It has been frequently mentioned in class that the spread of disease, technology, or ideas may be modeled by social networks. In addition to those aspects, however, it was found by the National Institute of Health (NIH) that the spread of obesity can also be modeled by social networks, such as the social influence of family and friends. In general, “the attitudes, behaviors, and acceptance of obesity also might play an important role.”

The setup of the study was as follows:

The research team gathered data about 5,124 people from the records of the Framingham Heart Study participants. The data consisted of weight, height, and other aspects of the person for up to seven time points from 1971 to 2003. In addition to the Framingham Heart Study participants, they also analyzed information from the participants’ close family members and close friends. Overall, this consisted of a social web of a total of 12.067 people.

Based on the findings, analyst Christakis said, “We didn’t find that people who were overweight simply flocked together. Rather, we found what seemed to be a spread of obesity and that the likelihood of a person becoming obese depended on the nature of the relationship.”

The chance of a participant to become obese was increased by 57% if they had a close friend or family member who also became obese and by 71% if it was a same-sex friendship. The closeness of the tie in the social network is also important, as it was found that if two people acknowledged that they were close friends and one of them became obese, the risk of the other person to become obese was increased by 171%. This was only true if the friendship was openly acknowledged.

Interestingly, it was also found that obesity can spread across social ties even if the geographic distance from one person to another is very large. In fact, the social distance was more important than the geographic distance. For instance, “an immediate neighbor’s becoming obese did not affect a person’s risk of becoming obese.” Also smoking did not correlate with the spread of obesity.

As shown by this study, social networks can affect aspects of human behavior and characteristics of people that are not immediately obvious. Some things that are spread by social networks, such as disease, can be spread just by proximity, while other things, such as obesity, is spread depending on the closeness of ties and the characteristics of other people.

http://www.nih.gov/news/pr/jul2007/nia-25.htm