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May 16, 2011

How 20% of Social Network Actions or Actors Determine 80% of Results

By Gary Kim, Contributing Editor
If you wanted to nudge people on a social network into trying a new product or get a biochemical system to turn compound A into compound B, you could just push your product or compound into every entry point in the network. But that’s sort of a silly approach, says Jean-Jacques Slotine of MIT (News - Alert). A much more efficient tactic would be to target just the nodes needed to get the desired outcome.



So, along with colleagues Albert-László Barabási and Yang-Yu Liu of Northeastern University in Boston, Slotine developed an algorithm that calculates the minimum number of these driver nodes and finds them. "Dense networks, on the other hand, such as many social networks, were much easier to control: Influence roughly 20 percent of the nodes and the whole network responds.

The number of nodes needed to control a whole network mostly depends on the average number of connections per node, the researchers found. Sparse networks, such as the regulatory system controlling genes in a yeast cell, are pretty resistant to control; roughly 80 percent of the nodes need to be influenced to get the desired outcome. 

Dense networks, on the other hand, such as many social networks, were much easier to control: Influence roughly 20 percent of the nodes and the whole network responds. That’s the sort of think marketers find irresistible. 

“I found that very shocking,” says Magnus Egerstedt, director of the Georgia Robotics and Intelligent Systems Laboratory at Georgia Tech. “Social networks, which seem to be these random, ad hoc collections of people freely expressing information and sharing their thoughts, those were much easier to control than other networks.”

The researchers worked to create an algorithm that quickly tells you both how many points need to be controlled, and where those points -- known as "driver nodes" -- are located.

Next, the researchers figured out what determines the number of driver nodes, which is unique to each network. They found that the number depends on a property called "degree distribution," which describes the number of connections per node.

“Most large complex networks have been created for some practical purpose: metabolic networks to process the food we eat, the Internet to transfer information, organizational networks to achieve the goals of an organization,” said Barabási.  

For the 800 million nodes of the World Wide Web in 1999, the typical shortest path between two randomly selected pages is thus around 19, assuming that such a path exists, which is not always guaranteed because of the Web’s directed nature.

The research will undoubtedly prove useful for marketers at some point, as the researchers suggest large, complex systems are not chaotic, but essentially structured, despite the lack of central coordination. In principle, the research suggests marketers can, in fact, reach 20 percent of Internet users and influence the remaining 80 percent. Marketers love that sort of thing.
Gary Kim (News - Alert) is a contributing editor for TMCnet. To read more of Gary’s articles, please visit his columnist page.

Edited by Rich Steeves
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