Jure Leskovec
Stanford University
The Web is my
Large on-line
“laboratory”
for
applications with
understanding
hundreds of the
millions
of users
pulse
of humanity.
3
Model as an interaction network
4
Collect 40 million articles, posts / day
Study media ecosystem at large
2008 U.S. presidential election campaign
Blogs trail mass media for 2.5h on average
(but professional blogs lead!)
8
Newspapers
Pro Blogs
TV
News Agencies
Blogs
Entertainment
Blogs
Mainstream media
10
Blogs
Mainstream media
Predicting new links on Facebook
Out of 20k we select 20 and get 8 right!
–
+
?
+
+
+
+
–
–
–
–
–
> 90% accuracy
Observations:
Big data
Actively
influencing
the system
Models:
Predictions
Algorithms:
Applications
14
How to change
human
Observations:
Data analysis
behaviors..
Actively
influencing
the system
Models:
Predictions
Algorithms:
Applications
… to evolve into a
“happy” network?
15
16
Predicting links on
We get ~50%
Observations:
ofData
them
right
analysis
But, what is global utility?
Actively
influencing
the system
vs.
Models:
Predictions
Algorithms:
Too “cluttered”
evolveApplications
into a
How to
“happy” network?
Too sparse
20
 Why are networks organized the
way they are?
 Build models/understanding
 Make predictions
 Large data
 Observe/model patterns not
visible at smaller scales
 Three axioms of Physchohistory:
 Detailed data about the population
 Population should be sufficiently large
 The population should remain in
ignorance of the results
Can we do it today?

combines history, sociology,
and mathematical statistics to
make (nearly) exact predictions
of the collective actions of very
large groups of people, such as
the Galactic Empire.

What’s next?
 psychohistorians, masters of an
esoteric mathematical science
that enables them to plan for the
future of their galactic civilization
and realize their plans by making
minimal changes in the society
around them

Psychohistory depends on the idea that, while one cannot
foresee the actions of a particular individual, the laws of
statistics as applied to large groups of people could predict
the general flow of future events.

Asimov used the analogy of a gas: an observer has great
difficulty in predicting the motion of a single molecule in a
gas, but can predict the mass action of the gas to a high
level of accuracy

If we’d want to predict future we would need:
 The population whose behavior is modeled should be
sufficiently large
 The population should remain in ignorance of the results