"Friendship Paradox” Helps Predict Spread of Influenza

A new study claims that the "Friendship Paradox,” which states that statistically, the friends of any given individual are likely more popular than the individual herself, could help predict the spread of infectious disease.

Researchers at Harvard University (Boston, MA, USA) and the University of California San Diego (UCSD, USA) used the paradox to study the 2009 flu epidemic among 744 students, composed of 319 Harvard undergraduates, who in turn named a total of 425 friends. Monitoring the two groups both through self-reporting and data from Harvard University health services, the researchers found that, on average, the progression of the epidemic in the friend group occurred 13.9 days in advance of the population as a whole. The friend group also showed a significant lead-time on day 16 of the epidemic--a full 46 days before the peak in daily incidence in the population as a whole. The study was published on September 15, 2010, in the journal PLoS ONE.

"By simply asking members of the random group to name friends, and then tracking and comparing both groups, we can predict epidemics before they strike the population at large. This would allow an earlier, more vigorous, and more effective response,” said coauthor Nicholas Christakis, M.D., Ph.D., a professor of medicine, medical sociology, and sociology at Harvard.

"This study may be unique in demonstrating that social position affects one's risk of acquiring disease. Consequently, epidemiologists and social scientists are modeling networks to evaluate novel disease surveillance and infection control strategies,” said John Glasser, Ph.D., M.P.H., a mathematical epidemiologist at the U.S. Centers for Disease Control (CDC; Atlanta, GA, USA). "The study should cause infectious disease epidemiologists and public health practitioners alike to consider the social contexts within which pathogens are transmitted.”

To comprehend the friendship paradox, take a random group of people, ask each of them to name one friend; on average, the named friends will rank higher in the social web than the ones who named them, since the friends named will weigh heavily in the direction of the well-connected host; few people will name a recluse. Moreover, since the people at the center of a social network will come across gossip, trends, and ideas sooner, they are also exposed to diseases earlier than those at the margins of the social network are.

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Harvard University
University of California San Diego