“Obesity runs in families - and friends, too”, by Alvin Powell of the Harvard News Office, can be found here:

http://www.news.harvard.edu/gazette/2007/03.08/09-obesity.html

            This article summarizes some of the conclusions made from the Framingham Heart study by Nicholas Christakis, professor of medical sociology at Harvard Medical School and professor of sociology in the Faculty of Arts and Sciences. The Study collected information about health, diet, and exercise, along with information about the family and friends of each of the subjects of the study. Taking periodic measurements every two to four years beginning from 1948, the Study was able to cover the spread of three generations: grandparents, parents, and children.

            Data from the Study show that Americans are indeed gaining weight: “The percentage of adults aged 20 to 74 who are overweight has increased from 44.8 percent in 1960 to 65.2 percent in 2002. Those who are seriously overweight or obese increased from 13.3 percent to 30.5 percent over the same period.” Christakis, after studying the case of 5,124 children and their families and friends, was able to determine a correlation between mutual friendship and weight gain. He noticed the most significant chance of weight gain occurred when two people each considered the other a friend. If a friendship were directed in only one way, the weight gain of a person named as a friend was often not affected by the weight gain of the person doing the naming. Thus the directionality of the friendship-weight gain connection is concluded to be two-way.

            Christakis also found that gender also affected weight gain between friends. In his words, “Men are much more influenced by weight gain in men and women influenced by weight gain in women.” This is an important distinction to make. Gender introduces an additional commonality between members of the study, thus creating a kind of focal point as described by Kossinets and Watts. As discussed in their analysis, students who shared a class were more likely to exchange email. This situation can be transferred to weight gain in that people of the same gender were more likely to affect each other’s weight gain.

            By determining the correlation between friendship and weight gain, the directionality of such friendships, and the focal point around which most weight gain is associated, Christakis managed to draw a few conclusions about the network effects of obesity. While these trends were too complicated to be described exactly (“more akin to the ripples and interference patterns generated by throwing a handful of stones into a still pond than that of dropping in a single rock”), he did notice a change in accepted societal norms of weight. He believes that such data of weight gain can be explained in part by “the acceptability of gaining weight”, thus, the influence of someone’s opinion on weight gain directly affecting another person. Such a relationship can be directly applied to cascading effects that we learned in class. For example, person A’s friend B buys a tasty, not-so-healthy brand of ice cream. B tells A how great it is. A, dismayed by the lack of nutritional value of the ice cream, is hesitant to buy it. A’s friend C does not quite have A’s will-power, and buys some of the ice cream also. C also tells A how wonderful this ice cream is. Now A, with two positive signals about the ice cream, is likely to want to find out about this awesome ice cream, despite its health drawbacks. Cascading is now likely to happen: A’s other friends may hear about how A, B, and C all liked this ice cream, and are then compelled to find out the truth for themselves. So we see that the cascading effect indeed influenced these people to make a choice detrimental to their health.