Jonah Lehrer writes in Wired about two researchers using network theory and data mining to understand how obesity spread in the American population: "The Buddy System: How Medical Data Revealed Secret to Health and Happiness".
The two researchers thought the Framingham social network might demonstrate how relationships directly influence behavior and thus health and happiness. Since the study had tracked its subjects' weight for decades, Christakis and Fowler first analyzed obesity. Clicking through the years, they watched the condition spread to nearly 40 percent of the population. Fowler shows me an animation of their study—30 years of data reduced to 108 seconds of shifting circles and lines. Each circle represents an individual. Size is proportional to body mass index; yellow indicates obesity. "This woman is about to get big," Fowler says. "And look at this cluster. They all gain weight at about the same time."
Some neat visualizations accompany the story.