In 1973, the sociologist Mark Granovetter published a paper called “The strength of weak ties” in which he put forward the idea that information largely spreads through society between individuals with weak connections rather than strong ties.

His evidence came from asking a few hundred people how they found their jobs. It turned out that the most common route was through vague acquaintances  rather than through strong friends.   Since then, Granovetter’s paper has become one of the most highly cited and influential in the field of social network theory. 

But what of the role of strong ties? Today, Marton Karsai and pals at Northeastern University in Boston show that strong ties can actually hinder the spread of information through a network.

These guys looked at over 600 million time-stamped  mobile phone calls between 6 million people over six months in an unnamed European country. The analysis of these kinds of datasets has become common in recent years but Karsai and co have a new trick up their sleeves.

While most work in the past has looked at the connections between individuals averaged over time, Karsai and co looked in detail at the way an individual’s connections–that person’s egonet–evolved over time. That’s important because it can reveal important characteristics about social interactions that would otherwise be lost. “The concurrency, and time ordering of interactions, even if the social network contains stable relationships, are crucial and may have considerable effects,” they say.

Having characterised the way egonets evolve, they then simulated this behaviour by creating a network of artificial agents that make connections with each other in the same way. Finally, they examined the way rumours spread through such a network to study  the role that  strong and weak ties  play as the network changes over time. 

The results are somewhat counterintuitive. It’s easy to imagine that rumours arrive via people you have the strongest ties with. But Karsai and co say this does not appear to be true. Instead, strong ties tend to hinder the spread of rumours because they confine information to a group that largely communicates with each other.

So not only do weak ties promote the spread of rumours, strong ties tend to hinder it. 

What’s interesting about this result is that it only emerges when the time-varying nature of the network becomes visible. “The presented results underline the subtleties inherent to the analysis of dynamical processes in time-varying networks,” say Karsai and co. 

So it’ll be fascinating to see what other insights emerge from this kind of work.

Ref: arxiv.org/abs/1303.5966: The Emergence And Role Of Strong Ties In Time-Varying Communication Networks