
 “sprinkled among every walk of like……
are a handful of people with a truly
extraordinary knack of making friend
and quaintances. They are connectors.”
Fact about connectors
 Fundamental properties of most network
 Nodes with anomalously large numbers of links
 Present within the economy and within cells
 Important component of social network
 Create trends and fashion
 Make important deals, spread fads , or help launch a
restaurant
Cyberspace
 An ultimate forum for democracy where everybody’s
voice can be heard with equal opportunity.
 Content are hard to censor , once they are posted they
are instantaneously available to hundreds of millions
of people around the world with internet connection
 The more incoming link pointing to your webpage ,the
more visible it is
 Just as in a society, a few connectors know an usually
large number of people---- large architects of the
World Wide Web (www) is dominated by a few very
highly connected nodes or hubs
 Cyber Hub includes ------Amazon, yahoo, hotmail etc
 Hubs are website to which everyone links
 Hubs are the strongest argument against utopian
vision of an egalitarian cyberspace
 These hubs are visible everywhere and also other link
point to them
 In the network behind the web many
unpopular or seldom noticed nodes with
only a small number of links are held
together by these few highly connected sites
 Student from colleges saw Kevin Bacon’s movie on air,
they tried to prove that Bacon is a God by proving to
the audience that Bacon had played in so many movie
that could connect him to just about any actor in
Hollywood
 The proof showed that Bacon is no closer to the center
of Hollywood than to the center of the universe
 It was observed that every actor in Hollywood could be
connected to Bacon with typically two to three links.
 Two computer science students realized that
determining the distance between two actors is viable
computer science project. ---The two students did not
watch the Bacon movie
 They created an oracle database (www.imdb.com)
 On the website, if you type in the name of two actors
in milliseconds it provided the shortest path between
them, listing the chains of actors and movies through
which they are connected
 This was possible because Hollywood forma densely
interconnected network in which nodes are actors
linked by movies in which they have appeared
Observation
 An actor has link to all other actors
 Those who have played in several movies linked quickly
 Each actors have an average of 27 links ,many more than





the necessary one to make the network fully connected
Each actors can be connected to another actor through
three links on average
Six degree is unavoidable
41 percent of the actors have fewer than ten links
Removing a few actors reduced the length of path to other
actors
The more movies an actor plays the shorter his or her
average distance to his or her peer
 It was found that actors with more movies failed





to give the most connected actors
This indicates that when it comes to network the
size does not always matter.
Despite the number of movies porn stars make,
they fail to be anywhere near the center of
Hollywood
Also, Bacon was a prominent Hollywood actor
who has played over forty-six movie, collecting
link to more than 1,800 actors. His average
separation from everyone else in Hollywood was
2.79
The actor (Rod steiger) with the closest separation
had a separation of 2.53
Bacon was not only far from the universe but also
far from Hollywood
Conclusion:
 As networks are clustered, nodes that
are linked only to nodes in their cluster
could have a central role in that
subculture or genre
Random universe
 A random universe does not support connectors. If the
society were random, then the Gladwell modest social
sample of 400 people, with their average of around 39
social link, the most social person should have a far
fewer acquaintances than 118 found.
 If the web were a random network, the probability of
there being a page with five hundred incoming link
will be practically zero (i.e. Hubs are forbidden in
randomly linked web).
 The average separation between two randomly
selected people on the earth is six
 The distance between anybody and a connector is
often only 1 or t2
 Two pages on the web are 19 clicks away
 Yahoo.com, a giant hub, is reachable from most
WebPages in 2 or 3 click
 The Hub makes the world indeed tiny