In 1967, the American social psychologist Stanley Milgram sent out 160 packages to randomly chosen individuals in the U.S., asking them to forward them to a single individual living in Boston. The task included a simple rule: The recipients could only send each parcel on to somebody they knew on a first-name basis.
To his surprise, Milgram found that the first package arrived at its
destination via only two people. On average, he found that the parcels reached
their destination via five pairs of hands, which amounts to 6 degrees of
Milgram’s work has since been repeated on various social networks. For
example, Microsoft says people on its Messenger network are separated by 6.6
degrees of freedom and Facebook claims its members are separated by only 4
degrees of separation.
But there is another element to this work that has been less closely
studied, which is the time it takes to travel across a network. In Milgram’s
experiment, the first package arrived in just four days. But the others took
So an interesting question is how quickly is it possible to traverse a
social network — to track down a random individual across the network.
Today, we have an answer thanks to the work of Alex Rutherford at the
Masdar Institute of Science and Technology in Abu Dhabi and a few pals who have measured
how quickly it is possible to track down random individuals around the world
using social networks.
They concluded that, on average, any individual is just 12 hours of
separation from another.
Their data comes from a competition called the Tag Challenge, in which the
goal was to find five individuals in five different cities in North America and
Europe. The only clue was a mugshot of the
individual, the name of the city he or she was in and the fact that they would
be wearing a T-shirt with the logo of the event.
Rutherford and his team won the competition by identifying three of the
five individuals in just 12 hours.
They say a key factor to achieving this feat was the ability of
participants to target other individuals who may be to help. That’s in contrast
to another strategy which is blindly gathering as many different people to help
“We have shown that this 12 hours of separation phenomenon relies crucially
on the ability of social networks to mobilize in a targeted manner, using
geographical information in recruiting participants,” they say.
Their data shows that one in three messages were targeted in an appropriate
way during the most time sensitive part of the task. This indicates that social
networks are able to tune their geographical communication to suit the task in
And Rutherford and co say but it may be possible to get participants to
react even more quickly using appropriate incentives.
That’s an interesting observation that may have important applications for
the way politicians and grass roots organisations mobilise support. It may also
help in emergency situations such as in tracking down individuals.
However, Rutherford and co-fail to address
the important question of false positives, when individuals who are not
legitimate targets are falsely identified.
That’s unlikely when the target is wearing a T-shirt with the competition
logo on it. But the recent social media frenzy over the Boston marathon bombings, and the erroneous
finger-pointing that occurred on social networking sites such as Reddit, shows
that this is an important factor.
Perhaps future work can throw more light on how false positives can be
handled and avoided.
But given the significant impact that these kinds of mistakes can have on
individuals, important questions remain over whether social media will ever be
a suitable medium for tracking individuals in this kind of situation.
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