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A study based on a year-long analysis of data from an extensive mobile phone network has produced interesting information that might be of use to epidemiologists and social scientists. The data, according to the researchers, might shed light, for example, on how diseases and information (or rumours) are transmitted through social networks.
Researchers ranked the link between a pair of phone users on the basis of the total time spent talking to each other. ‘Strong’ links exist between members of a close social group. ‘Weak’ links tend to be more long range and join individuals from different social groups. The researchers observed a dramatically different effect when they removed links in the network in rank order, depending on whether they removed links starting with the strongest or with the weakest. To their surprise, removing the strong links first had little effect on the overall structure of the network. But removing weak links first split the network into a series of unconnected islands, with individual users linked to a small collection of other phone users.
Thus the researchers have hypothesized that the weak links (the more tenuous connections between individuals from different social groups) might be very important in maintaining wider social cohesion. If you lose contact with casual acquaintances you may fragment your social circle, but if you stop talking to your brother there might be a less visible impact on the structure of your social network.