Why your popular friends are more sick than you

Article in The Economist on two interesting properties of social networks that taken together allow early prediction of epidemics.

Firstly, your friends on a social network are more likely to be popular than you:

Consider both an avid cocktail party hostess with hundreds of acquaintances and a grumpy misanthrope, who may have one or two friends. Statistically speaking, the average person is much more likely to know the hostess simply because she has so many more friends. This, in essence, is what is called the “friendship paradox”: the friends of any random individual are likely to be more central to the social web than the individual himself.

Secondly, the interesting property of these popular people is that they are more likely to meet sick people before you do:

By studying the friends of a randomly selected group of individuals, epidemiologists can isolate those people who are more connected to one another and are therefore more likely to catch diseases like the flu early. This could allow health authorities to spot outbreaks weeks in advance of current surveillance methods.

With the result that:

Dr Christakis and Dr Fowler selected a random group of 319 undergraduates and asked each to nominate up to three friends. Using these names, they collected another group of 425 friends. As the friend paradox predicts, the second group were both more popular (named more times by the random group) and more central to the connections among Harvard students. Flu infections were monitored from September 1st 2009 to the end of December by identifying those diagnosed by the university’s health services and by e-mail responses to a twice-weekly health survey. Overall, 8% of the students were formally diagnosed with the flu and 32% were self-diagnosed. But the infection rate peaked two weeks earlier among the group of more-connected friends. Their social links were indeed causing them to get infected sooner......

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As this result came with the benefit of hindsight, the researchers tried to come up with a real-time measure that could potentially provide an early warning sign of an outbreak as it began to spread. To do this they went back to the beginning and compared diagnoses between the two groups on a daily basis for each of the 122 days of the study. A significant difference between the two groups was first detectable a full 46 days before visits to health services peaked for the random group. For those with self-reported symptoms, there was a noticeable difference 83 days before the peak in self-reported symptoms.

So there you have it - next Swine Flu Pandemic, start watching your Twitterfriends with loads of followers with ghoulish iattention.

I may even start following Twitterslebs as a rational of Canary in the Mine strategy

Speaking of people with sick friends more popular than oneself, I hear that BBC Backstage's Ian Forrester (@cubicgarden) is very ill. This post is for him, we wish him a very speedy recovery.